Grand Valley State University
ScholarWorks@GVSU
Masters Theses
Graduate Research and Creative Practice
1998
Knee Flexion Angle and its Influence on VMO:VL
Ratios During Isometric Quadriceps Contraction
Jeffrey P. Hendra
Grand Valley State University
William D. Allan
Grand Valley State University
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Part of the Physical Therapy Commons
Recommended Citation
Hendra, Jeffrey P. and Allan, William D., "Knee Flexion Angle and its Influence on VMO:VL Ratios During Isometric Quadriceps
Contraction" (1998). Masters Theses. Paper 396.
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KNEE FLEXION ANGLE AND ITS INFLUENCE
ON V M O iV L RATIOS
DURING ISOMETRIC Q U A D R IC E PS CON TRA CTIO N
By
Jeffrey P. Hendra SPT
William D. Allan SPT
T H E S IS
Subm itted to th e D epartm ent of Physical Therapy
at Grand Valley S ta te University
Allendale, Michigan
in partial fulfillment o f th e requirem ents
for th e degree of
MASTER OF SCIENCE IN PHYSICAL THERAPY
1998
THESIS COMMITTEE APPROVAL:
/I
Ch'air. Timothy Striidkler Ph.D.
Date
Memoer: Jane Toot Ph.D., PT
Date
4 /^3 /
Member: Justine Ritchie Ph.D.
Date
KNEE FLEXION ANGLE AND ITS INFLUENCE ON VMOrVL RATIOS
DURING ISOMETRIC QUADRICEPS CONTRACTION
ABSTRACT
Patellofemoral Pain Syndrome (PFPS) is a major cause of knee pain
and is caused by lateral patellar tracking. T reatm en t co n sists of
strengthening th e v astu s medialis obliquus (VMO). While many
exercises stre n g th e n th e VMO, sim ultaneous v astu s lateralis (VL)
strengthening o ften occurs and patellar malalignment remains. The
VMO m ust, therefore, be stren g th en ed independently or to a greater
extent than th e VL. Thus, th e VMOrVL ratio of activity m ust be
considered rath er th an VMO activity alone. This stu d y com pared
isometric knee extension electromyographically a t 0, 20, 60, and 90
degree angles to determ ine which angle produced th e g re a te st
VMOrVL ratio of activity. Results of this stu d y indicated no
significant differences among angles te s te d for VMOrVL ratio during
isometric knee extension. Further research is needed to investigate
th e possibility of significant associations b etw een VMOrVL ratios
and gender, pathology, and angles not included in this study.
ACKNOWLEDGMENTS
The investigators would like to thank th e following individuals
for their time and assistan ce:
Dr. Tim Strickler and Dr. Jane Toot
for direction, input and su p p o rt, Dr. Justine Ritchie, Dr. Neal Rogness
and Todd Uvergood for making se n se of a thousand different numbers
with no apparent meaning. We would also like to thank Dr. John Peck
for ordering supplies, Jim S c o tt for providing a ssista n c e in th e lab,
and Kathy “The Connection” Johnstone and Kathy “Wiz” Wagner for
introducing us to Myosoft.
Special thanks to Sheila Allan for her
com puter expertise and our friends and families for providing
support, patience, and understanding throughout th e en tirety of this
p ro ject.
11
TABLE OF CONTENTS
Page
ABSTRACT...............................................................................................................i
ACKNOWLEDGMENTS......................................................................................... ii
PREFACE.................................................................................................................. V
D efinition o f T erm s................................................................. v
LIST OF TABLES...................................................................................................vii
LIST OF FIGURES............................................................................................. v iii
CHAPTER
INTRODUCTION..................................................................................1
2. LITERATURE REVIEW..................................................................... 4
P revalence and C auses o f PFPS..............................................4
Anatomy o f th e P a te llo fe m o ra l J o i n t .................................7
Role o f th e VMO..........................................................................9
S e le c tiv e R ecru itm en t o f th e VMO....................................10
3.
METHODOLOGY...............................................................................20
S u b je c ts .................................................................................... 20
D esig n .........................................................................................20
P ro c e d u re .................................................................................. 21
In stru m en ta tio n ........................................................................22
V alid ity and R e liab ility ......................................................... 23
4.
