vastus medialis oblique vastus lateralis muscle activity ratios

Vastus Medialis Oblique/Vastus Lateralis Muscle Activity Ratios for Selected Exercises in Persons With and Without Patellofemoral Pain Syndrome

Background and Purpose. The purpose of this study was to determine which of selected exercises with and without the feet free to move would enhance vastus medialis oblique muscle (VMO) activity over that of the vastus lateralis muscle (W) and whether the use of taping would increase VMO activity. Subjects. Twenty-one subjects without patellofemoral pain (PFP) syndrome and 10 subjects with PFP syndrome, aged 19 to 43 years @=26, SD= 71, participated. Metbods. Subjects were studied for the normalized, integrated electromyographic (IEMG) activity of their M O , W , and adductor magnus muscle (subjects without PFP syndrome) and the V M O m ratio using wire electrodes. Results. One exercise demonstrated greater activation of the VMO over the W when compared with similar exercises in subjects without PFP syndrome. The mean VMOhT activity ratio for terminal knee extension was 1.2 (SD= 0.5) with the hip medially rotated and 1.0 (SD= 0.4) with the hip laterally rotated. Al- though subjects reported that patellar taping decreased pain 94% during the step-down exercise, the V M O m ratio was not changed. Conclusion and Discussforr The results suggest that neither exercises purported to selectively activate VMO activity nor patellar taping improve the V M O m ratio over similar exercises. lCerny K. Vastus medialis oblique/vastus lateralis muscle activity ratios for selected exercises in persons with and without patellofemoral pain syndrome. Phys Ther. 1995; 75672- 683.1

Key Words: Adductor magnus, Electromyography, Patellc$moral, Vastus lateralis, Vastus medialis oblique.

Patellofemoral joint pain (PFP) is com- common site of knee pain in sports mon in the general population, occur- medicine clinics.'-5 Lateral malalign- ring more often in women and in ment of the patella has been sug- athletes, with the joint being the most gested as one of the major causes of

K Cerny, PhD, PT, is Professor, Department of Physical Therapy, College of Health and Human Services, California State University, Long Beach, Long Beach, CA 90840-5603 (USA) ([email protected]).

The study protocol was approved by the Human Subjects Committee, California State University, Long Beach.

Results of this research were previously presented at the 1991 and 1992 Annual Conferences of the California Chapter of the American Physical Therapy Association and at the 1991 and 1922 Annual Conferences of the Long Beach Veterans Administration Hospital-California State Univer- sity, Long Beach-Memorial Medical Center of Long Beach.

m k article was submitted August 24, 1994, and was accepted April 3, 1995.

--

Kay Cemy

PFP syndrome.4-6-8 As a result, both surgical and conservative treatments to correct this rnalalignrnent have been suggested.1~4-10

Many exercise treatments emphasize the importance of the vastus medialis oblique muscle (VM0)6,8,10 because of its medial pull on the patella.11-15 Some researcherslb-19 suggest that contraction of the hip adductor and quadriceps femoris muscles simulta- neously would preferentially activate the VMO. Other researchersl7.19 report that the vastus medialis muscle (VM) is activated preferentially in response to

26 / 672 Physical Therapy / Volume 75, Number 8 / August 1995

Table 1, Subject Anthmpometric Data

NO. of Age - 0 - Body Weight (Ibb)

Subjects X SD Range X SD Range

Subjects without PFPB syndrome

Women 10

Men 11

Subjects with PFP syndrome

Women

Men

"PFP=patellofemoral pain.

bl lb=0.4536 kg.

valgus stress at the knee caused by hip lateral rotation during knee extension exercises and that hip medial rotation, therefore, decreases the activity of the VM. Still others9'20921 have reported greater VMO activity during knee extension with the knee rela- tively flex.ed than in terminal knee extension. Knee extension exercise with tibia'l medial rotation has been proposed because the VMO is purported to prevent lateral rotation of the tibial8.19 and therefore to decrease the quadriceps femoris muscle angle (Q angle) and lateral patellar tracking.22 Pronation of the subtalar joint and medial rotation of the tibia, however, have also been claimed to increase lateral tracki11g.~,~3

McConnel16J6 trains patients with PFP syndrome in unilateral and bilateral limb flexion exercises in weight bear- ing (walk stance and wall slide) and stepdown exercises because these patients have increased pain with these activities. Although soft bracing has previously been suggested to negate the valgus force of the quadriceps femoris muscles on the patella,l,5 McConnel16J6 suggests improving patellar tracking, decreasing pain, and increasing the vastus medialis oblique/ vastus lateralis muscle (VMO/VL) activity ratio in persons with PlT by taping the patella or tensor fascia lata muscle medially. Little evidence exists to support the use of the exercises and procedures reviewed.

The primary purpose of this study was to determine whether any of the exercises purported to increase the activity of the VMO over the VL, the VMO/VL activity ratio, did so when compared with similar exercises in subjects with and without PlT. A secondary purpose of this investigation was to determine whether therapeutic medial-glide taping altered the activity of the VMO or the VL or the VMO/VL activity ratio. Another purpose was to determine which of similar exercises increased the activity of the VMO, VL, and adductor magnus muscle (AM). Finally, I wanted to determine whether gender influenced the muscle activity studied.

Method

Subjects

Twenty-one subjects who had no known lower-limb musculoskeletal impairments and who exhibited no signs of neurological impairment and 10 subjects with PlT participated in this study. The subjects' average age, average body weight, and gender are shown in Table 1. Subjects with syrnp- toms had a physician's diagnosis of PFP within 6 years of the testing date and reported retropatellar pain during at least two of the following activities: (1) squatting, (2) ascending and de- scending stairs, and (3) prolonged sitting.1-3s4 All subjects with PlT performed a step-down exercise from a 22.9-cm (9-in) stool with and without medial-glide taping of the patella be-

fore beginning the study. The subjects rated their pain after stepdown exercise on a scale of 1 to 10, with 1 being minimal pain and 10 being the worst pain that they could imagine, and they reported the percentage of change in pain with step down after taping. The subjects with PlT were required to have at least a 50% reduction in pain with patellar taping to participate in the study. All subjects provided in- formed consent consistent with university policy.

