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For peer review only
Seasonal change in bone, muscle and fat in professional rugby league players and relationship to injury: a cohort
study
Journal: BMJ Open
Manuscript ID: bmjopen-2012-001400
Article Type: Research
Date Submitted by the Author: 07-Jun-2012
Complete List of Authors: Georgeson, Erin; Griffith University, Centre for Musculoskeletal Research Weeks, Benjamin; Griffith University, Centre for Musculoskeletal Research McLellan, Chris; Gold Coast Titans, National Rugby League
Beck, Belinda; Griffith University, Centre for Musculoskeletal Research
<b>Primary Subject Heading</b>:
Sports and exercise medicine
Secondary Subject Heading: Radiology and imaging
Keywords: Calcium & bone < DIABETES & ENDOCRINOLOGY, Bone diseases < ORTHOPAEDIC & TRAUMA SURGERY, Orthopaedic sports trauma < ORTHOPAEDIC & TRAUMA SURGERY
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Title: Seasonal change in bone, muscle and fat in professional rugby league players and
relationship to injury: a cohort study
Authors:
Erin C. Georgeson, BPhty(Hons) BExSc1
Benjamin K. Weeks, PhD1
Chris McLellan, PhD2
Belinda R. Beck, PhD1
1School of Physiotherapy and Exercise Science, Centre for Musculoskeletal Research,
Griffith Health Institute, Gold Coast, Australia; 2Gold Coast Titans, Gold Coast, Australia
Key Words: football, body composition, bone mass, sports injury
Corresponding author:
A/Prof Belinda R. Beck
School of Physiotherapy and Exercise Science
Gold Coast campus
Griffith University, Qld 4222
Australia
Ph: +61 7 5552 8793
Fax: +61 7 5552 8674
Email: [email protected]
Word Count: 2974
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Article Focus
• Does rugby league player body composition change across a 12 month period in
response to pre-season training, seasonal game play and off-season rest?
• Is pre-season body composition (bone, muscle and fat) related to injury incidence
throughout the season?
• Are changes in body composition during the playing season related to incidence of
injuries?
Key Messages
• Professional rugby league players lose lean mass across a playing season but regain it
with pre-season training
• Strong relationships were not detected between anthropometric characteristics and
incidence of injury.
Strengths and Limitations
• Very comprehensive anthropometric data was collected from a professional rugby
league team at four time points across a 12 month period (pre, mid, post and pre-
season) to track changes in body composition related to pre-season training, playing
and off seasons
• The most valid and reliable instruments (DXA and pQCT) were employed to
determine anthropometric measures. pQCT data is novel in this cohort.
• Low absolute number of injuries limited the ability to detect strong relationships
between injuries and anthropometric measures.
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ABSTRACT
Objectives To examine the anthropometric characteristics of an Australian National Rugby
League team and identify the relationship to type and incidence of injuries sustained during a
professional season. It was hypothesized that body composition would not change discernibly
across a playing season and that injury would be negatively related to pre-season bone and
muscle mass.
Design A repeated measure, prospective, observational, cohort study
Setting Griffith University and Titans Centre of Excellence, Gold Coast, Australia
Participants 37 professional male Australian National Rugby League players (mean age
24.3 ± 3.8) were recruited for pre-season 1 testing, of whom 25 were retested pre-season 2.
Primary and Secondary Outcome Measures Primary outcome measures included:
biometrics; body composition (bone, muscle and fat mass; dual-energy x-ray absorptiometry;
DXA; XR800, Norland Medical Systems, Inc); bone geometry and strength (peripheral
quantitative computed tomography; pQCT; XCT 3000, Stratec); calcaneal broadband
ultrasound attenuation (BUA; QUS-2, Quidel); diet and physical activity history. Secondary
outcome measures included player injuries across a single playing season.
Results Lean mass decreased progressively throughout the season (p ≤ 0.05), while whole
body (WB) bone mineral density (BMD) increased until mid-season (p ≤ 0.001) then
decreased thereafter (p ≤ 0.001). Start-of-season WB BMD, fat and lean mass, weight and
tibial mass measured at the 38% site predicted bone injury incidence, but no other
relationship was observed between body composition and injury.
Conclusions Significant anthropometric changes were observed in players across a
professional rugby league season; including an overall loss of muscle and an initial increase,
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followed by a decrease in bone mass. Strong relationships between anthropometry and
incidence of injury were not observed. Long term tracking of large rugby league cohorts is
indicated to obtain more injury data in order to examine anthropometric relationships with
greater statistical power.
There is no additional data available.
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INTRODUCTION
Rugby league is a physically demanding, high impact, full body contact professional sport,
requiring well developed muscle strength and endurance, speed, agility and aerobic power.[1]
The high frequency and force of physical collisions encountered during a game[2-4] leads to
a higher incidence of musculoskeletal injuries[5] than is typically observed in other team
sports.[2, 3, 6] Injury incidence has been reported from 44.9 to 462.7 injuries per 1000
player hours.[2, 7-9] As 15-30% of total seasonal injuries are classified “severe”[2, 8, 10]
players can miss up to 20% of games in a season.[7] A range of factors have been associated
with an increased risk of injury, including low preseason running speed and maximal aerobic
power, lighter body weight and greater number of playing years’ experience.[5]
Furthermore, injury risk is dependent on player position (e.g. forwards vs. backs); forwards
typically sustaining more injuries than backs.[9, 11]
Some anthropometric and physiological characteristics of rugby league players have been
described, based on traditional body composition measures of weight, height, body mass
index (BMI) and skinfold thickness. Few more direct measures of bone and muscle have
been reported, and the relationship of body composition to injury remains unknown.
Analysis of seasonal anthropometric changes to rugby league players and the examination of
relationships of anthropometrics with rate and type of injury may reveal important risk
factors. In particular, the identification of modifiable risk factors would give rise to
opportunities to reduce the risk of injury to players.
Dual-energy x-ray absorptiometry (DXA) provides a reliable estimate of body composition
(bone, muscle and fat).[12] A recent study of English Super League players observed an
increase in body fat from DXA across the playing season, and a decrease in lean mass.[13]
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Bone mass was also observed to increase to mid-season, but decrease thereafter. It is well
known that DXA estimates of bone mass are based on two dimensional measures of areal
bone mineral density that cannot fully account for bone size, discriminate between cortical
and trabecular bone envelopes, or measure elements of bone morphology that are critical to
whole bone strength. In light of the known limitations of DXA measures, seasonal changes
in rugby league player bone strength remains uncertain. Peripheral quantitative computed
tomography (pQCT) can discriminate between cortical and trabecular envelopes, and
measures true volumetric BMD and parameters of bone morphology; thereby providing a
superior indication of bone strength than DXA.[14-17] Such measures have not previously
been reported for a rugby league cohort.
The aim of the current study was to examine pre-, mid- and post season body composition of
a professional Australian team using DXA and pQCT, and to identify relationships between
baseline and change in body composition with rate and type of injuries sustained across a
season.
METHODS
Ethical approval
Ethical approval for the study was granted by the Griffith University Human Research Ethics
Committee (PES/28/08/HREC). Written informed consent was obtained from each
participant.
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Subjects
All members of the Gold Coast Titans National Rugby League team (n=44) (mean age 24.6 ±
3.4 years) consented to participate in the study.
Study design and conduct
A repeated measure, prospective, observational study was conducted. Data was collected on
four occasions over a 12-month period, that is, pre- (March), mid- (July) and post-2009
southern hemisphere rugby league season (September/October), and pre-2010 rugby league
season (March). All data was collected in the Bone Densitometry Research Laboratory at
Griffith University, Gold Coast.
Behavioral characteristics – Diet and physical activity
Nutrition was assessed via the Cancer Council Victoria’s Dietary Questionnaire for
Epidemiological Studies (DQES), a diet instrument validated for the Australian
population.[18] The DQES contains a series of questions pertaining to the subjects’ normal
dietary intake over the preceding 12 months. Responses were computer-analysed and an
estimate of total daily energy intake and calcium intake were obtained.
The Bone-specific Physical Activity Questionnaire (BPAQ) is a validated tool for quantifying
historical physical activity participation relevant to the musculoskeletal system.[19]
Participants were asked to record: 1) all regular physical activities performed throughout their
life and the approximate number of years of participation; and 2) all activities performed on a
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regular basis over the previous 12 months, including frequency of participation. The BPAQ
was analysed using a custom-designed program (available at
http://www.fithdysign.com/BPAQ/) developed on LabVIEW software (National Instruments,
Texas, USA) to produce current, past and total bone-specific physical activity history
scores.[19]
Biometrics
Subject height was measured to the nearest 0.01 m using a wall-mounted stadiometer (HART
Sport & Leisure, Brisbane, Australia). Weight was measured to the nearest 0.01 kg using a
robust digital scale (CH-150K, AND Mercury, Brisbane, Australia). Upper extremity skeletal
dominance was determined as the preferred writing hand. Lower extremity skeletal
dominance was determined to be the non-kicking leg according to procedures established and
validated in our laboratory.[20]
Anthropometry
Dual-energy X-ray Absorptiometry
Dual-energy x-ray absorptiometry (DXA) was used to determine whole body (WB), lumbar
spine (LS), non-dominant femoral neck (FN) and forearm (FA) bone mineral content (BMC;
g), bone area (cm2), and bone mineral density (BMD; g/cm
2) (XR800 Norland Cooper
Surgical, USA, Illuminatus software Version 4.2.4). Additionally, WB scans were used to
determine lean and fat mass. Short-term BMD measurement precision in our lab is 0.9%,
1.1%, 0.4%, 0.8% and 0.6% for WB, FN, LS, distal radius-ulna and proximal radius-ulna
respectively.
