electromyographic analysis of traditional and non traditional abdominal exercises

8/10/2019 Electromyographic Analysis of Traditional and Non Traditional Abdominal Exercises

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The hanging knee-up with straps exercise started andended with the arms supported within the straps, theshoulders and elbows flexed approximately 90 degrees,and the body hanging in a vertical position with thetrunk, hips, and knees in full extension. From thisposition, the subject maximally flexed the hips, resultingin 125 to 135 degrees of hip and knee flexion and aposteriorly tilted pelvis (Fig. 2). A tester maintained 1hand on the lumbar spine throughout the movement toprevent the body from swaying back and forth.

The Power Wheel pike and power wheel knee-up exer-cises started and ended with the subject in the push-upposition (trunk, hips, knees, and elbows in full exten-sion, shoulders flexed 90, and hands on the floorapproximately a shoulder width apart), the feet abovethe floor and attached to Power Wheel straps, and thewheel in a vertical position on the floor (Figs. 3A and3B). For the Power Wheel pike, from the starting posi-tion the wheel was rolled toward the hands as the subjectperformed a body pike by maximally flexing the hips

Figure 1.Abdominal exercises. (A) Ab Revolutionizer double crunch, (B) Ab Revolutionizer oblique crunch, (C) Ab Revolutionizer reverse crunch, (D) Ab

Revolutionizer reverse crunch with weights.

Physical Therapy . Volume 86 . Number 5 . May 2006 Escamilla et al . 659


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(resulting in 110120 of hip flexion and a posteriorlytilted pelvis) while maintaining an extended-knee posi-tion (Fig. 3A). For the Power Wheel knee-up, from the

starting position the wheel was rolled toward the handsas the subject maximally flexed the hips and knees(resulting in 125135 of hip and knee flexion and aposteriorly tilted pelvis) (Fig. 3B).

The Power Wheel roll-out exercise started and ended inthe quadruped position (on hands and knees with hipsand shoulders flexed approximately 90) with a neutralspine and pelvis. From this position, the subject straight-ened out the body by rolling forward in a straight linewhile maintaining a neutral spine and pelvis (Fig. 3C).

The reverse crunch flat and reverse crunch inclined 30degrees started and ended in the supine position on aflat surface (reverse crunch flat) or on a surface inclined30 degrees from horizontal (reverse crunch inclined30), with hips and knees flexed approximately 90degrees and the arms positioned as shown in Figure 4.From this starting position, the subject maximally flexedthe hips (resulting in 125135 of hip and knee flexionand a posteriorly tilted pelvis) (Fig. 4).

The crunch and bent-knee sit-up exercises started andended in a supine position with the thumbs positionedin the ears, the hands relaxed against the head, the

knees flexed approximately 90 degrees, and the hipsflexed approximately 45 degrees. During the crunch, thesubject flexed the trunk by performing a curling-upmotion until both scapulae were off the floor (Fig. 5).During the bent-knee sit-up, the feet were supported,and the subject simultaneously flexed the trunk and hipsuntil the elbows were even with the knees (Fig. 6).

ProcedureAll subjects became familiar with and practiced allabdominal exercises during a pretesting session thattook place approximately 1 week before the testingsession. During this time, each subject received instruc-tional sessions explaining how to perform each of theabdominal exercises correctly (each abdominal devicecame with written or video instructions for its use). Allexercises were performed with a 3-second cadence(1 second from start of exercise to end range, 1-secondisometric hold at end range, 1 second to return tostarting position) and a 1-second rest between repeti-

tions. The subjects practiced multiple repetitions foreach exercise under the supervision of trained researchpersonnel. A metronome (set at 1 beat per second) wasused to help ensure proper cadence during both thepretesting and the testing sessions. Once a subject wasable to perform each exercise correctly with the propercadence, a testing session was scheduled.

Blue Sensor disposable surface electrodes (type M-00-S)were used to collect EMG data. These oval electrodes(22 mm wide and 30 mm long) were placed in a bipolarelectrode configuration along the longitudinal axis of a

muscle, with a center-to-center distance of approxi-mately 3 cm between electrodes. Before the electrodeswere positioned over each muscle, the skin was preparedby shaving, abrading, and cleaning with isopropyl alco-hol wipes to reduce skin impedance values, which typi-cally were 10 k. Electrode pairs then were placed onthe subjects right side (except for the internal obliquemuscle electrode pair, which was positioned on thesubjects left side because the rotational function of theinternal oblique muscle is opposite that of the externaloblique muscle) for the following muscles in accordancewith procedures previously described1619:

(1) upper rectus abdominispositioned vertically andcentered on the muscle belly (not on the tendinousintersection) near the midpoint between the umbi-licus and the xiphoid process and 3 cm lateral fromthe midline;

(2) lower rectus abdominispositioned 8 degrees fromvertical in the inferomedial direction and centeredon the muscle belly near the midpoint between the

Ambu Inc, 611 N Hammonds Ferry Rd, Linthicum, MD 21090-1356.