Myoelectric activity was measured by use of indwelling wire electrodes of 50-pm nickel alloy. The electrodes, insulated except for 2 rnrn at the ends, were inserted into the muscle with a 25-gauge needle. The needle was withdrawn, leaving the barbed ends of the wire electrodes in place. The wire electrodes were inserted into the VMO and VL of all subjects. In addition, a wire electrode was placed in the AM of the subjects without PlT syndrome to ensure that they were contracting the muscle during exercises. The wire for the VMO was placed in the middle of the muscle belly. The wire for the VL was placed in the muscle approximately one third of the distance from the patella to the anterior superior iliac spine. The wire for the AM was inserted into the muscle just anterior to the gracilis muscle, approximately one third of the distance from the medial femoral epicondyle to the syrnphysis

Physical 'Therapy / Volume 75, Number 8 / August 1995 673 / 27

pubis. The locations of the VL and AM inseltions were chosen because they proved to be the most distal locations, consistently affording a full electromyographic (EMG) interference pattern upon muscle activation during pilot testing. The distal VL insertion was used to sample the oblique por- tion of the VL, which is purported to best oppose the action of the VM0.12 The distal AM insertion was used to sample its activity near the origin of the VMO.'3 The leg each subject said was the dominant leg was tested in all except one of the subjects without PFP syndrome. The nondorninant limb was tested in one subject without PFP syndrome because he had a previous knee surgery on the dominant side. The most severely involved leg of the subjects with PFP was tested.

In order to decrease the chance of wire electrode migration during testing, subjects contracted the inserted muscle maximally several times after needle insertion to pull the wire into the muscle. In addition, the investigator moved the limb into full knee flexion and extension and full hip abduction and adduction to allow the wire to slip further into the tissues before taping the external wire to the limb with a stress-relief loop.

Surface ground plates and the telemetry system were attached to the subject, and the electrode wires were connected to attachment posts on the ground plates. Myoelectric signals were differentially amplified, band- pass filtered (50-850 Hz), and trans- mitted by FM-FM telemetry to a re- ceiver interfaced to a B&L computer (model 286): Placement of electrodes in the vastus muscles rather than rec- tus femoris muscle was confirmed by noting activity during isometric knee extension and silence during combined isometric hip and knee flexion. Placement in the AM rather than the VM was confirmed by noting activity during isometric hip adduction and silence during isometric knee extension. The EMG activity was then re-

'B&L Engineering, 12309 E Florence Ave, Santa

corded during rest and during maximal manual resistance tests. All recordings during the resistance tests were obtained with the subjects positioned supine and supported on their elbows. For the VMO and VL tests, the subjects' knee extension was resisted while the hip and knee were flexed approximately 30 degrees. For the AM test, the subjects were resisted for hip adduction with the knee extended.

Exercise Pmcedures

Exercises included what Lehmkuhl and Smith24 and Soderberg25 have described as "open-chain and "closed-chain" activities of the lower limb, performed in random order for 5 seconds each. Lower-limb open-chain exercises were performed with the sole of the foot free to move, whereas closed-chain exercises had the sole of the foot planted on the floor. The terms "open chain and "closed chain" are used here to denote whether the distal limb segment was free to move when the quadriceps femoris muscles contracted. Open-chain exercises were randomly chosen to be performed prior to or after closed-chain exercises. Subjects practiced dynamic exercises until the investigators were satisfied that movements were smoothly timed with a metronome at 1 beat per second. Starting positions of the knee were monitored with a standard goni- ometer. Subjects moved and their EMG activity was recorded during exercises, beginning on the beat of a metronome. Movement began with a "go" command from the investigator immediately following a "ready" command at the previous metronome beat. Electromyographic recording during isometric exercises began after the raw EMG level stabilized in a full interference pattern. In consideration of the tolerance of the subjects with PFP syndrome, fewer exercises were performed by the subjects with PFP syndrome than by the subjects without PFP syndrome. Abbreviations and definitions of the exercises used in this study are presented in Table 2.

Fe Springs, CA 90670

Exercises for Subjects Without PFP Syndrome: Open Chain

Three groups of open-chain activities were used for interexercise comparison: quadriceps femoris muscle setting ("quad sets"), knee extension, and isometric holds. All exercises were performed against the resistance of an ankle cuff weight equal to 5% of each subject's body weight to the nearest pound.

Quad sets (QS). Quad sets were isometric exercises performed in full knee extension with the subjects positioned long sitting and supported on their hands with their heels lifted off of the table to decrease the possibility of substitution by hip extensor activity. The six quad set exercises were done with (1) the hip and ankle positioned in neutral (QS), (2) the hip maximally medially rotated and the ankle positioned in neutral (QSMR), (3) the hip maximally laterally rotated and the ankle positioned in neutral (QSLR), (4) the hip maximally adducted against a pillow bolster with the ankle positioned in neutral (QSA), (5) the hip positioned in neutral and the ankle maximally dorsiflexed (QSDF), and (6) the hip positioned in neutral and the ankle maximally plantar flexed (QSPF).

Knee extension (KE). The knee extension exercises were performed with the subjects in a sitting position with the knee flexed from 30 to 0 degrees and the ankle positioned in neutral. The movement was timed with a metronome for 3 seconds, followed by a 2-second hold at full extension. The three exercises were performed with (1) the hip positioned in neutral (ICE), (2) the hip maximally laterally rotated (KELR), and (3) the hip maximally medially rotated (KEMR).

Isometric holds in flexion (IS). Iso- metric hold exercises were isometric knee extension exercises performed with the subjects in a sitting position with their hip and ankle positioned in neutral. The five exercises were done with (1) the knee flexed 15 degrees and the tibia in neutral rotation (IS15),

Physical Therapy / Volume 75, Number 8 / August 1995

Table 2. Exercise Abbreviations and Dejinitions

Abbreviation Definition

Exercises for subjects without patellofemoral joint pain syndrome

Open chain

Quadriceps femoris muscle set (QS)

QS

QSML

lsornetric at full knee extension

Hip and ankle neutral

Hip maximally medially rotated, ankle neutral

QSLR Hip maximally laterally rotated, ankle neutral

QS A

QSDF

QSPF

Knee extension (KE)

KE

KEMR

KELH

Isometric hold (IS)

IS1 5

IS45

IS60

IS45MR

IS45LR

Closed chain

Walk stance-step down (WS-SD)

WSS

WSP

WSPT

WSTT

SD

Wall slide (WSI)