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Peripheral Quantitative Computed Tomography
Peripheral Quantitative Computed Tomography (pQCT; XCT 3000; Stratec Pforzheim,
Germany) was used to examine non-dominant tibiae total, trabecular and cortical tibial
volumetric densities (mg/cm3), strength-strain index (SSI; mm
3), principal moments of inertia
(Imin and Imax; mm4) and muscle area (mm
2) at the 4%, 38% and 66% sites. Short term
measurement precision in our lab is 1.5% and 0.6% for total tibial density at the 4% and 38%
sites respectively.
Quantitative Ultrasound
Quantitative Ultrasound (QUS-2; Quidel, Mountain View, Ca) was used to measure
broadband ultrasound attenuation (BUA; dB/MHz) of the non-dominant calcaneus. Short-
term measurement precision with repositioning was 2.5%.
Performance Measures
Single Leg Stance
Static balance ability was tested using the standard single leg stance (SLS) test.[21]
Participants stood with feet pelvis-width apart, forearms crossed over their chest, and fingers
at shoulders. With eyes closed, one foot was lifted off the ground to the level of the opposite
ankle, but not touching. Timing commenced from foot lift off and ceased when: 1) arms
moved from their starting position; 2) feet touched; 3) elevated foot touched the ground or
moved towards/away from the planted foot; 4) grounded foot adjusted position to maintain
balance; or 5) eyes opened. Each participant was allowed to practice and have up to three
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attempts on each leg. The subject’s best time was recorded in seconds and the test repeated
for the opposite leg. A single investigator performed all SLS tests.
Vertical Jump
Leg muscle power was assessed by the vertical jump test.[22] Participants began by standing
beside the Yardstick vertical jump device (Swift Performance Equipment, NSW, Australia),
with both feet grounded and positioned shoulder-width apart. The participant was asked to
reach as high as possible with their preferred arm and the height of reach was recorded.
Participants were then instructed to jump as high as possible in counter-movement fashion
without arm swing, and tap the device at the peak of their jump. The best of three attempts
was recorded in cm. A single investigator measured and recorded all vertical jump trials.
Injury Data Collection
All injuries, new or recurrent, sustained during the study period were recorded by two team
physiotherapists in attendance at all games and training sessions. An injury was recorded if a
rugby league activity/game resulted in any pain, discomfort, illness or disability, and required
the player to seek medical intervention from team medical staff.[23] All injuries were
recorded whether the player missed a subsequent training session/game or not. Injury details
including anatomical location and tissue involvement, cause and severity (determined by the
number of training days and games missed) were recorded.
Game exposure hours were calculated by multiplying the number of players, by the number
of games and the duration of the match (i.e. 13 players x 29 games x 1.33 hours/game).[23]
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Injury incidence was recorded per 1000 game or training hours.[2, 23, 24] Match injury
incidence was calculated by dividing the number of recorded match injuries by the game
exposure hours and multiplying by 1000.
Statistical Analysis
Statistical analysis was performed using SPSS version 17.0 for Windows (IBM, Chicago, IL,
USA). Descriptive statistics (mean ± SD) were generated for subject and injury
characteristics and independent T-tests of the original 2009 cohort (n=37) were used to
compare the anthropometric characteristics of injured versus non-injured players. Correlation
analyses were performed to identify relationships between injury incidence, biometrics,
anthropometrics, active test performance, and lifestyle factors of the 2009 cohort (n=37).
Subsequent multiple regression analyses were used to determine the ability of biometrics and
behavioural characteristics to predict variance in anthropometrics and injury incidence.
Levene’s test was used to examine homogeneity of variance. To examine change in
anthropometric characteristics across the season, one-way repeated measures ANOVA was
used, both with and without covariates of calcium, weight, age and past BPAQ score (n=37).
Results were considered statistically significant at p ≤ 0.05.
RESULTS
A total of 44 different subjects were tested. At baseline 2009, 37 players were tested and 32
were tested in 2010. Player relocation resulted in 12 players leaving the cohort at the end of
the 2009 season and seven players joining the study prior to 2010 testing. Table 1 describes
the baseline characteristics of the cohort. Notably players exhibited bone mass that was, on
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average, over one standard deviation higher than age- and sex-matched norms for the WB (Z-
score range = + 0.63 to +1.63), spine (Z-score range = + 0.99 to +2.39) and hip (Z-score
range = + 0.63 to +3.03).
Table 1 Baseline Characteristics of Players at 2009 Pre-Season (n = 37)
Age (years) 24.3 ± 3.8
Weight (kg) 95.3 ± 10.4
Height (m) 1.81 ± 0.06
BMI (kg/m2) 29.0 ± 2.3
BPAQ Past 72.4 ± 26.9
BPAQ Current 7.5 ± 1.0
BPAQ Total 40.0 ± 13.5
WB BMD (g/cm2) 1.251 ± 0.088
WB BMD Z-score 1.13 ± 0.50
Total Daily Energy (kJ) 11052 ± 3678
Daily Ca2+
(mg) 1224 ± 454 BMI: body mass index; BPAQ: bone-specific physical activity; Ca
2+: calcium;
WB BMD: whole body bone mineral density.
Anthropometric Measures
Bone, muscle and fat measures at all four testing sessions are presented in Table 2.
Controlling for age, weight, dietary energy intake, calcium consumption and past physical
activity, lean mass decreased at each measurement time point throughout the 2009 season,
but returned to pre-2009 season values by 2010 pre-season (p ≤ 0.05). Fat mass did not
change over the 12-month period (p ≥ 0.05). The lean and fat percent response followed a
similar pattern (Figures 1A and B).
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Table 2 DXA and pQCT parameters at all measurement time points
Stage of Season
Measure Pre 2009 Mid 2009 Post 2009 Pre 2010
WB BMD (g/cm2)
(n = 19)
1.235±0.087a,e,f 1.296±0.093b,c 1.256±0.100
1.245±0.087
LS BMD (g/cm
2)
(n = 20)
1.447±0.110
1.460±0.105
1.459±0.116
1.469±0.114
FN BMD (g/cm
2)
(n = 19)
1.319±0.130
1.333±0.132
1.335±0.133
1.324±0.134
Dist. R&U BMD (g/cm2)
(n = 18)
0.580±0.051a
0.573±0.050b
0.580±0.050
0.578±0.049
Prox. Rad BMD (g/cm
2)
(n = 18)
1.065±0.063e
1.071±0.062b
1.078±0.062d
1.068±0.056
WB Lean Mass (kg)
(n = 19)
81.45±7.76a, e
80.72±7.73
79.89±6.72
d
81.22±6.73
WB Fat Mass (kg)
(n = 19)
10.70±3.08
11.05±4.00
11.03±4.87
11.35±4.46
BMI (kg/m
2)
(n = 20)
28.65±1.90
28.62±2.03
28.49±2.08
28.67±1.94
BUA (dB/MHz)
(n = 20)
118.3±15.3
117.9±16.8
117.4±16.3
117.6±15.3
Tibial Mass at 4% site (g/cm)
(n = 20)
5.55±0.85 5.55±0.90
5.52±0.77 5.59±0.88
Tibial Mass at 38% site (g/cm)
(n = 19)
5.37±0.53a,e,f
5.41±0.53
5.42±0.57
5.41±0.50
Leg Bone:Muscle Area, 66%
Site(%) (n=20)
5.33±0.52a,f 5.51±0.56 5.49±0.61 5.50±0.62
Leg Fat Area, 66% site (mm2)
(n=20)
1005±590a
1303±549 1195±455 1135±592
BMD: bone mineral density; BMI: body mass index; BUA: broadband ultrasound attenuation; Dist. R&U BMD:
distal radius and ulna BMD; FN BMD: femoral neck BMD; LS BMD: lumbar spine BMD; NS: not significant;
Prox. Rad BMD: proximal radius BMD; WB: whole body; a: sig. difference between pre-2009 and mid-2009;
b: sig. difference between mid-2009 and post-2009; c: sig. difference between mid-2009 and pre-2010; d: sig.
difference between post-2009 and pre-2010; e: sig. difference between pre-2009 and post-2009; f: sig.
difference between pre-2009 and pre-2010.
Only WB BMD changed significantly across the 2009 season (p ≤ 0.001), increasing until
mid-season (p ≤ 0.001) and decreasing thereafter (post-season 2009 and pre-season 2010 p ≤
0.001), but remaining higher than 2009 pre-season values (Figure 2A). No significant
changes were observed for LS or FN BMD over the 12-month period (Figures 2B & C);
however changes were evident for forearm BMD. Distal forearm BMD decreased until mid-
season (p ≤ 0.05; Figure 2D), with a subsequent significant increase from mid- to post-season
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(p ≤ 0.05), at which time BMD of the proximal radius and ulna also significantly increased (p
≤ 0.05; Figure 2E). Proximal radius BMD decreased from 2009 post-season to 2010 pre-
season (p ≤ 0.05).
No significant changes were observed in tibial mass at the 4% tibial site (p = 0.364). Tibial
mass increased at the 14% site over the 12 month period (p ≤ 0.05) and at the 38% site at
each time-point relative to pre-season 2009 (p ≤ 0.05; Figure 2F).
Exposure and Injuries
A total of 29 games were played during the 2009 National Rugby League season, inclusive of
three pre-season and two finals matches for a total team game exposure of 501 hours (13
players x 29 games x 1.33 hours).[25] A total of 51 injuries were reported across the 2009
season, equating to an incidence of roughly 101 injuries per 1000 player hours. There were
43 new injuries and 8 re-injuries. Twelve injuries occurred when players were running, 21
while being tackled, 4 when tackling another player, 1 when kicking, 8 from a collision, 1
from a fall, and 4 were of unknown cause. The players’ dominant sides were affected 45% of
the time. Injury types are presented in Table 3. Injuries were classified into one of four
categories: bone (fracture or bone bruise), muscle (tear or strain), joint disruption (connective
tissue/ligament/tendon injury or dislocation) or impact injury (haematoma/contusion,
concussion or rib/sternal injury) and plotted in Figure 4.