RESULTS/DATA ANALYSIS........................................................24
iii
T e c h n iq u e s................................................................................ 24
H ypo th esis/R esearch Q uestion............................................ 26
O ther Findings and O b serv atio n s o f I n te r e s t.................. 27
5. D iscussion and Im p lic a tio n s .................................................... 30
D iscussion o f Findings............................................................30
A pplication o f P ra c tic e ..........................................................31
L im ita tio n s ............................................................................... 32
S u g g estio n s For F u rth er R esearch...................................... 34
C o n c lu sio n .................................................................................35
REFERENCES....................................................................................................... 37
APPENDIX A - INFORMED CONSENT FORM................................................... 42
APPENDIX B - DATA COLLECTION SHEET..................................................... 45
APPENDIX C -PROPOSAL SUMMARY FOR HSRC.......................................... 47
IV
PREFACE
Definitions o f Term s
Patellofemoral Pain Syndrome (PFPSVpain resulting from a
dysfunction of th e patella’s ability to track in th e femoral groove
isom etric quadriceps s e ts - a contraction o f th e quadriceps in which
tension is developed b u t no joint m ovem ent or change in muscle
length occurs. This contraction is perform ed a t terminal knee
extension
sh o rt-arc quadriceps s e ts - an exercise w here th e leg is moved
through the last 35 d egrees of extension
isom etric knee extension-a contraction of th e quadriceps in which
tension is developed b u t no joint m ovem ent or change in muscle
length occurs. This contraction can be perform ed a t any angle.
0 -a n g le-the acu te angle formed betw een intersecting lines drawn
from th e anterior-superior iliac spine through th e mid-portion of
th e patella, and from th e anterior tibial tu b ero sity through th e mid
patella. Normally 15 d eg rees
subluxatlon-an incom plete or partial dislocation
pes planus-condition of th e foot in which th e medial longitudinal
arch is decreased. Also known as pronated or flat foot
genu recurvatum-a condition characterized by a hyperextension of
th e knee
biofeedback-training technique utilizing visual and audio o u tp u t
regarding muscle activity via electrom yography. Subjects are,
th erefore, trained to selectively stim ulate or inhibit a specific
m uscle
electrom yography fEMGVtechnique in which m uscle activ ity is
d e te c te d and recorded through an electrical medium
hip adduction-m ovem ent of th e fem ur tow ard th e midline of th e body
goniom eter-a device used to m easure jo in t angles
VI
LIST OF TABLES
Table
Page
1.
D escriptive S t a t i s t i c s Table For Avg VMOiVL
M easu rem en ts.................................................................................. 27
2.
D escriptive S t a t i s t i c s Table For Avg VMO:VL
by G en d er........................................................................................... 28
VI I
LIST OF FIGURES
Table
1.
Page
Sam ple o f Noraxon M yosoft O u tp u t................................................2 4
VIII
CHAPTER. 1
INTRODUCTION
According to Malek and Mangine,i “Patellofem oral Pain
Syndrome (PFPS) is th e number one cause of knee pain in a majority
of th e knee clinics in sp o rts medicine cen ters around th e country.”
Many researchers agree th a t th e major underlying cause of PFPS is a
malalignment of th e patellofem oral joint causing th e patella to
track laterally in th e patellofem oral groove.
27
Malalignment is due
to a variety of causes. T hese cau ses include abnormal architecture
and articulation of th e patellofem oral joint,
retinacu lu m ,
2,4-6,a
2.4-6
a tig h t lateral
and a m uscular imbalance betw een th e vastus
medialis obliquus (VMO) and th e v astu s lateralis (VL). 2,5.6.9 The
result of th e se abnormalities is a laterally tracking patella causing
pain for th e patient.
The VMO has been id e n tifie d a s th e only s tr u c tu re w ith the
ability to pull th e patella medially, lo.n
Theoretically, strengthening
of th e VMO will correct m alalignm ent thus relieving pain. Exercises
recom m ended by researchers and therapists to stren g th en th e VMO
include isom etric quadriceps s e ts ,
1
1,12-17
straig h t leg raises,
1.12-15.17-
19 sh o rt-arc quadriceps s e ts , i.i8,i9 isom etric knee extension, is-zo and
various ty p es of sq u ats and s te p ups.
Many of th e s e protocols
have been found to successfully stren g th en th e VMO. However, while
strengthening th e VMO, th e se exercises may also stren g th en th e VL
to th e sam e degree. Even though th e VMO is stren g th en ed , it may
still n o t be able to pull th e patella medially becau se of th e
sim ultaneous strengthening of th e VL pulling th e patella laterally.