WSI

WSIA

Exercises for subjects with patellofemoral joint pain syndrome

Open chain

QS, 1515, IS601, KE

Closed chain

WS, WSI, WSIA, SD

Hip adducting against a bolster, ankle neutral

Hip neutral, ankle maximalty dorsiflexed

Hip neutral, ankle maximally plantar flexed

30" to 0" extension, ankle neutral

Hip neutral

Hip maximally medially rotated

Hip maximally laterally rotated

Hip and ankle neutral

Knee at 15" flexion, tibia in neutral rotation



Knee at 45" flexion, tibia maximally medially rotated

Knee at 45" flexion, tibia maximally laterally rotated

Unilateral knee flexion to 45", hip in neutral rotation and subtalar joint unconstrained

WS with subtalar joint in maximal supination

WS with subtalar joint in maximal pronation

WS after patellar medial-glide taping

WS after medial-glide taping of the tensor fascia lata muscle

Step down from a 22.9-cm (9-in) stool leading with contralateral limb, hip in neutral rotation and subtalar joint unconstrained

Bilateral knee flexion to 45", hip in neutral rotation

WSI while hip adducting against bolster

As described above

As described above

Isometric knee extension and hip adduction against a bolster sitting with sole of foot on floor

(2) the knee flexed 60 degrees and the Exercises for Subjects Without seconds, followed by a 2-second hold tibia in neutral rotation (IS60), (3) the PFP Syndmme: Closed Chain at the end position. knee flexed 45 degrees and the tibia in neutral rotation (IS45), (4) the knee Two groups of closed-chain exercises Walk stance-step down (WS-SO). flexed 45 degrees and the tibia maxi- were used for interexercise compari- Walk-stance exercises were unilateral rnally laterally rotated (IS45LR), and son: (1) walk-stance and step-down exercises performed to 45 degrees of (5) the knee flexed 45 degrees and the exercises and (2) wall-slide exercises. knee flexion with the hip in neutral tibia maximally medially rotated Movements were performed for 3 rotation and the subject's weight sup- (IS45MR)

Physical Therapy /Volume 75, Number 8 /August 1995

ported on the forward, tested limb. The opposite toe was permitted to remain on the floor for balance only. Balance was also provided by touch- ing the hands of an investigator. The five exercises were performed with (1) the subtalar joint unconstrained (WS); (2) the subtalar joint maximally supinated (WSS); (3) subtalar joint maximally pronated (WSP); (4) the subtalar joint unconstrained after the patella was taped medially with a media frontal-plane tilt and rotation to position the inferior pole of the patella inferiorly (WSPT); and (5) the subtalar joint unconstrained after tensor fascia lata muscle medial-glide taping (WSrr3.

The final exercise was a step down from a 22.9-cm stool, with the subject leading with the contralateral limb while the tested limb was in neutral hip rotation. The hold was with the contralateral foot just off of the floor (SD).

Wall slide (WSO. The wall-slide exercises were bilateral exercises that the subjects performed from an upright standing position to 45 degrees of knee flexion while the trunk main- tained contact with the wall. This was done to prevent decreasing the quadriceps femoris muscle demand by shlftig the center of gravity of the trunk anteriorly. The subjects' feet were parallel, shoulder width apart, and just far enough from the wall to allow knee flexion to 45 degrees. The hips were in neutral rotation. The two wall-slide exercises were performed as (1) a straight wall slide (WSl) and (2) a wall slide while squeezing a pillow bolster between the knees (WSlA).

Exercises for Subjects With PFP Syndmme

exercises with and without patellar taping.

Open-chain exercises were QS, IS15, IS60, and KE. Closed-chain exercises were done both before and after the patella was taped medially with a medial frontal-plane tilt and rotation to position the inferior pole of the patella inferiorly. The closed-chain exercises were WS, WSl, WSlA, SD, and isometric knee extension and hip adduction in a sitting position with hips and knees flexed to 90 degrees (ISQA). This exercise was considered closed chain because subjects were instructed to contract the vastus muscles by pushing the foot against the floor and to squeeze the bolster maximally.

At the end of testing, wire electrodes were slipped out of the muscle, and the skin was cleaned with alcohol. Total testing time was 1Y2 to 2 hours per subject.

Data Anahsis

The EMG activity was digitized at 2,000 samples per second through an AID convertert run by the B&L software (version 4.19).* The software then rectified the signals and set noise thresholds from the first 2 seconds of activity of the resting EMG record. The threshold was the lowest level of activity recorded below which 95% of the resting EMG signal was found. Only EMG activity greater than threshold was then quantified by integration. Signals were integrated each 1/50 second for each 5-second exercise. The EMG values for each exercise were normalized by the software by division by the EMG value from the maximal exercise tests. All EMG values reported are therefore expressed as a percentage of maximal activity.

Procedures were identical to those for Within-day reliability of the integrated, subjects without PFP syndrome, unless normalized EMG values for the VMO, otherwise noted. Groups of exercises the VL, and the VMOnZ ratio was for interexercise comparison were previously established in 12 subjects open-chain exercises and closed-chain without PFP syndrome by intraclass

tModel DT2801-A, Data Translation, 100 Locke Dr, Marlborough, MA 01752-1192.

QMDP Statistical Software Inc, Los Angeles, CA 90086

correlation coefficients (ICC[3,1D for two repeated measures of QS, QSA, IS60, IS15, WS, WSl, WSlA, SD, and knee extension from 30 to 0 degrees of flexion using the same EMG pro- cessing as in this study. Two insertion sites in locations bordering within 1.27 cm (0.5 in) of those used in thls study were sampled for each muscle. Eighty percent of all ICCs were above .30. Reliability averaged .81 for the VMO, ranging from .37 to .98, and averaged .91 for the VL, ranging from .77 to .98. The VMO/VL ratio averaged .93, ranging from .88 to .%, with the exception of .55 for walk stance using the lower insertion sites. The walk-stance ratio for the upper insertion sites was .97.

The average EMG value was calculated for each muscle of each subject for each exercise, and a VMO/VL ratio was calculated from these values. Mean values for VMO, VL, and AM myoelectric activity and the VMO/VL ratio were calculated for each exercise. Exercises in each of the five groups of exercises for subjects without PFP syndrome (QS, KE, IS, WS-SD, WSl) were compared across exercises for muscle activity and VMO/VL ratio by a two-way repeated-measures multivari- ate analysis of variance (MANOVA), with gender as the grouping factor. Exercises for openchain activities for patients with PFP syndrome were compared across exercises for muscle activity and VMOm ratio by a one- way repeated-measures MANOVA. Exercises for closed-chain activities for subjects with PFP were compared across exercises for muscle activity and VMONL ratio by a two-way repeated-measures MANOVA, with taping as the grouping factor. When MANOVA results were sigdicant, a subsequent univariate analysis of variance (ANOVA) was done for each muscle tested. A level of significance of .05 was accepted, and a Bonferroni adjustment was used for post hoc t tests. The BMDP statistical was used for all analyses.