Figure 2.Abdominal exercise. Hanging knee-up with straps.

660 . Escamilla et al Physical Therapy . Volume 86 . Number 5 . May 2006


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umbilicus and the pubic symphysis and 3 cm lateralfrom the midline;

(3) external obliquepositioned obliquely approxi-mately 45 degrees (parallel to a line connecting themost inferior point of the costal margin of the ribsand the contralateral pubic tubercle) above theanterior superior iliac spine (ASIS) at the level ofthe umbilicus;

(4) internal obliquepositioned horizontally 2 cminferomedial to the ASIS within a triangle outlinedby the inguinal ligament, the lateral border of therectus sheath, and a line connecting the ASISs;

(5) latissimus dorsipositioned obliquely (approxi-mately 25 from horizontal in the inferomedialdirection) 4 cm below the inferior angle of thescapula;

(6) rectus femorispositioned vertically near the mid-line of the thigh, approximately halfway between theASIS and the proximal patella; and

(7) lumbar paraspinalpositioned vertically 3 cm lat-eral to the spine and near the level of the iliac crestbetween the L3 and L4 vertebrae. A ground (refer-ence) electrode was positioned over the skin of theright acromion. Electrode cables were connected to

the electrodes and taped to skin appropriately tominimize pull on the electrodes and movement ofthe cables.

Once the electrodes were positioned, the subjectwarmed up and practiced the exercises as needed, andthen data collection commenced. The EMG data werecollected by use of a Myosystem EMG unit. The ampli-fier bandwidth frequency was 10 to 500 Hz, with an input

Noraxon USA Inc, 13430 N Scottsdale Rd, Suite 104, Scottsdale, AZ 85254.

Figure 3.Abdominal exercises. (A) Power Wheel pike, (B) Power Wheel knee-up, (C) Power Wheel roll-out.



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voltage of 12 V (direct current) at 1.5 A.The input impedance of the amplifier

was 20,000 k

, and the common-moderejection ratio was 130 dB. The EMGdata were sampled at 1,000 Hz, and therecorded signals were processedthrough an analog-to-digital converterby use of a 16-bit analog-to-digitalboard.

The EMG data were collected during 5repetitions of each exercise, with allexercises being performed in a ran-domized order. Each repetition wasperformed in a slow and controlled

manner with the 3-second cadence pre-viously described and a 1-second restbetween repetitions. With the relativelysmall number of repetitions per-formed, all subjects acknowledged thatfatigue was minimal. A testing sessiontook 30 to 45 minutes to complete.

Randomly interspersed within the exer-cise testing session, EMG data fromeach muscle tested were collected dur-ing two 5-second maximum voluntary

Figure 4.Abdominal exercises. (A) Reverse crunch flat, (B) Reverse crunch inclined 30 degrees.

Figure 5.Abdominal exercise. Bent-knee sit-up.



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isometric contractions (MVICs). After conducting pilotwork, we adopted for MVIC testing the following proto-cols, which were based on the positions that elicited thehighest MVIC for each respective muscle (all MVICs

were collected on a plinth with the subject in a prone,supine, or short sitting position):

(1) upper and lower rectus abdominis body supinewith hips and knees flexed 90 degrees, feet sup-ported, and trunk maximally flexed (ie, curl-upposition), with resistance at the shoulders in thetrunk extension direction;

(2) external and internal obliquebody supine withhips and knees flexed 90 degrees, feet supported,and trunk maximally flexed and rotated to the left,

with resistance at the shoulders in the trunk exten-sion and right rotation directions;

(3) latissimus dorsibody prone with right shoulderabducted 0 degrees and extended maximally, withresistance at the right distal arm in the direction ofshoulder flexion;

(4) lumbar paraspinalbody prone with trunk fullyextended and hands clasped behind head, withresistance at the shoulders in the direction of trunkflexion; and

(5) rectus femorisbody in short sitting position withhips and knees flexed 90 degrees, with resistance atthe distal leg in the knee flexion direction.

The MVICs were collected to normalize the EMG datafrom the abdominal exercises in order for the activity ofa muscle during exercise to be compared with theactivity of that same muscle during MVIC. Subjects weregiven similar verbal encouragements for each of theMVICs to help ensure a maximum effort throughout the5-second duration, and the subjects was asked after each

MVIC if they thought it required max-imum effort. If not, the MVIC wasrepeated. Approximately 1 minute ofrest was given between the MVICs,and approximately 2 minutes of restwere given between the exercise trials.

Data ProcessingRaw EMG signals were full-wave recti-fied, smoothed with a 10-millisecondmoving average window, and thenaveraged over the entire duration ofeach exercise repetition or MVIC per-formed. For each repetition, the EMGdata were normalized for each muscleand expressed as a percentage of the

EMG data for a subjects highest corresponding MVICtrial, determined by calculating throughout the 5-secondMVIC the highest average EMG signal over a 1-secondinterval. Normalized EMG data then were averaged over

the 5 repetition trials performed for each exercise andused in statistical analyses.