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Table 3 Injuries sustained throughout the 2009 season (n = 37)
Type of Injury
Upper Limb
Glenohumeral Joint dislocation
Glenoid Labral lesion
Rotator Cuff impingement
Acromioclavicular Joint sprain
Scapho-lunate Ligament sprain
Carpometocarpal Joint sprain
Metacarpal fracture
Lower Limb
Calcaneal Fat Pad bruise
Lateral Ankle sprain
Gastrocnemius contusion
Hamstring strain
Achilles Tendinopathy
Adductor muscle tear
Gastrocnemius tear
Femoral Condyle bruise
Patella bruise
Quadriceps strain
Patella tendinosis
Fibula bruise
Anterior Cruciate Ligament tear
Head and Torso
Rib Cartilage sprain
Concussion
Sternal bruise
Back contusion
Intercostal muscle strain
3
3
3
3
3
3
1
4
3
4
2
3
2
2
1
1
2
3
1
3
4
4
4
4
2
1: Bone-related injury; 2: Muscle-related injury; 3: Joint-related injury;
4: Impact-related injury
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There were no differences in baseline BMI, BUA, WB BMD and BMC, WB lean and fat
mass, and tibial mass at the 38% site (p > 0.05) between injured (n=20) and non-injured
(n=16) players. No factor predicted injury incidence or muscle, connective tissue or impact
injuries. By contrast, baseline WB BMD, fat mass, lean mass, weight and tibial mass at the
38% site accounted for around 53% of the variance in bone-related injuries (R2 = 0.527; p =
0.003).
DISCUSSION
Our objective was to examine the anthropometric characteristics of Australian National
Rugby League players, pre-, mid- and post season, to determine if relationships exist between
those characteristics, and the incidence and type of injuries sustained during a professional
season. We found body composition changed throughout the season, with players tending to
lose lean mass and gain fat mass as the season progressed. We also observed WB BMD
increased until mid-season and decreased thereafter. Body composition elements were
largely unrelated to injury incidence and type throughout the season. Only start-of-season
WB BMD, fat and lean mass, weight and tibial mass (38% site) contributed to the prediction
of bone injury incidence.
Soft tissue changes
Our observation that players lost lean mass across the season paralleled those of a recent
report of body composition changes of English Super League players, however we did not
observe the increase in body fat of that study,[13] or of a skinfold study of adult amateur
Australian Rugby League players.[26]
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We suggest that the lean mass changes reflect the reduction in players’ strength and
resistance training regime from 2-4 sessions per week in the pre-season, to only 1-2 sessions
per week during the season, when a greater emphasis was placed on match preparation and
physical recovery. Markedly increased playing exposure and intensity, including
representative games, had the effect of reducing between-game recovery time such that
fatigue, microtrauma and injuries[5, 11, 13] reduce the capacity for fitness and strength
training. The implications of the observed lean tissue changes are unclear. It is possible that
reductions in lean mass may reduce muscle strength and endurance, speed, agility and power
across the course of the season;[1] however the degree of such an effect would be difficult to
quantify.
Bone changes
It was not unexpected to find that the average bone mass of the elite rugby league players at
each DXA measured site was considerably higher than the “normal” population. The
majority of players participating in the current study began playing football prior to, or during
their adolescent years, a time when bone is highly responsive to mechanical loading.[27]
While it is difficult to differentiate the influence of self-selection (more physically robust
individuals tolerating the rigours of rugby league playing at the elite level better than more
diminutive individuals) from the osteogenic effect of rugby league playing, the observed
seasonal variation in bone mass is informative. The WB BMD gain to mid-season, is likely
attributable to the highly favourable pre-season loading stimulus of high intensity fitness and
resistance training, coupled with a typically tardy bone remodelling response. The
subsequent loss in the latter stages of the season may reflect a relative “detraining” effect on
an “over-adapted” skeleton as training time and intensity is dramatically reduced to optimise
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game and injury recovery. An increase in WB BMD from preseason 2009 to preseason 2010
is indicative of continued maturational growth in the relatively young cohort. This
observation is especially meaningful in light of the observed bone changes across a playing
season suggesting that even the robust skeletons of very highly trained young adult male
athletes are sensitive to subtle changes in mechanical loading.
The current study is the first to examine the baseline and seasonal changes in elite rugby
league player bone morphology and volumetric density from pQCT. While the significant
increase in proximal tibial mass (38% site) across the season has not previously been
observed, we found no relationship between any pQCT parameter and player injury. The
lack of observed relationship is potentially related to the small sample size and relatively
small number of injuries. Further pQCT data collection is indicated.
Our results revealed that the average BMI of all players, irrespective of position, was higher
than the recommended BMI guidelines (18.5-25 kg/m2),[28] thereby classifying the cohort as
overweight or obese. In this case the metric clearly misrepresents the endomorphic
mesomorph physiques of rugby league players.[28] Indeed, our DXA findings indicate that
rugby league player body composition is largely comprised of lean mass (average 80.6 kg =
84.9 %) with only a small proportion of fat (average 12.2 kg = 8.7 %). Our findings confirm
that BMI should not be used to track changes in body composition in mesomorphic
athletes.[13]
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Injuries
Joint disruption injuries were the most common injury sustained (Figure 4) which is in partial
agreement with previous reports,[2, 5, 29] but not all [9-11, 30]. Start-of-season
anthropometric factors had limited ability to predict injury incidence or type throughout the
season. Furthermore, there were no correlations between any anthropometric factors and
muscle, connective tissue or impact injuries; however, WB BMD, fat and lean mass, weight
and tibial mass at the 38% site were predictive of bone-related injuries.
Limitations
While the total participant numbers in our study are comparable to that of other reports,[13,
31] reduced player attendance at 2009 post-season testing somewhat weakened statistical
power. The relatively low injury numbers also limited our ability to detect significant
associations with risk factors.
Conclusion
We observed an overall loss in lean mass of players throughout a professional rugby league
season. This was accompanied by an increase in WB BMD until mid-season, which
progressively decreased thereafter. We did not identify any strong relationships between body
composition and injuries, with the exception of a relationship between baseline WB BMD, fat
and lean mass, weight and tibial mass (38% site) and bone injury incidence. Longer term
tracking of rugby league player body composition and injuries is warranted.
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What this study adds
• Rugby league player muscle mass decreases across a professional season, and WB BMD
increases until mid-season, decreasing thereafter.
• Start of season WB BMD, fat and lean mass, weight and tibial mass (38% site) may be
associated with incidence of rugby league player bone injury.
Acknowledgements The authors would like to thank the Gold Coast Titans staff and players
who participated in the study.
Funding None
Competing Interests None
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REFERENCES
1. Meir R. Evaluating players fitness in professional rugby league : reducing
subjectivity. Strength Cond Coach 1993;1:11-7.
2. Gibbs N. Injuries in professional rugby league: a three-year prospective study of the
South Sydney Professional Rugby League Football Club. Am J Sports Med 1993;21:696-700.
3. Seward H, Orchard J, Hazard H, et al. Football injuries in Australia at the elite level.
Med J Aust 1993;159:298-301.
4. Gabbett TJ, Domrow N. Relationships between training load, injury, and fitness in
sub-elite collision sport athletes. J Sports Sci 2007;25:1507-19.
5. Gabbett TJ, Domrow N. Risk factors for injury in subelite rugby league players. Am J
Sports Med 2005;33:428-34.
6. Gabbett T, Kelly J, Ralph S, et al. Physiological and anthropometric characteristics of
junior elite and sub-elite rugby league players, with special reference to starters and non-
starters. J Sci Med Sport 2009;12:215-22.
7. Gissane C, Jennings D, Kerr K, et al. A pooled data analysis of injury incidence in
rugby league football. Sports Med 2002;32:211-6.
8. Phillips LH, Standen PJ, Batt ME. Effects of seasonal change in rugby league on the
incidence of injury. Br J Sports Med 1998;32:144-8.
9. Stephenson S, Gissane C, Jennings D. Injury in rugby league: a four year prospective
survey. Br J Sports Med 1996;30:331-4.
10. Gabbett TJ. Severity and cost of injuries in amateur rugby league: a case study. J
Sports Sci 2001;19:341-7.
11. Gabbett TJ. Incidence, site, and nature of injuries in amateur rugby league over three
consecutive seasons. Br J Sports Med 2000;34:98-103.
Page 21 of 29
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jopen.bmj.com
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MJ O
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ovember 2012. D
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For peer review only
22
12. Van der Ploeg GE, Withers RT, Laforgia J. Percent body fat via DEXA: comparison
with a four-compartment model. J App Phys 2003;94:499-506.
13. Harley JA, Hind K, O'Hara JP. Three-compartment body composition changes in elite
rugby league players during a super league season, measured by dual-energy X-ray
absorptiometry. J Strength Cond Res 2011;25:1024-9.
14. Haapasalo H, Kontulainen S, Sievänen H, et al. Exercise-induced bone gain is due to
enlargement in bone size without a change in volumetric bone density: a peripheral
quantitative computed tomography study of the upper arms of male tennis players. Bone
2000;27:351-7.
15. Sawada K, Morishige K, Ohmichi M, et al. Peripheral quantitative computed
tomography (pQCT) is useful for monitoring bone mineral density of the patients who
receive hormone replacement therapy. Maturitas 2007;56:343-9.
16. Schoenau E, Neu CM, Rauch F, et al. The development of bone strength at the
proximal radius during childhood and adolescence. J Clin Endocrinol Metab 2001;86:613-8.