For an exercise to be efficient in altering malalignment and reducing
pain, it is necessary to stren g th en th e VMO independent of th e VL or
a t le a st stren g th en it to a significantly g reater d eg ree th an th e VL.
When identifying an exercise th a t co rrects malalignment, th e
researcher should look a t th e VMOiVL ratio o f activity rath er than
simply VMO activity.
Finding an e x e rc ise th a t can s p e c ific a lly stre n g th e n th e VMO
and th u s relieve pain would be of g reat benefit to many people. It
has been estim ated th a t th e incidence of PFPS in th e general
population is as high as one in four.
21
A proven protocol in
com bating PFPS would also save th e th erap ist much tim e and
anguish and possibly influence reim bursem ent by third party payors.
S ev eral au th o rs have recom m ended an is o m e tric co n tractio n o f
th e quadriceps to facilitate strengthening of th e VMO. Many believe
th a t this contraction should be perform ed a t terminal knee
extension. 1,12-17 O thers believe th a t isom etric quadriceps
contractions should be performed a t 20 d egrees of flexion. 1s i9 More
recently researchers have su g g e sted th a t th e se isom etric quadriceps
contractions should be performed betw een th e range of 60 and 90
d eg rees of knee
f le x io n .i 9.22,23
The problem is th a t th e re is little
scientific d ata th a t indicates th e VMO is stren g th en ed to a g reater
degree than th e VL in any o f th e se ranges of motion (ROM) during an
isom etric contraction. The purpose of this study is to compare th e
activity of th e VMO relative to th e activity of th e VL a t various
points betw een 0 and 90 degrees of knee flexion during isometric
contraction. Our hypothesis is th a t isom etric quadriceps
contractions betw een 60 and 90 d eg rees of flexion will result in
larger VMOiVL ratios than a t o th er ranges of motion in th e knees of
healthy college age males and females.
CHAPTER 2
LITERATURE REVIEW
The majority of this literature review relates to th e exercises
and theories surrounding th e selective strengthening of th e VMO. For
a b e tte r understanding of th e s e exercises and theories, it is
im portant th a t the reader have a background in the prevalence and
causes of PFPS, th e anatom y of th e patellofemoral Joint, and th e
role of th e VMO.
Prevalence and Causes of PFPS
P atello fem o ral pain syndrom e (PFPS) p re se n ts a s a sig n ific a n t
problem for many ath letes involved in sporting activities and is
classified as a dysfunction of th e patella's ability to track properly
in th e femoral groove.? PFPS has been called th e num ber one cause of
knee pain in a majority of th e knee clinics in sports medicine
cen ters around th e
c o u n t r y ,1.2.8,21,24
population is as high as one in
and its incidence in th e general
fo u r .z i
This syndrome is
characterized by pain in th e anterior portion of th e knee and can be
attrib u ted to many different causes. The end result, however,
appears to be excessive lateral pressure on th e patellofemoral (PF)
articulatio n .6
One o f th e m a jo r c a u se s o f PFPS I s m alalignm ent o f th e PF
jo in t.1-6.8 Kramer 6 lists th e four main causes of malalignment as 1)
architectu ral abnorm alities of articulation, 2) muscle im balance
betw een VMO and VL, 3) retlnacular abnormalities, and 4 ) an
increased Q-angle. Kettlekam ps ag rees with th ese sam e four cau ses
adding laxity of th e medial retinaculum and atrophy of th e VMO as
underlying causes of malalignment. Fulkersons s ta te s th a t PF
malalignment may cause rep eated mild to m oderate subluxation and
relocation of th e patella which cau ses chronic strain and tightening
of th e lateral retinaculum. This in turn increases th e Q-angle which
can lead to PFPS.
O ther cau ses o f an in c re ase d Q -angle include fo o t pronation,
pes planus, genu recurvatum , and wide hips.6 Women, therefore, are
more prone to PFPS due to larger pelvic width.
O ther m ajor co n d itio n s leading to PFPS include d eg en erativ e
disease, repeated m icrotrauma, a c u te severe traum a,i iliotibial band
tig h tn e ss,8 and medial retinacular rupture.^ These conditions may
cause lateral tig h tn ess and medial w eakness of connective tissu e
surrounding th e patella predisposing th e p atient to a bony
malalignment betw een th e femur and tibia. This bony malalignment
will cause th e patella to track improperly in th e patellar groove.
Thus, it is evident th a t a proper balance betw een medial and lateral
stru c tu re s m ust be m aintained for maximal alignment of th e PF
jo in t.