AU reported significant results refer to post hoc sigmlicance. For these results,

30 / 676 Physical Therapy / Volume 75, Number 8 / August 1995

Table 3. Integrated Electromyograpbic Activity (Percentage ofMaximum) During Quadriceps Femoris Musclea Set of Exercises for Subjects Without Patellofemoral Pain Syndrome (N=20)

VMO VL AM VMONL

X SD Minimum Maximum X SD Minimum Maximum x SD Minimum Maximum X SD Minimum Maximum

Neutral 53 26 13 97 50 23 6 80 12 22b 0 68 1.2 0.5 0.6 3.0

Hip medial rotation 53 28 10 11 1 46 22 7 79 16 25 0 78 1.2 0.5 0.4 2.9

Hip latetal rotation 48 27 9 91 48 24 3 87 7 10 0 31 1.1 0.6 0.2 3.5

Hip adduction 56 23 2 94 52 19 20 86 32 206 1 75 1.1 0.4 0.0 2.1

Ankle dorsiflexion 58 24 7 92 52 21 10 92 14 25 0 78 1.2 0.4 0.2 2.0

Ankle plantar flexion 52 24 7 84 50 27 5 105 5 11 0 45 1.2 0.5 0.6 2.8

"Muscle ahbreviations: vastus medialis oblique (VMO), vastus lateralis (VL), adductor magnus (AM)

b~ignificant post hoc difference for two-way analysis of variance (F= 11.7; df= 1,8; P=.0031).

the MANOVA and ANOVA results were also significant.

Subjects Without PFP Syndrome

Due to rc:cording difficulties, one male subject's data were lost for the quad set and closed-chain exercises.

Open-chain exemises. Means and standard deviations of data and comparisons that yielded statistically significant results are reported in Tables 3 through 5. No differences in myoelectric activity due to gender were seen. Comparison of the quad set exercise with all its variants showed no differences due to ankle or hip rotation

position for the VMO, VL, or VMOM ratio (Tab. 3). The EMG activity ranged from 48% to 58% of maximum for the VMO and from 46% to 52% of maximum for the VL. The VMO/VL ratio ranged from 1.1 to 1.2. Although AM activity was higher for QSA (32%2200/0) than for QS (12%222%), the increased AM activity did not affect the VMO, VL, or VMO/VL ratio activity (Tab. 3).

Knee extension exercises were compared post hoc between KE and both KEMR and KELR and between KEMR and KELR. Comparisons of KE with KEMR and KELR showed higher VMO and VL activity in the KE exercise

(34%+ 18% and 35%+ 15%, respectively) than in either rotated position of the hlp. The VMO activity was 28%+6% for KEMR and 22%+12% for KELR, whereas VL activity was 28%2 13% for KEMR and 26%+ 12% for KELR (Tab. 4). No difference, however, was seen in the VMO/VL ratio between KE and either KEMR or KELR. Comparison between KEMR and KELR showed higher VMO activity and VMO/VL activity ratio in KEMR than in KELR (Tab. 4). The VMO/VL ratio was 1.2 20.5 for KEMR and 1.020.4 for KELR.

Isometric hold exercises were compared post hoc between IS60 and both -

Table 4. Integrated Electromyograpbic Activity (Percentage of Maximum) During Knee Extension Exercises From 30 to 0 Degrees for Subjects Without Patellofemoral Pain Syndrome (N= 21)"

VMO VL AM VMONL

2 SD Minimum Maximum X SD Minimum Maximum X SD Minimum Maximum X SD Minimum Maximum

- -

HIP neutral 34 18b.c 3 81 35 15d,e 14 64 4 8 0 36 1.1 0.4 0.6 2.0

HIP medial rotation 28 1 6b 8 84 28 13d 7 54 3 8 0 37 1.2 0.5' 0.5 2.4

Hip lateral rotat~on 22 12' 4 64 26 12e 10 5 1 8 26 0 116 1 .O 0.4' 0.3 2.2

-- --

"Muscle abbreviations: vastus medialis oblique (VMO), vastus lateralis (VL), adductor magnus (AM).

b~ignificanr post hoc difference for two-way analysis of variance (ANOVA) (F= 10.2; df= 1,19; P=.0049.)

'Significanl. post hoc difference for two-way ANOVA (F=21.1; df= 1,19; F .0002) .

d~ignilicant post hoc difference for two-way ANOVA ( F 1 7 . 3 ; df= 1,19; F ,0005).

eSignilicanf post hoc difference for two-way ANOVA (F=13.4; dp1,19; P=.0017).

'Significant past hoc daerence for two-way ANOVA (F=10.0; df=1,19; F .0049) .

Physical Therapy / Volume 75, Number 8 /August 1995

- Table 6. Integrated Electromyographic Activfty (Percentage of Mam'mum) During Zsometrlc Exercise for Subjects Without Patellofemoral Pain Syndrome (N=21,P

VMO VL AM VMONL

2 SD Minimum Maximum X SD Minimum Maximum X SD Minimum Maximum x SD Minimum Maximum

Knee flexion posture

60" 5 3b 1 14 5 3C 1 12 1 2 0 6 1.3 1.2 0.1 5.0

45" 5 4 0 17 7 6 0 18 1 3 0 12 1.3 1.3 0.2 4.4

Tibial medial rotation 6 4 0 15 8 5 2 17 1 2 0 10 1.2 1.4 0.2 4.8

Tibial lateral rotation 5 4 0 17 8 6 1 20 1 2 0 10 1.0 1.0 0.1 3.6

15" 18 1 2 ~ 0 61 22 10C 8 42 3 4 0 15 1.0 0.5 0.3 2.5

"Muscle abbreviations: vastus medialis oblique (VMO), vastus lateralis (VL), adductor magnus (AM).

*significant post hoc difference for two-way analysis of variance (ANOVA) (F=34.9; df--1,19; P=.0000).

'Significant post hoc di5erence for two-way ANOVA (F=84.7; dp1,19; P=.0000)

IS15 and IS45 and between IS45 and both IS45MR and IS45LR. Less myoelectric activity of the VMO and VL was seen in IS60 (5%+3% for both) than in IS15 (18%+12% and 22%+ I@?, respectively) without a change in the VMO/VL ratio (Tab. 5). Tibial rotation did not affect the VMO or VL activity or the VMO/VL ratio for the 45-degree position.