Data AnalysisA 1-factor, repeated-measures analysis of variance wasused to assess differences in normalized EMG muscleactivity among the different exercise variations, and posthocanalyses were performed with the Bonferroni test toevaluate the significance of between-exercise pair-wisecomparisons. The significance level was set atP.01.

Results

Normalized EMG data for each muscle and exercise areshown in Table 2. Among all exercises tested, upperrectus abdominis muscle EMG activity was highest forthe Power Wheel roll-out, hanging knee-up with straps,and reverse crunch inclined 30 degrees and lowest forthe Ab Revolutionizer reverse crunch. Lower rectusabdominis muscle EMG activity was highest for thePower Wheel roll-out and hanging knee-up with strapsand lowest for the Ab Revolutionizer reverse crunch.Graphical representations of upper and lower rectusabdominis muscle activity ranked from highest to lowestamong all exercises are shown in Figures 7 and 8.

External oblique muscle EMG activity was highest for thePower Wheel pike, Power Wheel knee-up, and hangingknee-up with straps and lowest for the crunch. Internaloblique EMG activity was highest for the Power Wheelroll-out, Power Wheel pike, Power Wheel knee-up, hang-ing knee-up with straps, and reverse crunch inclined 30degrees and lowest for the 7 remaining exercises. Graph-ical representations of external and internal obliquemuscle activity ranked from highest to lowest among allexercises are shown in Figures 9 and 10.

Figure 6.Abdominal exercise. Crunch.



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Table2.

Electromyographic(EMG)ActivityforEachMuscleandExerciseExpressedasaPercentageoftheMaximumIsometricVolunta

ryContraction

Exercise

Muscle

UpperRectus

Abdominis*

LowerR

ectus

Abdominis*

External

Obliques*

Inte

rnal

Obliques*

Latissimus

Dorsi*

Lumbar

Paraspin

als*

Rectus

Femoris*

PowerWheelroll-out

7626

8129

6427b

66

25

157b,c,f

52b,c,d,e

64b,c,d,e,h,i

PowerWheelpike

4111a,d,e,g

5316a,d

9632

83

31

2716

83

2611c

PowerWheelknee-up

4118a,d,e,g

4512a,d

8030

72

32

2512

84

4318

Hangingknee-upwithstraps

6921

7516

7925

85

40

2112

73

158b,c

Reversecrunchinclined30

7727

5313a,d

5019b,c,d

86

37

148b,c,f

84

2212c

Reversecrunchflat

4120a,d,e,g

3013a,b,c,

d,e,g

3916a,b,c,d

52

24b,c,d,e

2314

63b,c,e

115b,c,e,h

Crunch

5617a,e

4813a,d

2716a,b,c,d,e,h,i,k

42

10b,c,d,e

53a,b,c,d,e,f

31b,c,d,e

,f,h,i

33b,c,d,e,h,i

Bent-kneesit-up

399a,d,e,g

3811a,b,d,e

5016b,c,d

49

22b,c,d,e

63a,b,c,d,f

63b,c,e

2212c

AbRevolutionizerreversecrunchwithweights

4418a,d,e

4017a,b,d,e

5524b,c,d

51

22b,c,d,e

42a,b,c,d,e,f

63b,c,e

1613b,c

AbRevolutionizerdoublecrunch

5317a,e

4016a,b,d,e

3418a,b,c,d,i

51

25b,c,d,e

42a,b,c,d,e,f

42b,c,d,e

,f,h,i

76b,c,d,e,h,i

AbRevolutionizerobliquecrunch

4914a,d,e

3912a,b,d,e

4920b,c,d

48

25b,c,d,e

73a,b,c,d,f

42b,c,d,e

,f,h,i

55b,c,d,e,h,i

AbRevolutionizerreversecrunch

3013a,d,e,g,i,j,k

2410a,b,c,

d,e,g,h,i,j,k

3816a,b,c,d

33

19b,c,d,e

32a,b,c,d,e,f

42b,c,d,e

,f,h,i

65b,c,d,e,h,i

*Therewasasignificantdifference(P.001)inEMGactivityamongtheabdominalexercise

s.

Pair-wisecomparisons(P.01):

aSignificantlylessEMGactivitythanobtained

withthePowerWheelroll-out.

bSignificantlylessEMGactivitythanobtained

withthePowerWheelpike.

cSignificantlylessEMGactivitythanobtained

withthePowerWheelknee-up.

dSignificantlylessEMGactivitythanobtained

withthehangingknee-upwithstraps.

eSignificantlylessEMGactivitythanobtained

withthereversecrunchinclined30degrees.

fSignificantlylessEMGactivitythanobtained

withthereversecrunchflat.

gSignificantlylessEMGactivitythanobtained

withthecrunch.

hSignificantlylessEMGactivitythanobtained

withthebent-kneesit-up.

iSignificantlylessEMGactivitythanobtained

withtheAbRevolutionizerreversecrunchwith

weights.

jSignificantlylessEMGactivitythanobtained

withtheAbRevolutionizerdoublecrunch.

kSignificantlylessEMGactivitythanobtained

withtheAbRevolutionizerobliquecrunch.

lSignificantlylessEMGactivitythanobtained

withtheAbRevolutionizerreversecrunch.