A balance o f s tre n g th betw een th e VMO and VL m u scles i s
imperative for this balance to be maintained.^
Individuals affected
by PFPS differ from healthy individuals in regards to their VMOiVL
activation p attern s. While th e VMOiVL activation p attern s of the
healthy individual are close to equal, th e p a tte rn s of PFPS p atien ts
show decreased activation of th e VMO during EMG assessm ent. 24.25
Conservative tre a tm e n t is, therefo re, aimed a t selective
strengthening of the VMO.
Due to th e p revalence o f th is syndrom e i t may be assum ed t h a t
an effective exercise protocol is currently in widespread use. In
truth, however, no such protocol ex ists due to lack of evidence of
exercises th a t selectively ta rg e t th e VMO. Thus, PFPS also poses a
problem for th e clinician attem p tin g t o tr e a t th is disorder.
Anatomy- of the Jatelloffimocal-Joint
The anatom y o f th e PF j o i n t a ls o m akes th is syndrom e
particularly difficult to tr e a t. According to Norkin and
L e v a n g ie ,2 6
"to g e th e r with th e femoral surface on which it sits, th e
patellofem oral joint is...the least congruent joint in th e body."
T hese au th o rs also define th e patella as th e largest sesam oid bone
in th e body which functions as an anatomical pulley to reduce
friction betw een th e quadriceps tendon and th e femoral condyles. In
order to perform this function w ithout limiting knee motion, th e
patella m u st slide on th e femoral condyles while remaining se a te d
betw een them in th e intercondylar
g r o o v e .2 6
This groove corresponds
to th e vertical ridge on th e posterior a s p e c t of th e patella thereby
providing a tracking m echanism for th e PF joint to maintain proper
alignm ent. This mechanism is under control of two restraining
m echanism s crossing a t right angles: a group of tran sv erse
stabilizers and a group of longitudinal stabilizers. For simplicity,
th e longitudinal stabilizers will be defined as the quadriceps tendon
superiorly and th e patellar tendon
in fe r io r ly .2 6
Norkin and
L e v a n g ie 2 6
have described th e tran sv e rse stabilizers as th e medial and lateral
8
extensor (patellar) retinaculae. In general, th e function of th e
retinaculae are to connect th e patella to dense connective tissues
around th e knee. Laterally th e s e include th e fascia lata and iliotibial
band as well as th e v astu s lateralis muscle. Similarly, th e medial
retinaculum functions to connect dense connective tissue and th e
v astu s medialis to th e medial patellar border .26 Lieb and Perry”
found th e pull of th e VL to be 12 to 15 degrees lateral to th e long
axis of th e femur, with th e distal fibers even more angulated. The
angulation of th e VM pull depends on which portion of th e muscle is
assessed. The upper fibers of th e VM are angulated 15 to 18 degrees
medially to th e femoral sh aft, while th e distal fibers are angulated
approximately 50 to 55 d eg rees medially. It is because of this
drastic difference in fiber orientation of th e upper and lower
portions of th e VM muscle th a t it is categorized into two
com ponents: v astu s medialis longus (VML) w hose fibers originate
from th e intertrochanteric line and medial lip of th e linea aspera of
th e femur and v astu s medialis oblique (VMO) 26 w hose fibers
originate primarily from th e adductor magnus tendon. 27.2s This
difference in fiber orientation betw een th e VMO and VL may be a
reason why difficulties in tre a tm e n t have been experienced.
Role of th e VMQ
The ro le o f th e VMO a s a dynam ic m edial s ta b iliz e r providing
proper patellar alignment is strongly su p p o rted in th e
lite r a tu r e .10.11.27.29.30 Lieb and Perryn s ta te th a t th e only selective
function attributable to th e VMO is patellar alignment.
A second and q u estionable ro le o f th e VMO i s te rm in al knee
extension. Fiebert e t al3i claim th a t th e VMO becom es m ost active
near terminal knee extension. Basmajianio also found th a t th e VMO
appears to increase activity tow ard th e end of unweighted
extension, b ut found no significant difference betw een th e VMO and
o th e r quadriceps com ponents during sq u attin g exercises. This is
supported by other research th a t claims th e b est exercises for PFPS
are ones performed with full knee extension. 12.17.19
D espite th e se claim s, o th e r re se a rc h in d ic ates th e VMO does
n o t account for th e last few degrees of terminal extension .22 Lieb
and Perry
11
report th a t all four quadriceps heads increase activity
in terminal extension. They s ta te th e VMO helps perform terminal
extension but does not individually account for the final 15 d eg rees.