17. Tsurusaki K, Ito M, Hayashi K. Differential effects of menopause and metabolic
disease on trabecular and cortical bone assessed by peripheral quantitative computed
tomography (pQCT). Br J Radiol 2000;73:14-22.
18. Giles GC, Ireland PD. Dietary Questionnaire for Epidemiological Studies (Version 2).
Melbourne: The Cancer Council Victoria; 1996.
19. Weeks BK, Beck BR. The BPAQ: a bone-specific physical activity assessment
instrument. Osteoporos Int 2008;19:1567-77.
20. Beck BR, Weeks BK. Which limb to scan? Revisiting the relationship between
functional and skeletal limb dominance. J Bone Miner Res 2010;25.
21. Guskiewicz KM, Perrin DH. Research and clinical applications of assessing balance. J
Sport Rehab 1996;5:45-63.
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
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ovember 2012. D
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23
22. Cochrane DJ, Stannard SR. Acute whole body vibration training increases vertical
jump and flexibility performance in elite female field hockey players. Br J Sports Med
2005;39:860-5.
23. King DA, Gabbett TJ, Gissane C, et al. Epidemiological studies of injuries in rugby
league: suggestions for definitions, data collection and reporting methods. J Sci Med Sport
2009;12:12-9.
24. Gabbett TJ. Incidence of injury in amateur rugby league sevens. Br J Sports Med
2002;36:23-6.
25. King T, Jenkins D, Gabbett T. A time-motion analysis of professional rugby league
match-play. J Sports Sci 2009;27:213-9.
26. Gabbett TJ. Changes in physiological and anthropometric characteristics of rugby
league players during a competitive season. J Strength Cond Res 2005;19:400-8.
27. Ginty F, Rennie KL, Mills L, et al. Positive, site-specific associations between bone
mineral status, fitness, and time spent at high-impact activities in 16- to 18-year-old boys.
Bone 2005;36:101-10.
28. Lundy B, O'Connor H, Pelly F, et al. Anthropometric characteristics and competition
dietary intakes of professional rugby league players. Int J Sport Nutr Exerc Metab
2006;16:199-213.
29. Gabbett TJ. Influence of the limited interchange rule on injury rates in sub-elite rugby
league players. J Sci Med Sport 2005;8:111-5.
30. Gabbett. Incidence of injury in semi-professional rugby league players. Br J Sports
Med 2003;37:36-43.
31. Elloumi M, Ben Ounis O, Courteix D, et al. Long-term rugby practice enhances bone
mass and metabolism in relation with physical fitness and playing position. J Bone Miner
Metab 2009;27:713-20.
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FIGURE LEGENDS
Figure 1 Change in percent lean (A) and percent fat (B) of players measured at all testing
time points (n=19). ( * Significantly different from baseline; ∆ Significant change between time points).
Figure 2 Seasonal change in whole body (A; n=19), lumbar spine (B; n=20), femoral neck
(C; n=19), distal radius (D; n=18) and proximal radius (E; n=18) bone mineral density
(BMD) and tibial bone mass (F) at 4% (n=20) and 38% (n=19) sites of professional rugby
league players. (* Significantly different from baseline; ∆ Significant change between time points).
Figure 3 Frequency distribution by injury category of professional rugby league players
across a playing season (n=37)
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201x74mm (300 x 300 DPI)
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206x217mm (300 x 300 DPI)
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153x127mm (300 x 300 DPI)
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STROBE 2007 (v4) Statement—Checklist of items that should be included in reports of cohort studies
Section/Topic Item
# Recommendation Reported on page #
Title and abstract 1 (a) Indicate the study’s design with a commonly used term in the title or the abstract 1
(b) Provide in the abstract an informative and balanced summary of what was done and what was found 3
Introduction
Background/rationale 2 Explain the scientific background and rationale for the investigation being reported 5
Objectives 3 State specific objectives, including any prespecified hypotheses 6
Methods
Study design 4 Present key elements of study design early in the paper 7
Setting 5 Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow-up, and data
collection
7
Participants 6 (a) Give the eligibility criteria, and the sources and methods of selection of participants. Describe methods of follow-up 7
(b) For matched studies, give matching criteria and number of exposed and unexposed N/A
Variables 7 Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers. Give diagnostic criteria, if
applicable
7-10
Data sources/
measurement
8* For each variable of interest, give sources of data and details of methods of assessment (measurement). Describe
comparability of assessment methods if there is more than one group
7-11
Bias 9 Describe any efforts to address potential sources of bias N/A
Study size 10 Explain how the study size was arrived at 7
Quantitative variables 11 Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen and
why
11
Statistical methods 12 (a) Describe all statistical methods, including those used to control for confounding 11
(b) Describe any methods used to examine subgroups and interactions 11
(c) Explain how missing data were addressed N/A
(d) If applicable, explain how loss to follow-up was addressed N/A
(e) Describe any sensitivity analyses N/A
Results
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Participants 13* (a) Report numbers of individuals at each stage of study—eg numbers potentially eligible, examined for eligibility, confirmed
eligible, included in the study, completing follow-up, and analysed
11,12,13 (Table 2)
(b) Give reasons for non-participation at each stage 11
(c) Consider use of a flow diagram N/A
Descriptive data 14* (a) Give characteristics of study participants (eg demographic, clinical, social) and information on exposures and potential
confounders
11-12
(b) Indicate number of participants with missing data for each variable of interest Table 2 page 12
(c) Summarise follow-up time (eg, average and total amount) 7
Outcome data 15* Report numbers of outcome events or summary measures over time 11-16
Main results 16 (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision (eg, 95% confidence
interval). Make clear which confounders were adjusted for and why they were included
12-16
(b) Report category boundaries when continuous variables were categorized N/A
(c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time period N/A
Other analyses 17 Report other analyses done—eg analyses of subgroups and interactions, and sensitivity analyses N/A
Discussion
Key results 18 Summarise key results with reference to study objectives 16
Limitations
Interpretation 20 Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from
similar studies, and other relevant evidence
19
Generalisability 21 Discuss the generalisability (external validity) of the study results 19
Other information
Funding 22 Give the source of funding and the role of the funders for the present study and, if applicable, for the original study on
which the present article is based
20
*Give information separately for cases and controls in case-control studies and, if applicable, for exposed and unexposed groups in cohort and cross-sectional studies.
Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published examples of transparent reporting. The STROBE
checklist is best used in conjunction with this article (freely available on the Web sites of PLoS Medicine at http://www.plosmedicine.org/, Annals of Internal Medicine at
http://www.annals.org/, and Epidemiology at http://www.epidem.com/). Information on the STROBE Initiative is available at www.strobe-statement.org.
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Seasonal change in bone, muscle and fat in professional rugby league players and relationship to injury: a cohort
study
Journal: BMJ Open
Manuscript ID: bmjopen-2012-001400.R1
Article Type: Research
Date Submitted by the Author: 24-Jul-2012
Complete List of Authors: Georgeson, Erin; Griffith University, Centre for Musculoskeletal Research Weeks, Benjamin; Griffith University, Centre for Musculoskeletal Research McLellan, Chris; Bond University, Faculty of Health Sciences and Medicine
Beck, Belinda; Griffith University, Centre for Musculoskeletal Research
<b>Primary Subject Heading</b>:
Sports and exercise medicine
Secondary Subject Heading: Radiology and imaging
Keywords: Orthopaedic sports trauma < ORTHOPAEDIC & TRAUMA SURGERY, Musculoskeletal disorders < ORTHOPAEDIC & TRAUMA SURGERY, SPORTS MEDICINE
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1
1
Title: Seasonal change in bone, muscle and fat in professional rugby league players and 2
relationship to injury: a cohort study 3
4
Authors: 5
Erin C. Georgeson, BPhty(Hons) BExSc1 6
Benjamin K. Weeks, PhD1
7
Chris McLellan, PhD2
8
Belinda R. Beck, PhD1 9
1School of Physiotherapy and Exercise Science, Centre for Musculoskeletal Research, 10
Griffith Health Institute, Gold Coast, Australia; 2Faculty of Health Sciences and Medicine, 11
Bond University, Gold Coast, Australia 12
13
Key Words: football, body composition, bone mass, sports injury 14
15
Corresponding author: 16
A/Prof Belinda R. Beck 17
School of Physiotherapy and Exercise Science 18
Gold Coast campus 19
Griffith University, Qld 4222 20
Australia 21
Ph: +61 7 5552 8793 22
Fax: +61 7 5552 8674 23
Email: [email protected] 24
25
Word Count: 26
3798 - Intro to Conclusion including tables 27
3251 - Intro to Conclusion excluding tables 28
29
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Article Focus 1
• Does rugby league player body composition change across a 12 month period in 2
response to pre-season training, seasonal game play and off-season rest? 3
• Is pre-season body composition (bone, muscle and fat) related to injury incidence 4
throughout the season? 5
• Are changes in body composition during the playing season related to incidence of 6
injuries? 7
Key Messages 8
• Professional rugby league players lose lean mass across a playing season but regain it 9
with pre-season training 10
• Strong relationships were not detected between anthropometric characteristics and 11
incidence of injury. 12
Strengths and Limitations 13
• Comprehensive anthropometric data was collected from a professional rugby league 14
team at four time points across a 12 month period (pre, mid, post and pre-season) to 15
