The Relationship between Anthropometric Variables and Isokinetic Strength in a Women’s Collegiate Soccer Team

  Paul A. Burkett, Shawn D. Felton, Mitchell L. Cordova, FACSM Sports Medicine Research Laboratory, Department of Rehabilitation Sciences, Florida Gulf Coast University, Fort Myers, FL USA

Abstract

Introduction

Methods

Results

Discussion

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This study examined the relationship between common anthropometric variables and average torque production of the knee extensors measured by isokinetic testing at three angular velocities in a women’s collegiate soccer teamThe subjects tested were members of a NCAA Division I women’s soccer team. This group went on to win the conference regular season and conference tournament championships, and advance to the second round of the NCAA national tournament. These outcomes suggest that the subjects were highly skilled athletes in their sport. Previous studies involving highly skilled female athletes suggested that measures such as percent body fat 7,9 and skeletal muscle mass 9 were not strong predictors of anaerobic power and jumping performance. The same may be true of the relationship between anthropometric measures and isokinetic knee strength in highly skilled female athletes. The results found in this group of highly skilled female athletes differ from previous research involving physically active female non-athletes of a similar age. Anthropometric measures have been reported to be related to isokinetic knee strength in physically active female non-athlete. 4 The subjects in this study represent a more heterogeneous athletic population than found in the general population.

Isokinetic testing is widely utilized by clinicians to evaluate lower extremity strength and as a tool to assist in treatment decisions. 1 Previous research has demonstrated its efficacy and reliability in muscle training and clinical evaluation of muscular performance. 2 Research has also suggested that isokinetic force production is associated with sports related performance. For example, It has been suggested that isokinetic force production in the legs could be used to evaluate and predict on-ice skating speed and skating power in men’s intercollegiate ice hockey players. 3 Prior research also has investigated the relationship between strength output and anthropometric measurements such as BMI and body fat percentage. The conclusions concerning these relationships have been inconsistent. Knee isokinetic strength was reported to be significantly negatively correlated with the percentage of body fat and positively correlated with fat free mass in college students who were not competitive athletes. 4 In young male competitive soccer players ages 10 to 17 years, certain anthropometric measures were related to isokinetic strength for both knee extensors and flexors, with 73-93% of the variance explained by using combinations of age, body mass, percentage of body fat, and hours training per week. 5 Body mass was the main independent variable that explained variance, which was in agreement with a previous study. 6 Fat free mass, but not percent body fat, was reported to be related to anaerobic power in male and female elite young wrestlers. 7 However, percent body fat was found to be related to on-ice skating speed and skating power in men’s intercollegiate ice hockey players. 3 In contrast, lean body mass, percentage of fat tissue, and percentage of muscle tissue were reported to be poor predictors of sprinting performance in well-conditioned males. 8 Percent body fat and percent skeletal muscle mass were found to be strong predictors of jumping performance in female non-athletes, but were not as strongly related to jumping performance in elite female athletes. 9 The inconsistent findings concerning the relationship between strength output and anthropometric measurements such as BMI and body fat percentage suggest that the strength of the relationship may vary depending on the population studied. The purpose of this study was to investigate the relationship between common anthropometric variables and average torque production of the knee extensors measured by isokinetic testing at three angular velocities in a women’s collegiate soccer team.

•  Pearson Bivariate Correlations presented in Table. 2

•  Hierarchical linear regression analysis was used to test if anthropometric measurements predicted isokinetic average peak torque at 300°/sec. The results of the regression indicated the three predictors (BMI, LBMI, & % Body Fat explained 33.3% of the variance (R2 = .33, F(3, 24) = 3.994, P = .019. Table 3. However the t-test for each predictor was not significant due to the highly correlated variables.

•  A significant moderate positive correlation between average peak torque and BMI (.408 to .449 P < 0.5 and .557; P <.001), Lean body mass (.404 to .425; P < 0.5), and LBMI (.376 to .413; P <.05)

•  The level of significance was established at P <0.05.

Knee isokinetic strength has been reported to be correlated with body fat, fat free mass, and BMI in college students. It is unclear if these anthropometric variables are related to isokinetic performance in relatively homogeneous groups of athletes. PURPOSE: To investigate the relationship between common anthropometrics and average torque production of the knee extensors in a women’s collegiate soccer team. METHODS: Twenty-eight healthy female collegiate soccer athletes aged 18-22 years participated. The participants had no history of significant lower leg injuries. Participants were screened using standard anthropometric measurements that included: height, weight, and skinfold measures of the triceps, suprailiac, and thigh areas. The measurements allowed for calculation of the BMI, lean body mass, lean body mass index (LBMI), and body fat percentage. Isokinetic strength of knee flexion and extension was measured through three angular velocities of 60, 180, and 300 degrees/sec. The relationships between the anthropometric measurements (height, weight, BMI, lean body mass, LBMI, body fat percentage) and average peak torques at the three angular velocities were assessed utilizing hierarchal linear regression and bivariate correlation coefficients. RESULTS: Hierarchal linear regression revealed a significant relationship for average peak torque at 300 degrees/sec with BMI, lean body mass index, and body fat as the predictors, (F (3, 24)=4.0, P = .019), . Further analysis utilizing Pearson’s bivariate correlation coefficient matrix found moderate correlations between average peak torque and BMI (.408 to .557; P<.05), lean body mass (.404 to .425; P<.05), and LBMI (.376 to .413; P<.05). CONCLUSION: The results found in this athletic population differ from previous research involving physically active non-athletes of a similar age. While anthropometric measures have been reported to be related to isokinetic knee strength in non-athletes, in this athletic population the relationship varied depending on the angular velocity. The results suggest that anthropometric measurements such as height, weight, BMI, lean body mass, LBMI, and body fat percentage may not be strong predictors of isokinetic knee muscle strength across angular velocities in an athletic population.