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Latissimus dorsi muscle EMG activity was highest for thePower Wheel pike, Power Wheel knee-up, hangingknee-up with straps, and reverse crunch flat and lowest

for the crunch, Ab Revolutionizer double crunch, AbRevolutionizer reverse crunch, and Ab Revolutionizerreverse crunch with weights. Lumbar paraspinal muscleEMG activity was highest for the Power Wheel pike,Power Wheel knee-up, hanging knee-up with straps, andreverse crunch inclined 30 degrees and lowest for thecrunch, Ab Revolutionizer double crunch, Ab Revolu-tionizer reverse crunch, and Ab Revolutionizer obliquecrunch. Rectus femoris muscle EMG activity was highestfor the Power Wheel knee-up and lowest for the PowerWheel roll-out, crunch, Ab Revolutionizer doublecrunch, Ab Revolutionizer reverse crunch, and Ab Rev-olutionizer oblique crunch.

Discussion

Biomechanical Differences Between Trunk Flexion andExtension ExercisesUnderstanding biomechanical differences between exer-cises is important because trunk flexion, like that used intraditional exercises, such as the crunch or bent-kneesit-up, may be a contraindication or precaution in cer-tain populations (eg, those with lumbar disk pathologiesor osteoporosis). In such individuals, it may be morebeneficial to maintain a neutral pelvis and spine, like

that used in the Power Wheel roll-out, than to useforceful flexion of the lumbar spine, like that used in thebent-knee sit-up. In contrast, some people with facet

joint pain, spondylolisthesis, and vertebral or interverte-bral foramen stenosis may not benefit from exercisesthat maintain the spine and pelvis in a neutral orextended position, because these exercises may contrib-ute to spinal cord or nerve root compression. However,trunk flexion exercises, such as the crunch or reversecrunch, may decrease facet joint pain and increasevertebral or intervertebral foraminal openings, decreas-ing the risk of spinal cord or nerve root impingement.

Although the Power Wheel roll-out and hangingknee-up with straps were both effective in activatingabdominal musculature, these 2 exercises were per-formed in different manners. During the roll-out por-tion of the Power Wheel roll-out exercise, the abdominalmusculature contracts eccentrically or isometrically toresist the attempt of gravity to extend the trunk androtate the pelvis. During the return motion, the abdom-inal musculature contracts concentrically or isometri-cally. If the pelvis and spine are stabilized and main-tained in a neutral position throughout the roll-out andreturn movements, then the abdominal musculaturecontracts primarily isometrically. While subjects wereperforming the roll-out exercise, a relatively neutralpelvis and spine were maintained throughout the move-

Figure 7.Upper rectus abdominis muscle normalized electromyographic (EMG) activity (mean SD) among exercises. MVICmaximum voluntary isometriccontraction, degdegrees, Ab RevAb Revolutionizer, Wtsweights.



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ments. In contrast, during the hanging knee-up exercisewith straps, the abdominal musculature contracts con-centrically initially as the hips flex, the pelvis rotatesposteriorly, and the lumbar spine is flattened and movestoward lumbar flexion. As the knees are lowered and thehips are extended, the reverse movements occur, andthe abdominal musculature contracts eccentrically tocontrol the rate of return to the starting position.

The hanging knee-up with straps exercise and the PowerWheel pike and Power Wheel knee-up exercises all wereperformed similarly by flexing the hips, posteriorly ro-tating the pelvis, and flattening the lumbar spinebasically the reverse of what occurs during the crunchand bent-knee sit-up exercises, which involve trunkflexion followed by hip flexion (bent-knee sit-up only).One limitation to the hanging knee-up with strapsexercise is the occurrence of relatively high L4L5 diskcompression.2 However, L4L5 disk compression hasbeen shown to be slightly higher in the bent-knee sit-upexercise than in the hanging knee-up with straps exer-cise.2 Furthermore, in the present study, EMG valuesfrom the upper and lower rectus abdominis and internal

and external oblique muscles all were significantlyhigher in the hanging knee-up with straps exercise thanin the bent-knee sit-up exercise. Therefore, the hangingknee-up with straps exercise may be preferred over thebent-knee sit-up exercise for more fit individuals whowant to elicit a high-level challenge to the abdominalmusculature. Neither exercise, however, may be appro-priate for some people with low back pathologiesbecause of the relatively high L4L5 compression.

In general, all exercise variations of the Ab Revolution-izer device produced abdominal muscle activity similarto that produced by the crunch, bent-knee sit-up, andreverse crunch flat exercises. Therefore, purchasing thisabdominal device does not appear to offer any advan-tage in recruiting abdominal musculature over perform-ing traditional exercises that require no additionalequipment, such as the crunch, bent-knee sit-up, andreverse crunch flat exercises. However, one advantage ofthe Ab Revolutionizer device is that external weight canbe added, thereby allowing exercise intensity to bevaried. The reverse crunch flat and Ab Revolutionizerreverse crunch exercises were performed nearly identi-

Figure 8.Lower rectus abdominis muscle normalized electromyographic (EMG) activity (mean SD) among exercises. MVICmaximum voluntary isometriccontraction, degdegrees, Ab RevAb Revolutionizer, Wtsweights.