track changes in body composition related to pre-season training, playing and off 16
seasons. 17
• The most valid and reliable instruments (DXA and pQCT) were employed to 18
determine anthropometric measures. pQCT data is novel in this cohort. 19
• Low absolute number of injuries limited the ability to detect strong relationships 20
between injuries and anthropometric measures. 21
22
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ABSTRACT 1
Objectives To examine the anthropometric characteristics of an Australian National Rugby 2
League team and identify the relationship to type and incidence of injuries sustained during a 3
professional season. It was hypothesized that body composition would not change discernibly 4
across a season and that injury would be negatively related to pre-season bone and muscle 5
mass. 6
Design A repeated measure, prospective, observational, cohort study 7
Setting Griffith University, Gold Coast, Australia 8
Participants 37 professional male Australian National Rugby League players, 24.3(3.8) 9
years of age were recruited for pre-season 1 testing, of whom 25 were retested pre-season 2. 10
Primary and Secondary Outcome Measures Primary outcome measures included: 11
biometrics; body composition (bone, muscle and fat mass; DXA; XR800, Norland Medical 12
Systems, Inc); bone geometry and strength (pQCT; XCT 3000, Stratec); calcaneal broadband 13
ultrasound attenuation (BUA; QUS-2, Quidel); diet and physical activity history. Secondary 14
outcome measures included player injuries across a single playing season. 15
Results Lean mass decreased progressively throughout the season (pre = 81.45(7.76) kg; 16
post = 79.89(6.72) kg; P ≤ 0.05), while whole body (WB) bone mineral density (BMD) 17
increased until mid-season (pre = 1.235(0.087)g/cm2; mid =1.296(0.093) g/cm
2; P ≤ 0.001) 18
then decreased thereafter (post = 1.256(0.100); P ≤ 0.001). Start-of-season WB BMD, fat 19
and lean mass, weight and tibial mass measured at the 38% site predicted bone injury 20
incidence, but no other relationship was observed between body composition and injury. 21
Conclusions Significant anthropometric changes were observed in players across a 22
professional rugby league season; including an overall loss of muscle and an initial increase, 23
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followed by a decrease in bone mass. Strong relationships between anthropometry and 1
incidence of injury were not observed. Long term tracking of large rugby league cohorts is 2
indicated to obtain more injury data in order to examine anthropometric relationships with 3
greater statistical power. 4
5
Data Sharing: There is no additional data available. 6
Contributorship: EG: primary researcher; contributed to study design, data collection and 7
analysis; prepared the manuscript draft; assisted with editing and approved the final text. 8
BW: researcher; contributed to data collection and analysis; reviewed the manuscript draft; 9
edited and approved the final text. CM: Liaison with the Australian National Rugby League 10
club; assisted in recruiting and scheduling player testing times; contributed to data collection. 11
BB: researcher; responsible for initial study concept, design and liaising with the football 12
club; contributed to data collection and analysis; contributed to manuscript structure and 13
drafting; edited and approved the final text. 14
Funding: This research received no specific funding. 15
Competing Interests: There are no competing interests. 16
17
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INTRODUCTION 1
Rugby league is a physically demanding, high impact, full body contact professional sport It 2
requires well developed muscle strength and endurance, speed, agility and aerobic power.[1] 3
The high frequency and force of physical collisions encountered during a game[2-4] leads to 4
a higher incidence of musculoskeletal injuries[5] than is typically observed in other team 5
sports.[2, 3, 6] Injury incidence has been reported from 44.9 to 462.7 injuries per 1000 6
player hours.[2, 7-9] Such large variations in reported injury incidence may be attributed to 7
inter-study differences in definitions, data collection and reporting methods used.[10] 8
Furthermore, skill level, playing intensity and seasonal conditions have been suggested to 9
influence injury incidence.[2, 8, 9] As 15-30% of total seasonal injuries are classified 10
“severe” (i.e. causing a player to miss five or more games)[2, 8, 11] players can miss up to 11
20% of games in a season.[7] A range of factors have been associated with an increased risk 12
of injury, including low preseason running speed and maximal aerobic power, lighter body 13
weight and greater number of playing years’ experience.[5] Furthermore, injury risk is 14
dependent on player position (e.g. forwards vs. backs); forwards typically sustaining more 15
injuries than backs.[9, 12] 16
17
Some anthropometric and physiological characteristics of rugby league players have been 18
described, based on traditional body composition measures of weight, height, body mass 19
index (BMI) and skinfold thickness.[13, 14] Few more direct measures of bone and muscle 20
have been reported, and the relationship of body composition to injury remains unknown.[15] 21
Analysis of seasonal anthropometric changes to rugby league players and the examination of 22
relationships of anthropometrics with rate and type of injury may reveal important risk 23
factors. In particular, the identification of modifiable risk factors would give rise to 24
opportunities to reduce the risk of injury to players. 25
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1
Dual-energy x-ray absorptiometry (DXA) provides a reliable estimate of body composition 2
(bone, muscle and fat).[16] A recent study of English Super League players observed an 3
increase in body fat from DXA across the playing season, and a decrease in lean mass.[15] 4
Bone mass was also observed to increase to mid-season, but decrease thereafter. It is well 5
known that DXA estimates of bone mass are based on two dimensional measures of areal 6
bone mineral density that cannot fully account for bone size, discriminate between cortical 7
and trabecular bone envelopes, or measure elements of bone morphology that are critical to 8
whole bone strength. In light of the known limitations of DXA measures, seasonal changes 9
in rugby league player bone strength remains uncertain. Peripheral quantitative computed 10
tomography (pQCT) can discriminate between cortical and trabecular envelopes, and 11
measures true volumetric BMD and parameters of bone morphology; thereby providing a 12
superior indication of bone strength than DXA.[17-20] Such measures have not previously 13
been reported for a rugby league cohort. 14
15
The aim of the current study was to examine pre-, mid- and post season body composition of 16
a professional Australian team using DXA and pQCT, and to identify relationships between 17
baseline and change in body composition with rate and type of injuries sustained across a 18
season. 19
20
METHODS 21
Ethical approval 22
Ethical approval for the study was granted by the Griffith University Human Research Ethics 23
Committee (PES/28/08/HREC). Written informed consent was obtained from each 24
participant. 25
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Subjects 1
All members of an Australian National Rugby League team (n=44),age 24.6(3.4) years, 2
playing an average of 15.7(7.2) games (58% of the season) consented to participate in the 3
study. 4
5
Study design and conduct 6
A repeated measure, prospective, observational study was conducted. Data was collected on 7
four occasions over a 12-month period, that is, pre- (March), mid- (July) and post-2009 8
southern hemisphere rugby league season (September/October), and pre-2010 rugby league 9
season (March). All data was collected in the Bone Densitometry Research Laboratory at 10
Griffith University, Gold Coast. 11
12
Behavioral characteristics – Diet and physical activity 13
Nutrition was assessed via the Cancer Council Victoria’s Dietary Questionnaire for 14
Epidemiological Studies (DQES), a diet instrument validated for the Australian 15
population.[21] The DQES contains a series of questions pertaining to the subjects’ normal 16
dietary intake over the preceding 12 months. Responses were computer-analysed and an 17
estimate of total daily energy intake and calcium intake were obtained. 18
19
The Bone-specific Physical Activity Questionnaire (BPAQ) is a validated tool for quantifying 20
historical physical activity participation relevant to the musculoskeletal system.[22] 21
Participants were asked to record: 1) all regular physical activities performed throughout their 22
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life and the approximate number of years of participation; and 2) all activities performed on a 1
regular basis over the previous 12 months, including frequency of participation. The BPAQ 2
was analysed using a custom-designed program (available at 3
http://www.fithdysign.com/BPAQ/) developed on LabVIEW software (National Instruments, 4
Texas, USA) to produce current, past and total bone-specific physical activity history 5
scores.[22] All participants (n=44) completed diet and BPAQ questionnaires. 6
7
Biometrics 8
Subject height was measured to the nearest 0.01 m using a wall-mounted stadiometer (HART 9
Sport & Leisure, Brisbane, Australia). Weight was measured to the nearest 0.01 kg using a 10
robust digital scale (CH-150K, AND Mercury, Brisbane, Australia). Upper extremity skeletal 11
dominance was determined as the preferred writing hand. Lower extremity skeletal 12
dominance was determined to be the non-kicking leg according to procedures established and 13
validated in our laboratory.[23] 14
15
Anthropometry 16
Dual-energy X-ray Absorptiometry 17
Dual-energy x-ray absorptiometry (DXA) was used to determine whole body (WB), lumbar 18
spine (LS), non-dominant femoral neck (FN) and forearm (FA) bone mineral content (BMC; 19
g), bone area (cm2), and bone mineral density (BMD; g/cm
2) (XR800 Norland Cooper 20
Surgical, USA, Illuminatus software Version 4.2.4). Additionally, WB scans were used to 21
determine lean and fat mass. Short-term DXA measurement precision in our lab is 0.9%, 22
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1.1%, 0.4%, 0.8%, 0.6%, 0.8% and 2.3% for WB, FN, LS, distal radius-ulna, proximal 1
radius-ulna, lean and fat mass, respectively. 2