Closed-chain exemises. Data were lost while recording the activity during the WSFT in 1 male subject. Analysis was therefore performed on 19 subjects for all six exercises in the WS-SD group and also for all 20 subjects for the remaining five exercises. No differences resulted between these analyses.

Means and standard deviations of data and comparisons that yielded statistically significant results are reported in Tables 6 and 7. Gender/exercise inter- actions were seen for the VMO and VL for the WS-SD exercise group. Athough muscle activity was similar between men and women for all WS exercises, ranging from 11% to 15% for women and from 11% to 16% for men, women required approximately twice the activity as men for SD (Tab. 6). Average VMO activity was 24%211% for men and 45%+60/0 for women, whereas VL activity averaged 19??7% for men and 41%+3% for women.

Separate analysis by gender for the VMO and VL comparing WS with WSS, WSP, WSFT, WS'IT, and SD tended to show greater activity for both the VMO and VL during the SD exercise than during the WS exercise (Tab. 6). Both muscle values for women but only VL values for men were different between SD and WS. When data from men and women were combined, the difference in VMO activity between SD and WS was sigmlicant (P=.0000). No influence of gender or exercise was seen for either AM activity or VMO/VL ratio for the WS-SD exercise comparisons, although a trend toward increased AM activity from WS to SD was found.

No differences in EMG activity due to gender were seen in WSl exercises. Likewise, no difference in VMO/VL ratio was seen between WSl and WSh, but greater activity was seen in the AM, VMO, and VL during WSlA than in WS1 (Tab. 7). The AM activity increased from 2%+ 3% to 30%+ 53% when adduction was added to the WS1 exercise. The VMO increased from 9?+6% to 17%+7%, whereas the VL increased from 9?+5% to 17%+8% with the addition of adduction to WSl.

Subjects With PFP Syndrome

Means and standard deviations of data and comparisons that yielded statisti-

cally sigmlicant results for open- and closed-chain exercises are given in Tables 8 and 9, respectively. The VMOM. ratio did not d&er in comparisons of QS with IS60, IS15, and KE and of IS60 with IS15 (Tab. 8). Higher VMO and VL activity, however, occurred during the QS activity than in any other open-chain activity. The QS activity was 101%+30% for the VMO and 90?!+36% for the VL. The highest activity in other open-chain exercises was 49/02 17% for the VMO and 48%+ 17% for the VL during KE. In addition, IS15 demanded more vastus muscle activity than did IS60 (Tab. 8). The VMO activity increased from 6%+ 5% for IS60 to 40%+ 25% for IS15, whereas VL activity increased from 7%+6% to 37%+21%, respectively.

Patellar taping did not affect closed- chain muscle activity, even though the decrease in pain after patellar taping for the SD exercise averaged 94%. Analyses comparing WS with WSl, SD, and ISQA and WSl with WSlA were not sigdicant for the VMOM ratio (Tab. 9). Both the VMO and VL were less active in the WS (31%+ 23 for VMO and 38%+36% for VL.) than in the SD (65%?22% for VMO and 77%+36% for VL) or ISQA (63%+31% for VMO and 69/0+36% for VL). The VMO increased its activity when adduction was added to the wall slide from 13%+7% to 30%+ 18%. The

32 / 678 Physical Therapy /Volume 75, Number 8 /August 1995

Table 6. Integrated Electromyographic Activity (Percentage ofMaximum) During Walk-Stance and Step-Down Exercbes for Subjects Without Patellofemoral Pain Syndrome (N= 207

VMO VL AM V M O M - X SD Minimum Maximum X SD Minimum Maximum X SD Minimum Maximum X SD Minimum Maximum

Walk-stance neutral 11 24b 0 105 1.3 0.2 0.4 4.9

Women 12 8' 2 27 11 5d 2 20

Men 13 6e 5 22 13 9' 3 30

Walk-stance supinated 9 10 0 55 1.1 0.4 0.5 2.6

Women 15 9 6 29 14 6 7 23

Men 14 6 5 28 15 7 5 32

Walk-stance pronated 5 7 0 26 1.0 0.4 0.4 2.1

Women 14 9 3 37 15 8 4 32

Men 15 6 8 26 16 6 5 23

Walk-stance TFLg tape 7 13 0 56 1.1 0.5 0.5 2.3

Women 14 7 8 26 13 4 7 20

Men 13 6 3 23 13 8 4 28

Walk-stance patellar tape (n = 19) 9 15 0 59 1.3 0.9 0.5 4.1

Women(n=lO) 12 6 2 2 1 11 6 3 22

Men (n=9) 13 6 4 25 11 8 5 31

Step down 21 2d) 0 7 1 1.2 0.6 0.5 3.4

Women 45 6' 35 54 41 13d 23 69

Men 2 4 1 1 7 40e 19 7' 10 32

aMuscle abbreviations: vastus medialis oblique (VMO), vastus lateralis (VL), adductor rnagnus (AM).

rend for past hoc difference for two-way analysis of variance (ANOVA) not significant ( P 3 . 9 ; df-1,18; P=.0630).

"Significant post hoc difference for one-way ANOVA (F=154.4; df-1,9; P=.0000).

d~ignificant post hoc dierence for one-way ANOVA (F=61.6; df-1,9; P=.0000).

'Trend for post hoc difference for one-way ANOVA not significant (F=10.3; df-1,9; P=.0106), Note: P=.0000 when men and women combined (F=102.9; df-1,181.

/Significant post hoc difference for one-way ANOVA (F 11.8; df- 1,9; F ,0074).

Tensor fascia lata muscle.

Table 7. Integrated Electtomyographic Activity (Percentage of Mm'mum) During Wall-Slide Exercbes With and Without Hip Adduction for Subjects Without Patellofemoral Pain Syndrome (N=207

VMO VL AM VMONL - X SD Minimum Maximum % SD Minimum Maximum X SD Minimum Maximum x SD Minimum Maximum

Without adduction 9 6b 1 18 9 5' 1 18 2 3d 0 12 1.3 1.2 0.3 5.3

With adduction 17 7b 6 32 17 8' 5 31 30 53d 1 240 1.2 0.7 0.4 3.1

aMuscle abbreviations: vastus medialis oblique WMO), vastus lateralis (VL), adductor magnus (AM)

b~ignificant difference for two-way analysis of variance (ANOVA) (F=28.3; df-1,18; P=.0000).