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cally, with the only difference being that the reversecrunch flat exercise was performed without the use of anabdominal device.

Biomechanical Differences Between Crunch andBent-Knee Sit-up ExercisesNot all abdominal exercises involve the same degree offlexion of the lumbar spine. Halpern and Bleck7 dem-onstrated that lumbar spinal flexion was only 3 degreesduring the crunch exercise but was approximately 30degrees during the bent-knee sit-up exercise. In addi-tion, the bent-knee sit-up exercise has been shown togenerate greater lumbar intradiskal pressure1,20 andcompression2 than have exercises similar to the crunchexercise, largely because of increased lumbar flexionand muscle activity from the rectus femoris and psoasmuscles.8,10 These findings suggest that the crunch exer-cise may be a safer exercise to perform than the bent-knee sit-up exercise for some people who need tominimize lumbar spinal flexion or compressive forcesbecause of lumbar pathologies.2

Although both the crunch and the bent-knee sit-upexercises were effective in recruiting abdominal muscu-lature, there were some differences. Several studies,including the present study, have shown that externaloblique muscle activity and, to a lesser extent, internaloblique muscle activity are significantly greater in thebent-knee sit-up exercise than in the crunch exer-cise.2,8,21,22 However, upper and lower rectus abdominismuscle activity have been shown to be greater in thecrunch exercise than in the bent-knee sit-up exercise.7,9

In addition, rectus femoris and psoas muscle activityhave been shown to be greater in the bent-knee sit-upexercise than in the crunch exercise,8,10 findings that areconsistent with the rectus femoris muscle EMG datafrom the present study. Increased muscle activity fromthe rectus femoris and psoas muscles may exacerbate lowback pain in some people with low back pathologies.

Abdominal and Oblique Muscle Recruitment in Crunchand Reverse Crunch ExercisesThere are beliefs that performing reverse crunch exer-cises activates the lower abdominal muscles to a greater

Figure 9.External oblique muscle normalized electromyographic (EMG) activity (mean SD) among exercises. MVICmaximum voluntary isometriccontraction, degdegrees, Ab RevAb Revolutionizer, Wtsweights.



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extent than does performing crunch exercises and thatperforming crunch exercises activates the upper abdom-inal muscles to a greater extent than does performingreverse crunch exercises, but the results from thepresent study do not substantiate these beliefs. In acomparison of the crunch and reverse crunch flat exer-cises, both upper and lower rectus abdominis muscleEMG activity were significantly greater during thecrunch, whereas the external and internal oblique mus-cle EMG activity were not significantly different betweenthe 2 exercises. Our data are similar to the findingsreported by Clark et al11 but different from the abdom-inal muscle EMG data reported by Willett et al,23 whofound greater lower rectus abdominis and externaloblique muscle activity with the reverse crunch exercisethan with the crunch exercise. These discrepancies mayhave been attributable to methodological differencesamong the studies. For example, in the study of Willettet al,23 the reverse crunch exercise was performed byhaving subjects raise the lower half of the body off thetable as far as possible, whereas in the present study,subjects were instructed to maximally posteriorly tilt thepelvis and flex the hips. However, significantly greaterupper rectus abdominis, internal oblique, and external

oblique muscle activity was seen when the reverse crunchinclined 30 degrees was performed rather than thecrunch exercise, but the lower rectus abdominis muscleactivity was not significantly different between the 2exercises.

Role of Abdominal Muscles in Trunk StabilityThe role of the abdominal muscles, especially the trans-verse abdominal and internal oblique muscles, inenhancing spinal and pelvic stabilization and increasingintra-abdominal pressure is well known.2428 Intra-abdominal pressure unloads the spine by generating atrunk extensor moment and tensile loading to the spineand reduces spinal axial compression and shear loads.29

The attachments of the transverse abdominal and inter-nal oblique muscles to the thoracolumbar fascia furtherenhance spinal and pelvic stabilization, because whenthese muscles contract, they tense the thoracolumbarfascia. The transverse abdominal muscle, which is thedeepest of the abdominal muscles, exhibits a muscleactivation pattern and an amplitude similar (within15%) to those of the internal oblique muscle duringmany of the same trunk flexion movements as those usedin the present study.8,18 The highest EMG activity from

Figure 10.Internal oblique muscle normalized electromyographic (EMG) activity (mean SD) among exercises. MVICmaximum voluntary isometriccontraction, degdegrees, Ab RevAb Revolutionizer, Wtsweights.