3
Peripheral Quantitative Computed Tomography 4
Peripheral Quantitative Computed Tomography (pQCT; XCT 3000; Stratec Pforzheim, 5
Germany) was used to examine non-dominant tibiae total, trabecular and cortical tibial 6
volumetric densities (mg/cm3), strength-strain index (SSI; mm
3), principal moments of inertia 7
(Imin and Imax; mm4) and muscle area (mm
2) at the 4%, 38% and 66% sites. Short term 8
measurement precision in our lab is 1.5% and 0.6% for total tibial density at the 4% and 38% 9
sites respectively. 10
11
Quantitative Ultrasound 12
Quantitative Ultrasound (QUS-2; Quidel, Mountain View, Ca) was used to measure 13
broadband ultrasound attenuation (BUA; dB/MHz) of the non-dominant calcaneus. Short-14
term measurement precision with repositioning was 2.5%. 15
16
Performance Measures 17
Single Leg Stance 18
Static balance ability was tested using the standard single leg stance (SLS) test.[24] 19
Participants stood with feet pelvis-width apart, forearms crossed over their chest, and fingers 20
at shoulders. With eyes closed, one foot was lifted off the ground to the level of the opposite 21
ankle, but not touching. Timing commenced from foot lift off and ceased when: 1) arms 22
moved from their starting position; 2) feet touched; 3) elevated foot touched the ground or 23
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moved towards/away from the planted foot; 4) grounded foot adjusted position to maintain 1
balance; or 5) eyes opened. Each participant was allowed to practice and have up to three 2
attempts on each leg. The subject’s best time was recorded in seconds and the test repeated 3
for the opposite leg. A single investigator performed all SLS tests. 4
5
Vertical Jump 6
Leg muscle power was assessed by the vertical jump test.[25] Participants began by standing 7
beside the Yardstick vertical jump device (Swift Performance Equipment, NSW, Australia), 8
with both feet grounded and positioned shoulder-width apart. The participant was asked to 9
reach as high as possible with their preferred arm and the height of reach was recorded. 10
Participants were then instructed to jump as high as possible in counter-movement fashion 11
without arm swing, and tap the device at the peak of their jump. The best of three attempts 12
was recorded in cm. A single investigator measured and recorded all vertical jump trials. 13
14
Injury Data Collection 15
All injuries, new or recurrent, sustained during the study period were recorded by two team 16
physiotherapists in attendance at all games and training sessions. An injury was recorded if a 17
rugby league activity/game resulted in any pain, discomfort, illness or disability, and required 18
the player to seek medical intervention from team medical staff.[10] All injuries were 19
recorded whether the player missed a subsequent training session/game or not. Injury details 20
including anatomical location and tissue involvement, cause and severity (determined by the 21
number of training days and games missed) were recorded. 22
23
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Game exposure hours were calculated by multiplying the number of players, by the number 1
of games and the duration of the match (i.e. 13 players x 29 games x 1.33 hours/game).[10] 2
Injury incidence was recorded per 1000 game or training hours.[2, 10, 26] Match injury 3
incidence was calculated by dividing the number of recorded match injuries by the game 4
exposure hours and multiplying by 1000. 5
6
Statistical Analysis 7
Statistical analysis was performed using SPSS version 17.0 for Windows (IBM, Chicago, IL, 8
USA). Descriptive statistics, mean(sd) were generated for subject and injury characteristics 9
and independent T-tests of the original 2009 cohort (n=37) were used to compare the 10
anthropometric characteristics of injured versus non-injured players. Correlation analyses 11
were performed to identify relationships between injury incidence, biometrics, 12
anthropometrics, active test performance, and lifestyle factors of the 2009 cohort (n=37). 13
Subsequent multiple regression analyses were used to determine the ability of biometrics and 14
behavioural characteristics to predict variance in anthropometrics and injury incidence. Q-Q 15
plots were generated to determine if data were normally distributed and Levene’s test was 16
used to examine homogeneity of variance. To examine change in anthropometric 17
characteristics across the season, repeated measures ANOVA was used, both with and 18
without covariates of calcium, weight, age and past BPAQ score (n=37). Results were 19
considered statistically significant at P ≤ 0.05. 20
21
RESULTS 22
A total of 44 different subjects were tested. At baseline 2009, 37 players were tested and 32 23
were tested in 2010. Player relocation resulted in 12 players leaving the cohort at the end of 24
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the 2009 season and seven players joining the study prior to 2010 testing. Table 1 describes 1
the baseline characteristics of the cohort. All data were normally distributed. Notably 2
players exhibited bone mass that was, on average, over one standard deviation higher than 3
age- and sex-matched norms for the WB (Z-score range = +0.63 to +1.63), spine (Z-score 4
range = +0.99 to +2.39) and femoral neck (Z-score range = +0.63 to +3.03). 5
Table 1 Baseline Characteristics of Players at 2009 Pre-Season (n = 37) 6
Age (years) 24.3(3.8)
Weight (kg) 95.3(10.4)
Height (m) 1.81(0.06)
BMI (kg/m2) 29.0(2.3)
BPAQ Past 72.4(26.9)
BPAQ Current 7.5(1.0)
BPAQ Total 40.0(13.5)
Age began playing rugby league (years) 8.0(3.8)
WB BMD (g/cm2) 1.251(0.088)
WB BMD Z-score 1.13(0.50)
Total Daily Energy (kJ) 11052(3678)
Daily Ca2+
(mg) 1224(454) BMI: body mass index; BPAQ: bone-specific physical activity; Ca
2+: calcium; 7
WB BMD: whole body bone mineral density. 8
9
Anthropometric and Performance Measures 10
Bone, muscle and fat measures at all four testing sessions are presented in Table 2. 11
Controlling for age, weight, dietary energy intake, calcium consumption and past physical 12
activity, lean mass decreased at each measurement time point throughout the 2009 season, 13
but returned to pre-2009 season values by 2010 pre-season (mean difference = 0.230, 95%CI 14
= -0.987-1.168-kg; P = 0.86). Neither weight (mean difference = 0.300, 95%CI =
-0.624-15
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1.225 kg, P = 0.51), nor fat mass (mean difference = 0.650, 95%CI = -0.441-1.656 kg, P = 1
0.24) changed over the 12-month period. The lean and fat percent response followed a 2
similar pattern (Figures 1A and B). 3
4
Table 2 DXA and pQCT parameters at all measurement time points 5
Stage of Season
Measure Pre 2009 Mid 2009 Post 2009 Pre 2010
WB BMD (g/cm2)
(n = 19)
1.235(0.087)a,e,f 1.296(0.093)
b,c 1.256(0.100)
1.245(0.087)
LS BMD (g/cm2)
(n = 20)
1.447(0.110)
1.460(0.105)
1.459(0.116)
1.469(0.114)
FN BMD (g/cm
2)
(n = 19)
1.319(0.130)
1.333(0.132)
1.335(0.133)
1.324(0.134)
Dist. R&U BMD (g/cm
2)
(n = 18)
0.580(0.051)a
0.573(0.050)
b
0.580(0.050)
0.578(0.049)
Prox. Rad BMD (g/cm2)
(n = 18)
1.065(0.063)e
1.071(0.062)b
1.078(0.062)d
1.068(0.056)
WB Lean Mass (kg)
(n = 19)
81.45(7.76)a, e
80.72(7.73)
79.89(6.72)d
81.22(6.73)
WB Fat Mass (kg)
(n = 19)
10.70(3.08)
11.05(4.00)
11.03(4.87)
11.35(4.46)
BMI (kg/m2)
(n = 20)
28.65(1.90)
28.62(2.03)
28.49(2.08)
28.67(1.94)
BUA (dB/MHz)
(n = 20)
118.3(15.3)
117.9(16.8)
117.4(16.3)
117.6(15.3)
Tibial Mass at 4% site (g/cm)
(n = 20)
5.55(0.85) 5.55(0.90)
5.52(0.77) 5.59(0.88)
Tibial Mass at 38% site (g/cm)
(n = 19)
5.37(0.53)a,e,f
5.41(0.53)
5.42(0.57)
5.41(0.50)
Leg Bone:Muscle Area, 66%
Site(%) (n=20)
5.33(0.52)a,f
5.51(±0.56) 5.49(0.61) 5.50(0.62)
Leg Fat Area, 66% site (mm2)
(n=20)
1005(590)a
1303(549) 1195(455) 1135(592)
BMD: bone mineral density; BMI: body mass index; BUA: broadband ultrasound attenuation; Dist. R&U BMD: 6
distal radius and ulna BMD; FN BMD: femoral neck BMD; LS BMD: lumbar spine BMD; NS: not significant; 7
Prox. Rad BMD: proximal radius BMD; WB: whole body; a: sig. difference between pre-2009 and mid-2009; 8
b: sig. difference between mid-2009 and post-2009; c: sig. difference between mid-2009 and pre-2010; d: sig. 9
difference between post-2009 and pre-2010; e: sig. difference between pre-2009 and post-2009; f: sig. 10
difference between pre-2009 and pre-2010. 11
12
Only WB BMD changed significantly across the 2009 season (mean difference = 0.021, 13
95%CI = 0.008-0.035 g/cm2, P = 0.01), increasing until mid-season (mean difference = 14
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0.061, 95%CI = 0.054-0.069 g/cm2, P = 0.001) and decreasing thereafter (mean difference =
-1
0.050, 95%CI = -0.060-0.025 g/cm
2, P = 0.001), but remaining higher than 2009 pre-season 2
values (mean difference = 0.010, 95%CI = 0.002-0.019 g/cm2, P = 0.02; Figure 2A). No 3
significant changes were observed for LS or FN BMD over the 12-month period (Figures 2B 4
& C); however changes were evident for forearm BMD. Distal forearm BMD decreased until 5
mid-season (mean difference = -0.007, 95%CI = -0.013-0.001 g/cm
2, P = 0.01; Figure 2D), 6
with a subsequent significant increase from mid- to post-season (mean difference = 0.007, 7
95%CI = 0.002-0.010 g/cm2, P = 0.001), at which time BMD of the proximal radius and ulna 8
also significantly increased (mean difference = 0.007, 95%CI = 0.002-0.014 g/cm2, P = 0.01; 9
Figure 2E). Proximal radius BMD decreased from 2009 post-season to 2010 pre-season 10
(mean difference = -0.010, 95%CI = -0.016-
-0.004 g/cm
2, P = 0.01). 11
No significant changes were observed in tibial mass at the 4% tibial site (P = 0.364). Tibial 12
mass increased at the 14% site over the 12 month period (mean difference = 0.017, 95%CI = 13
0.002-0.031 g/cm2, P = 0.03) and at the 38% site at each time-point relative to pre-season 14
2009 (P ≤ 0.05; Figure 2F). 15
No significant changes were observed in single leg stance or vertical jump measures across 16
the season. 17
Exposure and Injuries 18
Table 3 demonstrates the type and frequency of training sessions performed throughout the 19
2009 season. Pre-season training consisted of a greater focus on strength, skills and 20
conditioning, while a greater emphasis was placed on football drills and between-match 21
recoveries during the latter stages of the season. A total of 29 weekly games were played 22
during the 2009 National Rugby League season, inclusive of three pre-season and two finals 23