'Significant difference for two-way ANOVA (F=35.5; df-1,18; P=.0000).

d~ignificant difference for two-way ANOVA (F=6.0; df-1,18; e . 0 2 5 3 )

Physical Therapy / Volume 75, Number 8 /August 1995

increase in the VL activity from Discussion effectively compare the EMG signal 16%? 10% for WSI to 36%?32% with between muscles, each of which may WSlA did not reach the rigor of post Technique be a different distance from the re- ha: significance. cording electrode, and between sub-

The amount of EMG signal recorded is jects, each of whom may have dependent on the location and size of different-sized muscles and different the recording electrodes. In order to distances from active muscle to elec- -

Table 8. Integrated Electromyographic Activity (Percentage of Maximum1 During Open-Chain Exercises for Subjects With Patellofemoral Pain Syndrome (N= 10)"

VMO VL VMONL - - X SD Minimum Maximum X SD Minimum Maximum X SD Minimum Maximum

Quadriceps femoris muscle set 101 3 P d 54 149 90 36e-g 42 149 1.2 0.5 0.8 2.3

Isometric at 60' 6 5b*h 1 14 7 6e,i 2 22 1.0 1.0 0.0 3.3

Isometric at 15" 40 25C,h 12 81 37 21f,j 6 73 1.2 0.6 0.3 2.4

Extension 30"-0" 49 17d 31 79 48 17g 27 67 1.1 0.4 0.5 2.2

"Muscle abbreviations: vastus medialis oblique (VMO), vastus lateralis (VL). Note: extension was not compared with isometric exercises.

b~ignificant post hoc difference for analysis of variance (ANOVA) (F= 103.4; df= 1 9 ; P= ,0000).

'Significant post hoc difference for ANOVA (F=60.1; df= 1,9; F.0000) .

d~ignificant post hoc difference for ANOVA (F=41.4; df= 1 ,9 ; P= ,0001).

'Significant post hoc difference for ANOVA (F= 52.2; df= 1,9; P= .0000).

/significant post hoc difference for ANOVA (F=29.0; d p 1,9; P=.0004).

RSignificant post hoc difference for ANOVA (F=21.1; d p 1 , 9 ; P= ,0013).

'significant post hoc difference for ANOVA (F=25.6; df= 1,9; e . 0 0 0 7 ) .

'Significant post hoc ditference for ANOVA (F=24.4; df-1,9; F .0008) . - Table 9. Integrated Electromyographic Activity (Percentage of Mmammum) During Closed-Chain Exercises for Subjects With Patellofernoral Pain Syndrome (N= 101"

VMO VL VMONL - X SD Minimum Maximum X SD Minimum Maximum x SD Minimum Maximum

Walk stance 31 23beC 6 89 38 36d,e 8 137 1 .O 0.6 0.3 2.6

Wall slide 13 7' 2 28 16 109 5 45 0.9 0.5 0.3 2.0

Wall slide with adduction 30 18' 8 74 36 32g 11 131 1.0 0.5 0.3 2.0

Step down 65 22b 31 98 77 36d 40 171 0.9 0.3 0.5 1.4

Isometric sitting at 90' with adduction 63 31" 13 148 69 36e 27 173 1.0 0.4 0.4 1.9

"Muscle abbreviations: vastus medialis oblique (VMO), vastus lateralis 0.2). Data averaged for patellar taped and untaped exercises

b~ignificant post hoc difference for two-way analysis of variance (ANOVA) (F=50.9; df= 1,9; P=.0001).

'Significant post hoc ditference for two-way ANOVA (F=18.5; df=1,9; P=.0020).

d~ignificant post hoc diference for two-way ANOVA (F=218.3; d p 1 , 9 ; P=0000).

'Significant post hoc difference for two-way ANOVA (F=56.3; df=1,9; P=0000).

&&cant post hoc d8erence for two-way ANOVA (F= 11.1; df= 1,9; P= ,0088).

8Trend for past hoc difference for two-way ANOVA (F=6.3; df=1,9; e . 0 3 3 6 ) .


trodes, a method of expressing the EMG activity of a spechc muscle as a ratio of activity to some reference value eliminates the influence of location and size of recording electrodes. Use of the maximum isometric EMG activity as the normalizing factor al- lows expression of activity in an easily understandable ratio and has been shown to provide better reliability (ICC) than using either dynamic maximal or submaximal EMG activity in the gastrocnemius muscle.26

The software used for data collection prevented collection of data for less than 5 seconds per trial. Because movement during dynamic exercise would be much slower than custom- ary in clinical practice if movement was prolonged for 5 seconds, only 3 seconds of movement was used, with a 2-second hold at the end position. As a result, two fifths of each dynamic exercise was actually isometric. Be- cause no differences were found in VMO/VL ratios at different isometric positions, this practice of collecting 2 seconds of isometric data in each dynamic exercise probably had no effect on the overall ratio. Further- more, exercises with movement were compared only with other exercises with movement, except that KE was compared with ISs and ISQA was compared with exercises with movement in subjects with PFP syndrome.

I had no method of quantifying my ability to control the speed of movement. Undoubtedly, some error ex- isted in subjects' ability to move at a constant speed with the metronome. Likewise, I had no better method of controlling isometric knee flexion positions than use of a standard goni- ometer. The error introduced by these shortcomings is unknown. These techniques, however, approximate clinical practice more than would a more elaborate method used to control speed or position.

The VMONL ratio was used in this study because it reflects the relative contributions of the VMO and VL. I believe an increase of VMO activity with a specific exercise is meaningless if the relative activity of the VL is un-

known, as both muscles may be increasing their activity the same amounts. Normalized EMG data are ratio data. A true absence of activity can exist, and ratios are used in normalization of the data.

Knee flexor activity may have occurred in some of the openchain exercises and most likely occurred in the closed-chain exercises. The purpose of this study was to compare results across similar exercises, regard- less of whether other activity was present. Rather than examine vastus muscle activity when no other activity was present, this study was designed to study exercises widely used in physical therapy.

VMOIVL Ratio

This study did not support the claims that certain commonly used exercises or patellar or tensor fascia lata muscle medial-ghde taping enhance VMO activity over VL activity. The only exercise to show a higher VMO/VL ratio in comparison with similar exercises was KEMR in comparison with KELR. This finding is in contrast to the commonly held hypothesis that hip lateral rotation, by creating a knee abduction torque, enhances the activity of the VM'9 but is consistent with the reported lack of preferential activation of the VMO during knee extension with a knee abduction torque.27~2~ Whether the small magnitude of increase in VMO/VL ratio (0.2) found with medial over lateral rotation of the femur is clinically significant is not known. Its significance most likely depends on the magnitude of the lateral tracking of the patella.