10
In another study by Brownstein e t
a l, 23
it was found th a t th e VMO is
actually least active in th e ex ten d ed position. Finally, a stu d y by
Ingersoll and Knight32 show ed th a t terminal extension exercises do
n o t produce medial relocation of th e patella. Interestingly, th e y
reported th a t th e s e exercises actually seem to predispose p atien ts
to PFPS.
Selective Recruitm ent of th e VMO
C urrently, biofeedback h as th e m o st prom ise in f a c ilita tin g th e
selective recruitm ent of th e VMO. Wise e t
al.33
studied th e e ffe c ts of
biofeedback in conjunction with exercise (straig h t leg raise, quad
s e ts , and terminal knee extension) and functional activities
(ambulation, bicycling, and sta ir climbing). Results of this stu d y
show ed th a t biofeedback is effectiv e in producing significantly
g re a te r activation of th e VMO than VL in all activities.
Ingersol and Knightaz used a protocol established by Wise e t
al.33 and compared th e effects of biofeedback to th e effects of a
progressive resistan ce routine using a sh o rt arc quadriceps exercise.
Their study su g g e sts th a t, “quadriceps group stren g th changes are
n o t enough to fully rehabilitate patellar tracking dysfunctions. The
n
use of EMG biofeedback training to selectively stren g th en th e v astu s
medialis obliquus ap p ears to be essen tial in correcting faulty
patellar tracking." Thus it appears from th e literature th a t th e
incorporation o f biofeedback into a rehabilitation program is
extrem ely advantageous. Biofeedback, however, is not often
available for a hom e program, and research into th e effectiveness of
exercises w ithout biofeedback is still n eeded.
The McConnell tap in g and e x e rc ise p ro to co l i s an o th er avenue
in th e rehabilitation of PFPS which holds potential.^ In this protocol,
th e patella is ta p e d into proper alignm ent. Once taping is com pleted,
th e p atien t perform s a number of w eightbearing exercises with
em phasis on th e eccentric contraction of th e quadriceps group.
During th e contractions th e patient is in stru cted to contract th e
VMO and to relax th e lateral ham strings and th e VL as much as
possible. The hip is also adducted during exercise to, theoretically,
aid in selective VMO recruitm ent. The use of McConnell taping to
increase VMO activity is validated by King e t al..34 King e t al. found
th a t mechanically altering th e alignm ent o f th e patella facilitates
th e neural drive of th e VMO and reduces th e activity of the VL. At
12
this tim e, how ever, few th erap ists are well versed in patellar
taping techniques. Also, more research needs to be done to verify
McConnell’s claim of a success rate of over 90% .
B ecause o f th e VMO’s a tta c h m e n t to th e ad d u cto r magnus
tendon, many researchers believe th a t hip adduction can be used to
help selectively stren g th en th e VMO. They believe this can be
accom plished through either isolated hip adduction or hip adduction
accom panied by a quadriceps contraction. H anten and Schulthiesss
had su b je c ts perform maximal isom etric hip adduction against a
resistance pad. M easurements of VMO and VL activity w ere taken and
results w ere expressed as a percentage of th e maximal voluntary
isom etric co n tractio n (MVIC). Significantly g re a te r activity was
found in th e VMO (61.75% ) compared to th e VL(45.63%). From this
research it appears th a t isom etric hip adduction selectively
stre n g th e n s th e VMO relative to th e VL. Westfall and Worrell,20
however, criticize th e se findings questioning th e high ratio of VMO
activity w ithout knee extension. Thus, more research needs to be
done to confirm th e se findings and determ ine w hether a hip
adduction protocol can increase th e VMOiVL ratio with any
13
clinical significance.
The influence o f hip adduction on th e VMO during q u ad ricep s
contraction is less clear. King e t al.34 te s te d p atien ts concentrically
and eccentrically a t 30 degrees per second over a range o f motion of
10 to 100 degrees with a Kincom dynam om eter. Testing su b jects
with and without concurrent hip adduction th ey found th a t 1 ) hip
adduction had no effect on the activity of th e VMO and 2) th e VMO:VL
ratio remained unchanged.
G rabiner e t al.36 monitored VMO and VL activity of su b jects
under tw o s e ts of conditions. First, th ey simultaneously perform ed
hip adduction and an isometric quadriceps contraction a t 20 degrees
of flexion. Second, th ey performed th e isom etric contraction w ithout
hip adduction. The researchers found th a t th e effect of hip adduction
was n o t significant.