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the internal oblique muscle was obtained with the fol-lowing exercises: the Power Wheel roll-out, Power Wheelpike, Power Wheel knee-up, hanging knee-up withstraps, and reverse crunch inclined 30 degrees; thesedata suggest that these exercises also may offer moreeffective stabilization to the spine and pelvis than mayother exercises used in the present study, assuming that

transverse abdominal muscle activity is similar to internaloblique muscle activity during these exercises.

Exercise IntensityThe exercises used in the present study provide acontinuum of lower- to higher-intensity exercisesthrough which patients or clients can progress within atraining or rehabilitation program. Exercises involvingthe Ab Revolutionizer and abdominal crunch typicallywere easier for the subjects to perform than were exer-cises involving the hanging knee-ups with straps, PowerWheel pike and knee-up, and reverse crunch inclined 30degrees. However, because external weights could be

added to the Ab Revolutionizer, this exercise could beused to allow a person to progress from lower- tohigher-intensity exercises. The subjects participating inthe present study were all relatively young, active peoplewho were all able to perform both easier and moredifficult abdominal exercises. However, older, less active,or weaker people or people with trunk pathologies maynot be able to perform the more difficult exercises usedin the present study correctly. These higher-intensityexercises may be reserved for more fit patients andclients, such as athletes who are involved in rehabilita-tion and whose desire is to return to playing sports.

Extraneous (Nonabdominal) Muscle ActivityTo our knowledge, no studies have reported extraneousmuscle activity for any of the exercises used in thepresent study, except for the traditional crunch andbent-knee sit-up exercises, for which rectus femoris andpsoas muscle activity have been reported.8,10,18 To ourknowledge, no studies have reported latissimus dorsi orlumbar paraspinal muscle activity for any of the exercisesused in the present study. Interestingly, the Power Wheelroll-out, Power Wheel pike, Power Wheel knee-up, hang-ing knee-up with straps, and reverse crunch inclined 30

degrees exercises not only were the most effective exer-cises in activating abdominal musculature but also werethe most effective exercises in activating the latissimusdorsi muscle. However, all of these exercises, except forthe Power Wheel roll-out, also exhibited relatively highrectus femoris and lumbar paraspinal muscle activitycompared with the other exercises, a finding that may beproblematic for some people with low back pathologies.Therefore, the Power Wheel roll-out may be the mosteffective exercise in recruiting abdominal and latissimusdorsi musculature while minimizing rectus femoris andlumbar paraspinal muscle activity.

During the Power Wheel roll-out exercise, the latissimusdorsi muscle contracts eccentrically during the initialroll-out phase to control the rate of shoulder flexionattributable to gravity and concentrically in the returnphase as the shoulder extends. Although the rectusfemoris muscle appears to contract eccentrically duringthe initial roll-out phase (to control the rate of hip

extension) and concentrically during the return phaseto aid in hip flexion, we did not expect to find very lowrectus femoris muscle activity during the Power Wheelroll-out exercise. Although the psoas muscle EMG mag-nitudes were not measured in the present study becauseit is a deep muscle, it has been demonstrated that duringexercises performed in a position and manner similar tothose of the Power Wheel roll-out exercise, psoas muscleEMG magnitudes are low and typically are withinapproximately 10% of rectus femoris muscle EMG mag-nitudes.8,18 From these data, it can be hypothesized thatboth psoas and rectus femoris muscle activity is relativelylow during the Power Wheel roll-out exercise and that

the latissimus dorsi muscle may have a greater role thanthe rectus femoris and psoas muscles in controlling andcausing exercise movements during the Power Wheelroll-out exercise.

Because of the effectiveness of the Power Wheel roll-out,Power Wheel pike, Power Wheel knee-up, hangingknee-up with straps, and reverse crunch inclined 30degrees exercises in recruiting abdominal and extrane-ous musculature, these exercises may be beneficial forsome people who have limited workout time and whosegoal is to perform exercises that provide not only an

abdominal workout but also more of a total-body work-out. The greater relative intensity and number of mus-cles used during these exercises suggest that theseexercises also may achieve a greater energy expenditurethan may other exercises used in the present study.Moreover, tension in the latissimus dorsi muscle inaddition to the internal oblique muscle (and presumablythe transverse abdominal muscle), each of which tensesthe thoracolumbar fascia, may enhance trunk stabiliza-tion during these exercises.

Performing exercises that recruit the rectus femoris and

lumbar paraspinal muscles may not be advantageous forthose with weak abdominal muscles or lumbar instability,because the forces generated when these muscles con-tract act to anteriorly rotate the pelvis and increase thelordotic curve of the lumbar spine. Some people withweak abdominal muscles or lumbar instability may wantto avoid the bent-knee sit-up, Power Wheel pike, PowerWheel knee-up, and reverse crunch inclined 30 degreesexercises because of the relatively high rectus femorisand lumbar paraspinal muscle activity obtained withthese exercises compared with other exercises. In addi-tion, exercises performed in a manner similar to that of



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the aforementioned exercises exhibited psoas and ilia-cus muscle EMG magnitudes and recruitment patternssimilar to the EMG magnitudes and recruitment pat-terns of the rectus femoris muscle.18,21,22