Likewise, preferential activation of the VMO over the VL is not consistent with this and other EMG studies of hip adduction27 or tibial rotationl8.29 with knee extension. Two investigations of openchain adduction exercises that did not require a simultaneous quadriceps femoris muscle contraction, however, did show preferential activation of the VM or VM0.18J9 Wheatley and Jahnke19 reported that VM action po- tentials occurred during hip adduction, but they did not quantlfy or statisti-

cally compare their data and their results could be in error due to volume conduction of adductor muscle activity to their widely spaced (22.54 cm [rl ia surface electrodes over the VM. Hanten and Sculthies' adduction exercise, although not requiring quadriceps femoris muscle activity, still elicited high levels of activity in both the VMO and VL.18 Perhaps conscious activation of the vastus muscles with adduction negates any benefit of adduction exercise to preferentially aai- vate the VMO. Wheatley and Jahnkel9 also reported greater VM activity during QS with leg lateral rotation. In addition, the findings of my study are not consistent with the theories that the VMO is selectively activated in a flexed position of the knee, during tibial medial or lateral rotation, or during subtalar joint pronation.6.9.18-23

Results of taping the patella and the tensor fascia lata muscle in my study are in contrast to McConnell's finding of an increased VMO/VL activity ratio in symptomatic subjects with such taping, even though subjects with PFP in my study reported greatly reduced pain during the SD exercise after medial-glide taping.16 McConnell did not report her EMG recording procedures. Whether her VMO data may have been contaminated by volume conduction of activity of nearby muscles to the VMO electrode, therefore, cannot be judged.

Some caution must be taken in inter- preting the findings of no effects of specific exercise or taping on the VMO/VL activity ratio because of the low number of subjects in this study. Ratio differences of 0.7 for ISs, 0.3 for QSs, and 0.6 for KEs, WS-SD, and WSls in subjects without PFP syndrome and of 0.7 for openchain exercises, 0.5 for closed-chain exercises, and 0.4 for taping in subjects with PFP syndrome were necessary to satisfy a statistical power of .80.3O True differences less than these ratios, therefore, could have been present without rejection of the null hypothesis. The magnitude of change in the VMO/VL ratio necessary for therapeutic effect is unknown. Certainly, the greater the

Physical 'Therapy / Volume 75, Number 8 / August 1995

increase in magnitude, the greater will be the medial pull on the patella.

Lack of preferential activation of the VMO over the VL due to exercise purported to produce such activation or due to patellar taping leads to the question of whether the VMO can be trained to selectively increase its activity. Studies of EMG biofeedback training for the VMO are needed to answer this question.

Because no dfierence in the VMONL ratio was found with patellar taping although pain was decreased an average of 94%, I question that taping decreases pain due to appropriate realignment of the patella. The ability to reliably determine patellar alignment is p0or.3~ Therefore, the ability to appropriately realign the patella is questionable. Furthermore, I found no evidence in the literature that patellar taping can maintain the position of the patella during exercise. The effect on PFP of placebo taping of the patella or of taping the patella with randomly chosen direction has not been studied. The positive effect of taping may be due to additional sensory input or the placebo effect. The effect of patellar taping, therefore, should be studied in a large group of subjects with PFP. Two groups of subjects without knowledge of taping theory randomly assigned to receive medial or lateral patellar taping can be studied using a blind research design.

Both subjects with and without PFP appeared to have similar VMO/VL ratios in open-chain exercise, whereas subjects with PFP appeared to have lower ratios in closed-chain exercise than subjects without PEP. Whether this apparent difference is statistically sigdicant or whether it is important is unknown. Statistical comparison in further studies would be beneficial.

VMO, VL, and AM Activity

Subjects in this study averaged higher VMO and VL activity during the QS exercises than in other open-chain exercises. They were at end range of knee extension for 5 seconds during the QS exercises but were either more

flexed or moving for at least 3 seconds of all other open-chain activities. As a result, subjects had the opportunity to produce high levels of EMG activity in the QS exercises while maintaining their test position. I suggest that they produced this high level of activity because they were well motivated. Attempts at increasing EMG activity during the other openchain exercises would have either increased the speed of movement (controlled with a metronome) or moved the leg from the isometric test position. Either of these activities would have resulted in dis- carding the data and repeating the exercise until the desired velocity or posture was attained. As a result, the EMG activity was lower for these exercises. Because 0thers27,3~ have found higher vastus muscle activity in QS than in straight leg raising, the QS has consistently been shown to be an excellent exercise for recruiting vastus muscle activity.

The increased activity in both the VMO and VL during IS15 over IS60 in both the subjects with and without PFP syndrome is expected due to the increased quadriceps femoris muscle demand at 15 degrees without preferential demand for VMO a~t iv i ty .~~~"~~~.33-35 This increased mechanical demand at 15 degrees is due to the combined effects of increased gravitational lever arm and decreased muscle length and lever arm of the quadriceps femoris muscle.

Because the WSlA tended to recruit

Conclusions

Whether in the subjects with PFP or in those without PFP, only one exercise resulted in a higher VMONL activity ratio over similar exercises. The KEMR showed a higher VMONL ratio than the KELR. Exercises more commonly prescribed to enhance VMO activity over that of the VL, however, failed to selectively activate the VMO. Further- more, the results of this study indicate that medial-glide taping of the patella or tensor fascia lata muscle does not alter the VMONL ratio.

Acknowledgments

I thank the following California State University, Long Beach, physical therapy students for their assistance in this project: Janet Froggatt, Anthony Granger, Cynthia Grauf, Kathy Harbert Greenwood, Michael Greenwood, Gregory R Jue, Mark Klem, Sonja Maul, Nancy Rhoan, Susan Royce, Stacy Sarnano, Ernie Sanchez, Milan Steijn, David Swink, Carol Whitmire, and Laura Olsen. I thank Michael Monahan for his question in class that inspired this research, and I thank Charles Felder, PT, OCS, instructor for M c C O M ~ ~ ~ seminars, who consulted with me on this project and who taught me the McComell taping technique.