Hodges and Richardsons? refu te th e notion th a t hip adduction
has no influence on selective strengthening of th e VMO. In their
research, “hip adduction was superim posed onto th e contraction of
th e quadriceps femoris in a weight bearing and a non-weight bearing
position a t th ree levels of hip adduction force.” They found VMO
14
activity increased relatively m ore than th e VL with th e addition of
each level of hip adduction in w eight bearing. The results w ere not
as dram atic in non-weight bearing with differences being seen only
a t maximal hip adduction. Still, their research indicates th a t hip
adduction is advantageous to VMO strengthening.
Obviously, w ith all th e d isc re p a n c ie s in th e lite r a tu r e , m ore
research is needed to determ ine th e actual role of hip adduction.
Even though th e current body o f literature is limited, research
seem s to indicate th a t th e e ffe c ts of hip adduction may differ
depending on th e ty p e of exercise being performed.
Iso k in etic knee extension i s another ex e rc ise o fte n p rescrib ed
in th e trea tm en t of PFPS. Sczepanski e t al.38 investigated th e
effects of arc of motion, angular velocity, and type of contraction on
VMO:VL ratio during isokinetic knee extension. They found a
significant difference in VMOrVL ratio depending on th e arc of
motion. A significantly g reater VMO:VL EMG ratio occurred a t 60-85
degrees of flexion than at 3 5 -6 0 or 10-35 degrees of flexion.
Results also indicated concentric contractions produce a g re a te r
VMOrVL ratio than eccentric contractions and faster velocities (1 2 0
15
degrees per second) enhance VMO:VL ratio b e tte r than slower
velocities (6 0 degrees p er second). These findings w ere supported by
th e work of Boucher e t
al.22
who compared th e VMO and VL activity
betw een 0 and 90 d eg rees. They specifically m easu red EMG activity
at 15, 30, and 90 degrees and concluded th a t VMO:VL ratios are
g re a te s t a t 90 deg rees o f knee flexion and th e VMO is facilitated in
th a t specific ROM.
W hile dynam ic e x e rc is e s a re usually p re s c rib e d in th e la te r
sta g e s of rehabilitation, many researchers have recom m ended a
protocol consisting of isom etric quadriceps c o n tra ctio n s during th e
initial s ta g e s .
1,12.14.18-20
The belief is th a t isom etric quadriceps
contractions will maintain or enhance VMO s tre n g th during th e
period when dynamic exercise may still be to o painful to perform.
As Woodall and Welshis s ta te , “th e initial p h ase o f rehabilitation is
to increase joint motion, and to g e t th e VMO under good, active,
voluntary control, and to d ec re ase patellofem oral jo in t irritation.”
Many th e r a p is ts o f th e p a s t have a tte m p te d to stre n g th e n th e
VMO by isom etric quadriceps contractions a t full knee extension.
This w as based on older research which claimed th a t th e VMO was
16
chiefly responsible for th e last 10 to 15 d eg rees of knee
e x te n sio n s 1.39 Using am putated limbs and an elaborate pulley sy stem
to replicate th e force vectors of th e quadriceps heads, Lieb and
P e rry 11 dem onstrated th a t th e VMO did n ot contribute any more than
th e o th er quadriceps heads to knee extension. They found th a t the
only selective function attributable to th e VMO was patellar
alignm ent. This research was more recently supported by an
electrom yographical study by Basmajian.io He concurs th a t th e only
selective function of th e VMO is patellar alignment. Basmajian also
found th a t th e VMO appeared to increase activity toward th e end of
extension in unweighted limbs, b u t th is activity was not greatly
different from th a t of th e other heads of th e quadriceps. This
indicates th a t even though VMO activity is increased, isometric
quadriceps contraction a t 0 to 15 d eg rees of knee flexion is not an
efficient exercise for PFPS because th e VMO:VL ratio is not changed
sig n ific a n tly .
O ther a u th o rs have p rescrib ed is o m e tric quadriceps
contractions a t 20 degrees of flexion.is.i9 This position is chosen
because, “it is here th a t th e patella actively begins to centralize in
17
th e femoral sulcus. With more flexion, about 45 degrees, th e main
arthritic zones of th e patella are p resen t so this area is avoided,
especially if pain or specific pathology is p re se n t.”i9 While this
position is successful a t reducing pain, th e re is no research to
indicate th a t it is efficient a t increasing th e VMO:VL ratio.