matches for a total team game exposure of 501 hours (13 players x 29 games x 1.33 24
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hours).[27] A total of 51 injuries were reported across the 2009 season, equating to an 1
incidence of roughly 101 injuries per 1000 player hours. There were 43 new injuries and 8 2
re-injuries. Twelve injuries occurred when players were running, 21 while being tackled, 4 3
when tackling another player, 1 when kicking, 8 from a collision, 1 from a fall, and 4 were of 4
unknown cause. The players’ dominant sides were affected 45% of the time. Injury types are 5
presented in Table 4. Injuries were classified into one of four categories: bone (fracture or 6
bone bruise), muscle (tear or strain), joint disruption (connective tissue/ligament/tendon 7
injury or dislocation) or impact injury (haematoma/contusion, concussion or rib/sternal 8
injury) and plotted in Figure 3. 9
Table 3. Type and frequency of training sessions performed throughout the 2009 season 10
Type of Training Pre-Season
In-Season
Weeks 1-15
In Season
Weeks 16-26
Number of sessions per week
Team Skills 2-4 0-2 0
Football 0-2 3-4 3-4
Strength 3-4 1-3 1-2
Speed/Power 1-2 1-2 0-1
Conditioning 2 0-2 0-1
Cross Train 1 0-1 0
Recovery 2 2 2-4
11
12
Table 4 Category and frequency of injuries sustained throughout the 2009 season (n = 51) 13
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Type of Injury Category Frequency
Upper Limb
Glenohumeral Joint dislocation
Glenoid Labral lesion
Rotator Cuff impingement
Acromioclavicular Joint sprain
Scapho-lunate Ligament sprain
Carpometocarpal Joint sprain
Metacarpal fracture
Lower Limb
Calcaneal Fat Pad bruise
Lateral Ankle sprain
Syndesmosis sprain
Gastrocnemius contusion
Hamstring strain
Achilles Tendinopathy
Adductor muscle tear
Gastrocnemius tear
Femoral Condyle bruise
Patella bruise
Quadriceps strain
Quadriceps contusion
Lateral knee joint sprain
Patella tendinosis
Fibula bruise
Anterior Cruciate Ligament tear
Head and Torso
Rib Cartilage sprain
Concussion
Sternal bruise
Back contusion
Intercostal muscle strain
3
3
3
3
3
3
1
4
3
3
4
2
3
2
2
1
1
2
4
3
3
1
3
4
4
4
4
2
6
1
1
1
1
1
1
1
5
2
1
7
1
4
2
1
1
3
1
1
1
1
1
2
1
1
1
1
1: Bone-related injury; 2: Muscle-related injury; 3: Joint-related injury; 1
4: Impact-related injury 2
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1
There were no differences in baseline BMI, BUA, WB BMD and BMC, WB lean and fat 2
mass, and tibial mass at the 38% site (P= > 0.05) between injured (n=20) and non-injured 3
(n=16) players. No factor predicted injury incidence or muscle, connective tissue or impact 4
injuries. By contrast, baseline WB BMD, fat mass, lean mass, weight and tibial mass at the 5
38% site accounted for around 53% of the variance in bone-related injuries (R2 = 0.527; P = 6
0.003). 7
8
DISCUSSION 9
Our objective was to examine the anthropometric characteristics of Australian National 10
Rugby League players, pre-, mid- and post season, to determine if relationships exist between 11
those characteristics, and the incidence and type of injuries sustained during a professional 12
season. We found body composition changed throughout the season, with players tending to 13
lose lean mass and gain fat mass as the season progressed. We also observed WB BMD 14
increased until mid-season and decreased thereafter. Body composition elements were 15
largely unrelated to injury incidence and type throughout the season. Only start-of-season 16
WB BMD, fat and lean mass, weight and tibial mass (38% site) contributed to the prediction 17
of bone injury incidence. 18
Soft tissue changes 19
Our observation that players lost lean mass across the season paralleled those of a recent 20
report of body composition changes of English Super League players. However, we did not 21
observe the increase in body fat of that study,[15] or of a skinfold study of adult amateur 22
Australian Rugby League players.[28] 23
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We suggest that the lean mass changes reflect the reduction in players’ strength and 1
resistance training regime from 2-4 sessions per week in the pre-season, to only 0-2 sessions 2
per week during the season, when a greater emphasis was placed on match preparation and 3
physical recovery. Markedly increased playing exposure and intensity, including 4
representative games, had the effect of reducing between-game recovery time such that 5
fatigue, microtrauma and injuries [5, 12, 15] reduce the capacity for fitness and strength 6
training. The implications of the observed lean tissue changes are unclear. It is possible that 7
reductions in lean mass may reduce muscle strength and endurance, speed, agility and power 8
across the course of the season;[1] however the degree of such an effect would be difficult to 9
quantify. 10
11
Bone changes 12
It was not unexpected to find that the average bone mass of the elite rugby league players at 13
each DXA measured site was considerably higher than the “normal” population. The 14
majority of players participating in the current study began playing football prior to, or during 15
their adolescent years, a time when bone is highly responsive to mechanical loading.[29] 16
While it is difficult to differentiate the influence of self-selection (more physically robust 17
individuals tolerating the rigours of rugby league playing at the elite level better than more 18
diminutive individuals) from the osteogenic effect of rugby league playing, the observed 19
seasonal variation in bone mass is informative. The WB BMD gain to mid-season, is likely 20
attributable to the highly favourable pre-season loading stimulus of high intensity fitness and 21
resistance training, coupled with a typically tardy bone remodelling response. The 22
subsequent loss in the latter stages of the season may reflect a relative “detraining” effect on 23
an “over-adapted” skeleton as training time and intensity is dramatically reduced to optimise 24
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game and injury recovery. An increase in WB BMD from preseason 2009 to preseason 2010 1
may be indicative of continued maturational growth in a relatively young cohort that is yet to 2
attain peak bone mass. This observation is especially meaningful in light of the observed 3
bone changes across a playing season suggesting that even the robust skeletons of very highly 4
trained young adult male athletes are sensitive to subtle changes in mechanical loading. 5
6
The current study is the first to examine the baseline and seasonal changes in elite rugby 7
league player bone morphology and volumetric density from pQCT. While the significant 8
increase in proximal tibial mass (38% site) across the season has not previously been 9
observed, we found no relationship between any pQCT parameter and player injury. The 10
lack of observed relationship is potentially related to the small sample size and relatively 11
small number of injuries. Further pQCT data collection is indicated. 12
13
Our results revealed that the average BMI of all players was 29(2.3)kg/m2 Irrespective of 14
position, this value was higher than the recommended BMI guidelines (18.5-25 kg/m2),[14] 15
thereby classifying the cohort as overweight or obese. In this case the metric clearly 16
misrepresents the endomorphic mesomorph physiques of rugby league players.[14] Indeed, 17
our DXA findings indicate that rugby league player body composition is largely comprised of 18
lean mass (average 80.6 kg = 84.9 %) with only a small proportion of fat (average 12.2 kg = 19
8.7 %). Our findings confirm that BMI should not be used to track changes in body 20
composition in mesomorphic athletes.[15] 21
22
Injuries 23
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Joint disruption injuries were the most common injury sustained (Figure 3) which is in partial 1
agreement with previous reports,[2, 5, 30] but not all [9, 11, 12, 31]. Start-of-season 2
anthropometric factors had limited ability to predict injury incidence or type throughout the 3
season. Furthermore, there were no correlations between any anthropometric factors and 4
muscle, connective tissue or impact injuries; however, WB BMD, fat and lean mass, weight 5
and tibial mass at the 38% site were predictive of bone-related injuries. 6
7
Limitations 8
While the total participant numbers in our study are comparable to that of other reports,[15, 9
32] reduced player attendance at 2009 post-season testing somewhat weakened statistical 10
power. The relatively low injury numbers also limited our ability to detect significant 11
associations with risk factors. 12
13
Conclusion 14
We observed an overall loss in lean mass of players throughout a professional rugby league 15
season. This was accompanied by an increase in WB BMD until mid-season, which 16
progressively decreased thereafter. We did not identify any strong relationships between body 17
composition and injuries, with the exception of a relationship between baseline WB BMD, fat 18
and lean mass, weight and tibial mass (38% site) and bone injury incidence. Longer term 19
tracking of rugby league player body composition and injuries is warranted. 20
21
What this study adds 22
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• Rugby league player muscle mass decreases across a professional season, and WB BMD 1
increases until mid-season, decreasing thereafter. 2
• Start of season WB BMD, fat and lean mass, weight and tibial mass (38% site) may be 3
associated with incidence of rugby league player bone injury. 4
5
Acknowledgements The authors would like to thank the staff and players of the Australian 6
National Rugby League team who participated in the study. 7
8
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1
REFERENCES 2
3
1. Meir R. Evaluating players fitness in professional rugby league : reducing 4
subjectivity. Strength Cond Coach 1993;1:11-7. 5
2. Gibbs N. Injuries in professional rugby league: a three-year prospective study of the 6
South Sydney Professional Rugby League Football Club. Am J Sports Med 1993;21:696-700. 7
3. Seward H, Orchard J, Hazard H, et al. Football injuries in Australia at the elite level. 8
Med J Aust 1993;159:298-301. 9
4. Gabbett TJ, Domrow N. Relationships between training load, injury, and fitness in 10
sub-elite collision sport athletes. J Sports Sci 2007;25:1507-19. 11
5. Gabbett TJ, Domrow N. Risk factors for injury in subelite rugby league players. Am J 12
Sports Med 2005;33:428-34. 13