References

1 Levine J. Chondromalacia patellae. Tbe Phy- sician and Sportsmedicine. 1979;7(8):41-49. 2 Outerbridge RE. Further studies on the aeti-

greater ~ 0 , w, and AM than ology of ch~ndromalacia patellae. J Bone Joint Surg [Brl. 1964;46:179-190.

the wS1 and because the SD and ISQA 3 Puniello MS. Iliotibial band tightness and recruited greater VMO, VL, and AM medial patellar glide in patients with patel- activity than the WS, the sumested lofernoral dysfunction. J Ortbop sports ~ h y s

benefit of these closedcharexercises Tber. 1993;17:144-148. 4 Fulkerson JP, Hungerford DS. Disorders of in persons with may be due to a the Patellofemoral loitzt. 2nd ed. Baltimore.

high level of coactivation of the knee ~ d : w i ~ ~ i i m s & wiikins; 1990 extensors and hlp extensors (AM) to 5 Malek MM, Mangine RE. Patellofemoral pain

better conkdl the femur. A comparison syndrome: a comprehensive and conservative approach. J Orthop Sports Phys Tber. 1981;2:

of lower-limb extensor muscle activity 108-116, ~- - - -

between closed-chain exercises that 6 McConnell J. The management of chondro- mandate multisegment control of the malacia patellae: a long-term solution. Austra-

lower limb and open-chain exercises lian Journal of Physiotherapy. 1986;32:215- q-9 LL3.

in subjects with Pm 'yndrome 7 Schutzer SF. Ramsby GR, Fulkerson JP. be beneficial. Computed tomographic classification of patel-

lofemoral pain patients. OrthoD Clin North Am. 1986;17:235-248.


8 Kettlekamp DB. Management of patellar malalignment. J Bone Joint Surg [Am). 1981;63: 1344-1348. 9 Mariani PP, Camso I. An electromyographic investigation of subluxation of the patella. J Bone Joint Surg [Brl. 1979;61:169-171. 10 Antich TJ, Brewster CE. Modification of quadriceps femoris muscle exercises during knee rehabilitation. Phys Zhw. 1986;66:1246- 1251. 11 Lieb FJ, Perry J. Quadriceps function: an anatomical and mechanical study using ampu- tated limbs. J Bone Joint Surg IAml. 1968;50: 1535-1548. 12 Weinstabl R, Schaf W, Firas W. The extensor apparatus of the knee joint and its periph- eral vasti: anatomic investigation and clinical relevance. Surg Radio1 Anat. 1989;ll: 17-22. 13 Bose K, Kanagasuntheram R, Osman MBH. Vastus medialis oblique: an anatomic and physiologic study. Orthopedics. 1980;3:880- 883. 14 Hehne IIJ. Biomechanics of the patellofemoral joint and its clinical relevance. Clin Orthop. 1990;258:7>85. 15 Slocum DB, Larson RL. Rotary instability of the knee. J Bone Joint Surg [Am). 1968;50:211- 225. 16 McConnell J. Training the vastus medialis oblique in the management of patellofemoral pain. In: Proceedings of the 10th International Congress of' the World Confederation for Phys- ical Zherapy; Sydney, Neu South Wales, Australia; 1987.

17 Doucene SA, Goble EM. The effect of exercise on patellar tracking in lateral patellar

compression syndrome. Am J Phys Med. 1992; 20:434-440. 18 Hanten WP, Schulthies SS. Exercise effect on electromyographic activity of the vastus medialis oblique and vastus lateralis muscles. ~ h y s Zher. 19%;70:561-565. 19 Wheatley MD, Jahnke WD. Electromyo- graphic study of the superficial thigh and hip muscles in L~ormal individuals. Arch Phys Med Rehabil. 1951;32:508-515. 20 Boucher JP, King MA, Lefebre R, Pepin A. Quadriceps femoris muscle activity in patellofemoral pain syndrome. Am J Phys Med. 1992;20:527-532. 21 Sczepanski TL, Gross MT, Cuncan PW, Chandler JM. Effect of contraction type, angu- lar velocitv and arc of motion on the VM0:VL ratio. J O h o p Sports Phys 7hw. 1991; 14:256- 262. 22 vanKampen A, Huiskes R. The three- dimensional tracking pattern of the human patella, J Otthop Res. 190;8:372-382. 23 McCulloch MU, Brunt D, Vander Linden D. The effect of foot orthotics and gait velocity on lower limb kinematics and temporal events of stance. J Orthop Sports Phys Zhw. 1993;17: 2-10. 24 Lehmkuhl LD, Smith LK. Brunnstrijm's Clinical Kinesiology. 4th ed. Philadelphia, Pa: FA Davis Co; 19837-8. 25 Soderberg GL. Kinesiology: Application to Pathological Motion. Baltimore, Md: Williams & Wilkins; 1986:60-61. 26 Knutson LM, Soderberg GL, Ballantyne BT, Clarke WR. Study of various normalization procedures for within-day electromyographic

data. Journal of Electromyography and Kinai- 010gy. 1994;4:47-59. 27 Karst GM, Jewett PD. Electromyographic analysis of exercises proposed for differential activation of medial and lateral quadriceps femoris muscle components. Phys 7hw. 1 9 3 ; 75286-299. 28 Andriacchi TP, Andersson GBJ, Onengren R, Mikosz RP. A study of factors influencing muscle activity about the knee joint. J m o p Res. 1984;1:266-275. 29 Duane-Cintra AI, Furlani J. Electromyo- graphic study of the quadriceps femoris in man. Electromyogr Clin Neurophysiol. 1981;21: 539-554. 30 Glantz SA. Primer of Bio-Statistics. 3rd ed. New York, N Y McGraw Hill; 1992:155-187, 311, 401-405. 31 Fitzgerald GK, McClure PW. Reliability of measurements obtained with four tests of patellofemoral alignment. Phys Zher. 195;75: 84-90. 32 Soderberg GL, Cook TM. An electromyographic analysis of quadriceps femoris muscle setting and straight leg raising. Phys Zher. 1983;63:1434-1438. 33 Basmajian JV. Muscles Alive. 5th ed. Balti- more, Md: Williams & Wilkins; 1985:324-332. 34 Eloranta V. Patterning of muscle activity in static knee extension. Electromyogr Clin Nac- rophysiol. 1989;29:369-375. 35 Moller BN, Krebs B, Tidemand-Dal C, Aaris K. Isometric contractions in the patellofemoral pain syndrome: an electromyographic study. Arch Orthop Trauma Surg. 1986;105:24-27.

Let PROFILE help you manage your professional development! Call 1.800/999.APTA* to enroll today!

'1-800/999-2782, ext 3395, 8:30 am-5:30 pm Eastern time UJ85

vastus medialis oblique vastus lateralis muscle activity ratios

Education