W e stfall and Worrell2o recom m end isom etric quadriceps
contractions in th e range of 60 to 85 degrees of flexion based on
research by Brownstein e t
a l.23
and Boucher e t
aL.22
Brownstein e t
al. atte m p te d to locate th e position of peak torque of th e quadriceps
complex to establish a normalization protocol. Subjects perform ed
maximal isometric contractions every 10 degrees from 10 to 90
d eg rees of knee flexion. The researchers recorded th e to rq u e of each
individual quadriceps head as well as th e torque of th e quadriceps
complex as a whole. The study showed peak VMO torque occurred
betw een 60 and 90 degrees of knee flexion. While Brownstein e t al.
recorded th e torque of the VMO and VL, th ey neglected to calculate
th e VMOiVL ratios. Boucher e t
al.22
found, similar to th e Brownstein e t
performed an isokinetic stu d y and
al.23
isom etric study, th a t peak
torque occurred at 90 degrees of flexion. Although Brownstein
18
e t al. did not figure th e VMO:VL ratio, and th e Boucher e t al. stu d y
was done isokinetically, Westfall and Worrelizo still believe th a t 60
to 90 deg rees of knee flexion is th e optimal position for selectively
strengthening th e VMO during an isom etric quadriceps contraction.
Biofeedback and McConnell Taping hold p ro m ise in th e
tre a tm e n t of PFPS. Research also shows th a t dynamic exercises
such as isokinetic knee extension and weight bearing eccentric
exercises may selectively strengthen th e VMO. Thus, th e s e exercises
would be useful in th e later sta g es of PFPS tre a tm e n t.
T rad itio n ally , iso m e tric e x e rc ise s have been p resc rib e d in th e
early sta g e s of PFPS rehabilitation. The literature show s th e re is no
consensus on th e m ost beneficial position to perform th e se
isom etric quadriceps contractions. During this literatu re review th e
only research found on VMO:VL ratio during isom etric quadriceps
exercise was a study by
C ern y.24
Cerny compared VMO and VL
activity a t 15, 45, and 60 degrees of knee flexion. Results indicated
th a t maximal VMO and VL activity occurred a t 45 d egrees. There
was, however, no significant difference in th e VMOiVL ratio a t any of
th e th ree positions.
19
Based on th e lite r a tu r e , th is stu d y exam ined VMO:VL ra tio s a t
0, 20, 60, and 90 d eg rees of knee flexion and com pared obtained
values. It is th e in ten t of this study to add to th e negligible body of
research on VMO:VL activity and to further define th e b e s t position
for selectively stren g th en in g th e VMO during isom etric contraction.
CHAPTER 3
METHODOLOGY
SuWects
S u b je c ts fo r th is stu d y co n siste d of 49 m a les and fem ales
ranging from 21 to 37 years of age with no history of hip or knee
problems. The subjects, 31 fem ales and 18 males, w ere selected via
a sam ple of convenience using physical therapy s tu d e n ts enrolled a t
Grand Valley S ta te University. All testin g was perform ed in the
Human Performance Lab of th e physical therapy d ep artm en t a t th e
Allendale cam pus of Grand Valley S ta te University.
Qfisiga
S im ultaneous EMG readings w ere taken o f th e VMO and VL
during isom etric contraction a t angles of 0, 20, 60, and 90 degrees
of knee flexion. From th e EMG values, a VMO:VL ratio was established
for each trial. T hese ratios were then averaged to establish
a mean
VMO-.VL ratio for each of th e designated te s t angles. Finally, a
rep eated m easures analysis of variance te s t was used to determ ine
if a statistically significant difference exists among th e VMO:VL
ratios of th e four angles.
20
21
Procedure
Following approval by th e Human S u b jects Review Board o f
GVSU, su b jects were asked to sign a consent form informing them
of their role in this study. Consenting subjects were te s te d
isometrically a t arcs of 0, 20, 60, and 90 degrees of knee flexion. To
reduce any effects of fatigue or learning, th e order in which th e
angles were te s te d was se lec ted randomly by each su b ject. This was
accomplished by writing each angle on a separate piece of paper.
The papers were folded to conceal th e number, and all four pieces of
paper were placed into a hat. The subject was then in stru cted to
tak e one piece of paper out of th e h at and read th e num ber w ritten on
it. The order th e numbers w ere pulled out of th e hat by th e su b ject
w a s th e o rd er in w hich each angle w a s te sted .