6. Gabbett T, Kelly J, Ralph S, et al. Physiological and anthropometric characteristics of 14
junior elite and sub-elite rugby league players, with special reference to starters and non-15
starters. J Sci Med Sport 2009;12:215-22. 16
7. Gissane C, Jennings D, Kerr K, et al. A pooled data analysis of injury incidence in 17
rugby league football. Sports Med 2002;32:211-6. 18
8. Phillips LH, Standen PJ, Batt ME. Effects of seasonal change in rugby league on the 19
incidence of injury. Br J Sports Med 1998;32:144-8. 20
9. Stephenson S, Gissane C, Jennings D. Injury in rugby league: a four year prospective 21
survey. Br J Sports Med 1996;30:331-4. 22
10. King DA, Gabbett TJ, Gissane C, et al. Epidemiological studies of injuries in rugby 23
league: suggestions for definitions, data collection and reporting methods. J Sci Med Sport 24
2009;12:12-9. 25
Page 22 of 31
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jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2012-001400 on 6 N
ovember 2012. D
ownloaded from
For peer review only
23
11. Gabbett TJ. Severity and cost of injuries in amateur rugby league: a case study. J 1
Sports Sci 2001;19:341-7. 2
12. Gabbett TJ. Incidence, site, and nature of injuries in amateur rugby league over three 3
consecutive seasons. Br J Sports Med 2000;34:98-103. 4
13. Meir R. Seasonal changes in estimates of body composition in professional rugby 5
league players. Sport Health 1993;11:27-31. 6
14. Lundy B, O'Connor H, Pelly F, et al. Anthropometric characteristics and competition 7
dietary intakes of professional rugby league players. Int J Sport Nutr Exerc Metab 8
2006;16:199-213. 9
15. Harley JA, Hind K, O'Hara JP. Three-compartment body composition changes in elite 10
rugby league players during a super league season, measured by dual-energy X-ray 11
absorptiometry. J Strength Cond Res 2011;25:1024-9. 12
16. Van der Ploeg GE, Withers RT, Laforgia J. Percent body fat via DEXA: comparison 13
with a four-compartment model. J App Phys 2003;94:499-506. 14
17. Haapasalo H, Kontulainen S, Sievänen H, et al. Exercise-induced bone gain is due to 15
enlargement in bone size without a change in volumetric bone density: a peripheral 16
quantitative computed tomography study of the upper arms of male tennis players. Bone 17
2000;27:351-7. 18
18. Sawada K, Morishige K, Ohmichi M, et al. Peripheral quantitative computed 19
tomography (pQCT) is useful for monitoring bone mineral density of the patients who 20
receive hormone replacement therapy. Maturitas 2007;56:343-9. 21
19. Schoenau E, Neu CM, Rauch F, et al. The development of bone strength at the 22
proximal radius during childhood and adolescence. J Clin Endocrinol Metab 2001;86:613-8. 23
Page 23 of 31
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
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rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2012-001400 on 6 N
ovember 2012. D
ownloaded from
For peer review only
24
20. Tsurusaki K, Ito M, Hayashi K. Differential effects of menopause and metabolic 1
disease on trabecular and cortical bone assessed by peripheral quantitative computed 2
tomography (pQCT). Br J Radiol 2000;73:14-22. 3
21. Giles GC, Ireland PD. Dietary Questionnaire for Epidemiological Studies (Version 2). 4
Melbourne: The Cancer Council Victoria; 1996. 5
22. Weeks BK, Beck BR. The BPAQ: a bone-specific physical activity assessment 6
instrument. Osteoporos Int 2008;19:1567-77. 7
23. Beck BR, Weeks BK. Which limb to scan? Revisiting the relationship between 8
functional and skeletal limb dominance. J Bone Miner Res 2010;25. 9
24. Guskiewicz KM, Perrin DH. Research and clinical applications of assessing balance. J 10
Sport Rehab 1996;5:45-63. 11
25. Cochrane DJ, Stannard SR. Acute whole body vibration training increases vertical 12
jump and flexibility performance in elite female field hockey players. Br J Sports Med 13
2005;39:860-5. 14
26. Gabbett TJ. Incidence of injury in amateur rugby league sevens. Br J Sports Med 15
2002;36:23-6. 16
27. King T, Jenkins D, Gabbett T. A time-motion analysis of professional rugby league 17
match-play. J Sports Sci 2009;27:213-9. 18
28. Gabbett TJ. Changes in physiological and anthropometric characteristics of rugby 19
league players during a competitive season. J Strength Cond Res 2005;19:400-8. 20
29. Ginty F, Rennie KL, Mills L, et al. Positive, site-specific associations between bone 21
mineral status, fitness, and time spent at high-impact activities in 16- to 18-year-old boys. 22
Bone 2005;36:101-10. 23
30. Gabbett TJ. Influence of the limited interchange rule on injury rates in sub-elite rugby 24
league players. J Sci Med Sport 2005;8:111-5. 25
Page 24 of 31
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25
31. Gabbett. Incidence of injury in semi-professional rugby league players. Br J Sports 1
Med 2003;37:36-43. 2
32. Elloumi M, Ben Ounis O, Courteix D, et al. Long-term rugby practice enhances bone 3
mass and metabolism in relation with physical fitness and playing position. J Bone Miner 4
Metab 2009;27:713-20. 5
6
7
8
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FIGURE LEGENDS 1
2
Figure 1 Change in percent lean (A) and percent fat (B) of players measured at all testing 3
time points (n=19). ( * Significantly different from baseline; ∆ Significant change between time points). 4
5
Figure 2 Seasonal change in whole body (A; n=19), lumbar spine (B; n=20), femoral neck 6
(C; n=19), distal radius (D; n=18) and proximal radius (E; n=18) bone mineral density 7
(BMD) and tibial bone mass (F) at 4% (n=20) and 38% (n=19) sites of professional rugby 8
league players. (* Significantly different from baseline; ∆ Significant change between time points). 9
10
Figure 3 Frequency distribution by injury category of professional rugby league players 11
across a playing season (n=37) 12
13
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201x74mm (300 x 300 DPI)
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206x217mm (300 x 300 DPI)
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Frequency distribution by injury category of professional rugby league players across a playing season (n=37)
157x122mm (300 x 300 DPI)
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STROBE 2007 (v4) Statement—Checklist of items that should be included in reports of cohort studies
Section/Topic Item
# Recommendation Reported on page #
Title and abstract 1 (a) Indicate the study’s design with a commonly used term in the title or the abstract 1
(b) Provide in the abstract an informative and balanced summary of what was done and what was found 3
Introduction
Background/rationale 2 Explain the scientific background and rationale for the investigation being reported 5
Objectives 3 State specific objectives, including any prespecified hypotheses 6
Methods
Study design 4 Present key elements of study design early in the paper 7
Setting 5 Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow-up, and data
collection
7
Participants 6 (a) Give the eligibility criteria, and the sources and methods of selection of participants. Describe methods of follow-up 7
(b) For matched studies, give matching criteria and number of exposed and unexposed N/A
Variables 7 Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers. Give diagnostic criteria, if
applicable
7-10
Data sources/
measurement
8* For each variable of interest, give sources of data and details of methods of assessment (measurement). Describe
comparability of assessment methods if there is more than one group
7-11
Bias 9 Describe any efforts to address potential sources of bias N/A
Study size 10 Explain how the study size was arrived at 7
Quantitative variables 11 Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen and
why
11
Statistical methods 12 (a) Describe all statistical methods, including those used to control for confounding 11
(b) Describe any methods used to examine subgroups and interactions 11
(c) Explain how missing data were addressed N/A
(d) If applicable, explain how loss to follow-up was addressed N/A
(e) Describe any sensitivity analyses N/A
Results
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Participants 13* (a) Report numbers of individuals at each stage of study—eg numbers potentially eligible, examined for eligibility, confirmed
eligible, included in the study, completing follow-up, and analysed
11,12,13 (Table 2)
(b) Give reasons for non-participation at each stage 11
(c) Consider use of a flow diagram N/A
Descriptive data 14* (a) Give characteristics of study participants (eg demographic, clinical, social) and information on exposures and potential
confounders
11-12
(b) Indicate number of participants with missing data for each variable of interest Table 2 page 12
(c) Summarise follow-up time (eg, average and total amount) 7
Outcome data 15* Report numbers of outcome events or summary measures over time 11-16
Main results 16 (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision (eg, 95% confidence
interval). Make clear which confounders were adjusted for and why they were included
12-16
(b) Report category boundaries when continuous variables were categorized N/A
(c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time period N/A
Other analyses 17 Report other analyses done—eg analyses of subgroups and interactions, and sensitivity analyses N/A
Discussion
Key results 18 Summarise key results with reference to study objectives 16
Limitations
Interpretation 20 Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from
similar studies, and other relevant evidence
19
Generalisability 21 Discuss the generalisability (external validity) of the study results 19
Other information
Funding 22 Give the source of funding and the role of the funders for the present study and, if applicable, for the original study on
which the present article is based
20
*Give information separately for cases and controls in case-control studies and, if applicable, for exposed and unexposed groups in cohort and cross-sectional studies.
Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published examples of transparent reporting. The STROBE
checklist is best used in conjunction with this article (freely available on the Web sites of PLoS Medicine at http://www.plosmedicine.org/, Annals of Internal Medicine at
http://www.annals.org/, and Epidemiology at http://www.epidem.com/). Information on the STROBE Initiative is available at www.strobe-statement.org.
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