These data suggest that the 3 primary hip flexorsthepsoas, iliacus, and rectus femoris musclesmay exhibit

similar EMG recruitment patterns and magnitudes whenthe exercises used in the present study are performed.The psoas muscle, through its attachments to the lumbarspine, attempts to hyperextend the spine as it helps flexthe hip, and this action may be detrimental to somepeople with lumbar instability. In addition, it has beendemonstrated that the psoas muscle can generate lum-bar compression and anterior shear force at L5S18,30;these effects may be problematic for some people withlumbar disk pathologies. Although muscle force fromthe lumbar paraspinal muscle also can increase thecompression of the lumbar spine, it should be noted thatall exercises used in the present study generated rela-

tively low muscle activity (10% of an MVIC) from thelumbar paraspinal muscle.

Effects of Electrode Placement on EMG Cross TalkThe electrode positions used in the present study havebeen shown to minimize EMG cross talk from othermuscles.15,17,19 This is especially true for the internaloblique muscle, the only muscle tested that was not asuperficial muscle. The internal oblique muscle nor-mally lies deep in relation to the external oblique muscleand therefore is susceptible to considerable EMG crosstalk from this muscle. However, it has been shown that

the internal oblique muscle is covered only by theaponeurosis of the external oblique muscle and not theexternal oblique muscle, within the triangle outlined bythe inguinal ligament, the lateral border of the rectussheath, and a line connecting the ASISs.19 Therefore,surface electrodes appear to be appropriate for use withthe internal oblique muscle when electrode placement iswithin this area, especially when clinical questions arebeing considered and when a small percentage of EMGcross talk is acceptable. It was shown that for trunkflexion exercises similar to the exercises performed inthe present study, mean internal and external oblique

muscle EMG data obtained from surface electrodes wereonly approximately 10% different from mean internaland external oblique EMG data obtained from intramus-cular electrodes.18 These authors demonstrated thatappropriately placed surface electrodes accuratelyreflect (within 10%) the muscle activity within theinternal or external oblique muscle.

Correlation Between EMG Amplitude and Muscle ForceLinear, quasi-linear (nearly linear), and nonlinear cor-relations have been reported for EMG amplitude andmuscle force (strength) in the literature.31,32 In general,

the relationship between EMG amplitude and muscleforce is most linear during isometric contractions orduring activities in which muscle length is not changingrapidly, which is what occurred with the exercises used inthe present study. In contrast, the relationship betweenEMG amplitude and muscle force is most nonlinearduring activities in which muscles change length rapidly

or during muscle fatigue. Therefore, the clinicianshould be cautious when relating EMG amplitude tomuscle force and strength during dynamic exercises.

ConclusionThe exercises used in the present study activated abdom-inal muscles by flexing the trunk (crunch and bent-kneesit-up), by flexing the hips with posterior pelvis rotation(Power Wheel pike, Power Wheel knee-up, hangingknee-up with straps, reverse crunch inclined 30 degrees,reverse crunch flat, Ab Revolutionizer reverse crunchwith weights, and Ab Revolutionizer reverse crunch), bya combination of flexing the trunk and flexing the hips

with posterior pelvis rotation (Ab Revolutionizer doublecrunch and Ab Revolutionizer oblique crunch), and byresisting trunk extension (Power Wheel roll-out). ThePower Wheel roll-out exercise was the most effectiveexercise in activating abdominal and latissimus dorsimuscles while minimizing lumbar paraspinal and rectusfemoris muscle activity. The Power Wheel roll-out, PowerWheel pike, Power Wheel knee-up, hanging knee-upwith straps, and reverse crunch inclined 30 degreesexercises were the most effective exercises in recruitingboth abdominal musculature and extraneous muscula-ture. Although both the bent-knee sit-up and the crunch

involved similar amounts of abdominal muscle activity,the crunch may be a safer exercise for people with lowback pathologies because of the relatively high rectusfemoris muscle activity. Moreover, the bent-knee sit-up,Power Wheel pike, Power Wheel knee-up, and reversecrunch inclined 30 degrees exercises may be problem-atic exercises for people with low back pathologiesbecause of the relatively high rectus femoris and lumbarparaspinal muscle activity.

References1Nachemson A. Lumbar intradiscal pressure. In: Jayson MIV, ed. TheLumbar Spine and Back Pain. Edinburgh, Scotland: Churchill Living-

stone; 1987:191203.

2Axler CT, McGill SM. Low back loads over a variety of abdominalexercises: searching for the safest abdominal challenge. Med Sci Sports

Exerc. 1997;29:804811.

3Ralston SH, Urquhart GD, Brzeski M, Sturrock RD. Prevalence ofvertebral compression fractures due to osteoporosis in ankylosingspondylitis.BMJ. 1990;300:563565.

4 Gardner-Morse MG, Stokes IA. The effects of abdominal musclecoactivation on lumbar spine stability. Spine. 1998;23:8691.