Subjects: Twenty-eight healthy female collegiate soccer athletes (mean: age 19.57, height 166.04 cm ± 20.88 cm, mass 62.10 kg ±1.16 kg ) volunteered for this study. The anthropometric measurements of interest and isokinetic strength measures were collected during routine pre-season athlete evaluations. No informed consent was needed because all athletes signed a medical release document releasing medical professionals to examine and share information while protecting their specific anonymity. This study was approved by the University institutional review board. Methods: Anthropometric measures were obtained including height, mass, and skinfold thickness. Skinfold measures were taken at three sites: triceps, suprailiac, and thigh. The sum of the skinfolds was used to estimate percent body fat and lean body mass (LBM) using equations specific for gender and age (2). Body mass was measured to the nearest 0.01 kg with participants clothed in shorts and tee shirts using digital scales (Healthometer). Height was measured to the nearest 0.01 cm with participants barefoot using a wall-mounted stadiometer (Heightronics, QuickMedical, Issaquah, USA). Body mass index (BMI, kg/m2) and lean body mass index (LBMI, kg/m2) were calculated. The athletes participated in a lower extremity warm-up and then Isokinetic strength of knee flexion and extension was measured through three angular velocities of 60°, 180°, and 300°/sec. Figure 1. Statistical Analysis: •  Descriptive Statistics Table 1 were calculated for all anthropometric

measurements and average peak torques of the bi-lateral thigh musculature at 60°, 180°, & 300°/sec.

•  Hierarchical linear regression utilized for prediction due to the hierarchical nature of the data set.

Height Weight Age Body Fat BMI Lean Mass

LBMI 60 Avg. Peak Torque - R

180 Avg. Peak Torque - R

300 Avg. Peak Torque - R

60 Avg. Peak Torque -- L

180 Avg. Peak Torque -- L

300 Avg. Peak Torque

-- L Height 1

Weight .525** 1

Age -.223 -.223 1

Body Fat .107 .107 .223 1 ** sig at 0.01

BMI .040 -.199 .282 .342 1 * sig at 0.05

Lean Mass .226 .413* -.028 .171 .318 1

LBMI .220 -.433* .209 -.194 .821** .296 1

60 Avg. Peak Torque - R .566** .059 -.002 -.061 .362 .425* .413* 1

180 Avg. Peak Torque - R .364 .129 .253 .262 .408* .404* .265 .791** 1

300 Avg. Peak Torque - R .143 .157 .195 .192 .105 .280 .011 .520** .790** 1

60 Avg. Peak Torque - L .198 .131 .020 -.069 .308 .246 .312 .610** .497** .314 1

180 Avg. Peak Torque - L .138 .107 .374 .115 .449* .347 .377* .570** .650** .437* .874** 1

300 Avg. Peak Torque -L .164 .109 .528** .332 .557** .423* .376* .512**

.697** .594** .623** .782** 1

Figure 1. Isokinetic Knee Testing

Mean Std. Deviation N Height (cm)   166.04 20.88 28 Mass (kg)   62.10 1.16 28 Age   19.57 1.23 28 % Body Fat   24.41 2.98 28 BMI   22.25 1.58 28 Lean Mass   103.29 6.12 28 LBMI   16.86 1.05 28 Avg Peak Torque 60 R   101.97 16.34 28 Avg Peak Torque 180 R   66.78 9.32 28 Avg Peak Torque -300 R   47.46 6.63 28 Avg Peak Torque 60 L   98.57 15.89 28 Avg Peak Torque 180 L   66.40 8.97 28 Avg Peak Torque -300 L   48.86 5.85 28

a.  Dependent Variable: Avg. Peak Torque 300

b.  Predictors: (Constant), BMI

c.  Predictors: (Constant), BMI, LBMI

d.  Predictors: (Constant): BMI, LBMI, Body Fat

Table. 2 Pearson Correlations Between Anthropometric Measurements and Quadriceps Isokinetic Torque Production

Table. 1 Means and SD of Observed Variables

Table. 3. ANOVA for Predictors of Avg. Peak Torque at 300 degrees/sec

Summary •  The results of this study were inconsistent in that the strength of the

relationship varied depending on the angular velocity and limb being tested. Significant relationships were found only at 300°/sec, with BMI, lean body mass index, and body fat as the predictors of average peak torque of the quadricep muscles.

•  The results further suggested anthropometric measurements such as height, weight, BMI, lean body mass, LBMI, and body fat percentage may not be strong predictors of isokinetic knee muscle strength across angular velocities in highly skilled women’s soccer athletes.

Model Sum of Sqaures

df Mean Square

F Sig.

1 Regression 285.91 1 285.91 11.67 .002 Residual 636.96 26 24.5

Total 922.86 27 2 Regression 304.5 2 152.25 6.16 .007

Residual 618.37 25 24.74 Total 922.86 27

3 Regression 307.33 3 102.44 3.99 .019 Residual 615.53 24 25.65

Total 922.86 27