5Ricci B, Marchetti M, Figura F. Biomechanics of sit-up exercises. MedSci Sports Exerc. 1981;13:5459.



16/16

6Godfrey KE, Kindig LE, Windell EJ. Electromyographic study ofduration of muscle activity in sit-up variations. Arch Phys Med Rehabil.1977;58:132135.

7Halpern AA, Bleck EE. Sit-up exercises: an electromyographic study.Clin Orthop. 1979;145:172178.

8Juker D, McGill S, Kropf P, Steffen T. Quantitative intramuscularmyoelectric activity of lumbar portions of psoas and the abdominal wallduring a wide variety of tasks. Med Sci Sports Exerc. 1998;30:301310.

9Beim GM, Giraldo JL, Pincivero DM, et al. Abdominal strengtheningexercises: a comparative EMG study. Journal of Sport Rehabilitation.1997;6:1120.

10Guimaraes AC, Vaz MA, De Campos MI, Marantes R. The contri-bution of the rectus abdominis and rectus femoris in twelve selectedabdominal exercises: an electromyographic study. J Sports Med Phys

Fitness. 1991;31:222230.

11Clark KM, Holt LE, Sinyard J. Electromyographic comparison of theupper and lower rectus abdominis during abdominal exercises.

J Strength Cond Res. 2003;17:475483.

12 Demont RG, Lephart SM, Giraldo JL, et al. Comparison of twoabdominal training devices with an abdominal crunch using strengthand EMG measurements. J Sports Med Phys Fitness. 1999;39:253258.

13Sternlicht E, Rugg S. Electromyographic analysis of abdominalmuscle activity using portable abdominal exercise devices and atraditional crunch.J Strength Cond Res. 2003;17:463468.

14Warden SJ, Wajswelner H, Bennell KL. Comparison of Abshaperand conventionally performed abdominal exercises using surfaceelectromyography. Med Sci Sports Exerc. 1999;31:16561664.

15Balady GJ, Berra KA, Golding LA, et al.ACSMs Guidelines for ExerciseTesting and Prescription. Baltimore, Md: Lippincott Williams & Wilkins;2000:35312.

16Basmajian J, Blumenstein R. Electrode Placement in EMG Biofeedback.Baltimore, Md: Williams & Wilkins; 1980:7986.

17Cram J, Kasman G. Introduction to Surface Electromyography. Gaithers-

burg, Md: Aspen Publishers Inc; 1998:273374.

18McGill S, Juker D, Kropf P. Appropriately placed surface EMGelectrodes reflect deep muscle activity (psoas, quadratus lumborum,abdominal wall) in the lumbar spine. J Biomech. 1996;29:15031507.

19Ng JK, Kippers V, Richardson CA. Muscle fibre orientation ofabdominal muscles and suggested surface EMG electrode positions.

Electromyogr Clin Neurophysiol. 1998;38:5158.

20Nachemson AL. The lumbar spine: an orthopaedic challenge.Spine.1976;1:5971.

21Andersson EA, Ma Z, Thorstensson A. Relative EMG levels intraining exercises for abdominal and hip flexor muscles.Scand J RehabilMed. 1998;30:175183.

22Andersson EA, Nilsson J, Ma Z, Thorstensson A. Abdominal and hipflexor muscle activation during various training exercises. Eur J ApplPhysiol Occup Physiol. 1997;75:115123.

23Willett GM, Hyde JE, Uhrlaub MB, et al. Relative activity of abdom-inal muscles during commonly prescribed strengthening exercises.

J Strength Cond Res. 2001;15:480485.

24Thomson KD. Estimation of loads and stresses in abdominalmuscles during slow lifts. Proc Inst Mech Eng. 1997;211:271274.

25Richardson CA, Snijders CJ, Hides JA, et al. The relation betweenthe transversus abdominis muscles, sacroiliac joint mechanics, and lowback pain. Spine. 2002;27:399 405.

26Hodges PW, Richardson CA. Contraction of the abdominal muscles

associated with movement of the lower limb. Phys Ther. 1997;77:132142.

27Cresswell AG, Blake PL, Thorstensson A. The effect of an abdomi-nal muscle training program on intra-abdominal pressure. Scand JRehabil Med. 1994;26:7986.

28Cresswell AG, Grundstrom H, Thorstensson A. Observations onintra-abdominal pressure and patterns of abdominal intra-muscularactivity in man. Acta Physiol Scand. 1992;144:409 418.

29Daggfeldt K, Thorstensson A. The role of intra-abdominal pressurein spinal unloading. J Biomech. 1997;30:11491155.

30Santaguida PL, McGill SM. The psoas major muscle: a threedimensional geometric study. J Biomech. 1995;28:339345.

31Lippold OC. The relation between integrated action potentials in ahuman muscle and its isometric tension. J Physiol. 1952;117:492499.

32Lawrence JH, DeLuca CJ. Myoelectric signal versus force relation-ship in different human muscles. J Appl Physiol. 1983;54:16531659.

electromyographic analysis of traditional and non traditional abdominal exercises

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