Once th e o rd er o f an g les to be te s te d w as s e le c te d , th e
su b je ct's leg was shaved over th e belly of the VMO and distal VL
using a disposable razor. Each shaved area was then rubbed clean
with an isopropyl alcohol sw ab to sanitize th e skin and maximize
electrode adherence. While th e su b ject was seated in a CYBEX te s t
chair, th e researcher placed self-adherent surface electro d es to
22
each of th e se designated areas. The electro d es were then plugged
into lead wires connected to a com puter and th e EMG data fed into
MYOSOFT EMG softw are for Windows. The su b ject's knee was then
positioned a t th e first randomly se lec ted angle using a standard
goniom eter. The padded resistance bar from th e CYBEX was placed
tw o finger widths proximal to th e medial malleolus a t th e anterior
ankle of th e te s t leg for resistance and to maintain th e knee a t th e
designated t e s t angle. When instructed, th e su b ject performed a
maximal isom etric contraction of th e quadriceps femoris for th re e
seconds against th e padded resistance bar. Subjects performed th ree
consecutive trials a t each angle with a one minute rest betw een
tr ia ls .
Instrum entation
A Noraxon Myosystem 1200 R esearch EMG u nit w as used f o r th e
collection of raw d ata. D isposable silver-silver chloride selfadhering electrodes measuring one and th ree quarters inches were
used on all su b jects. M easurem ents o f knee flexion were taken using
a standard goniom eter. The goniom eter was aligned to specific
anatomical landmarks su g g ested by Norkin and White with th e
23
fulcrum of th e goniom eter over th e lateral epicondyle of th e femur,
th e proximal arm aligned with th e g reater tro c h a n te r and th e distal
arm aligned with th e lateral malleolus.
Validity and Reliability
R esearch h a s show n a lin ear re la tio n sh ip b etw een m uscle
tension and EMG microvolt output.^w s The validity of using EMG
surface electro d e s as a m easurem ent of isom etric muscle tension is
also well estab lish ed in th e Iiterature.i7.23
To fa m ilia riz e th e t e s t e r s w ith th e Noraxon Myosoft 1200
Research EMG unit, a pilot study with 18 su b je cts w as performed.
During th e actual study, th e same te s te r positioned electrodes,
m easured angles of knee flexion, and gave instruction to all 49
subjects. The order of th e testing angles was se le c te d randomly to
decrease th e e ffe c ts o f fatigue and improve reliability.
CHAPTER 4
RESULTS/DATA ANALYSIS
Ifichniques
EMG d a ta w a s c o lle c te d on 31 fe m a le s and 18 m ales using th e
Noraxon Myosoft 1 2 0 0 . Param eters for th e unit were s e t with a
trigger level of 10 m icrovolts, an o n se t tim e of 100 milliseconds,
and a su b sist tim e of 2 0 milliseconds. The Myosoft softw are package
analyzed all data, giving a value in m icrovolts-squared of th e to ta l
area underneath th e graphical representation of th e contraction and
displaying th e values in bar graph form.
A rea (uVz) = Xi ([EMG]i x [Sam pling ln terv al]i)
VM0=1 ZOOuW
Figure
VL=800uV2
1. Representation of Noraxon Myosoft EMG output.
24
25
These values were then transferred by hand onto a data collection
sh e e t (see Appendix B). The d ata were analyzed by a stu d e n t from th e
GVSU Statistics D epartm ent using a repeated m easures analysis of
variance te s t on SAS softw are.
A one-w ay w ith in s u b je c ts ANOVA w as conducted w ith th e
facto r being angle and th e d ependent variable being th e average ratio
of VMO:VL The descriptive sta tistic s for th e d ependent variable
broken down by th e angle are presented in Table 1. One of the
assum ptions for th e one-way w ithin-subjects ANOVA is th a t the
dependent variable is normally distributed in th e population for
each level of th e w ithin-subjects factor (angle). This was not
satisfied at each of th e angles (all tended to follow a right-skewed
distribution). To adjust for th e violation of this assum ption, the
square root transform ation o f th e dependent variable was used. This
m eans th at th e dependent variable used in th e one-way withinsubjects ANOVA was th e square root of th e average ratio of VMO:VL.
Another assum ption fo r th is one-w ay w ith in -s u b je c ts ANOVA
is th e homogeneity of variance assum ption which, according to
Portney and Watkins'^ “s ta te s th a t th e variances within each of
26
th e s e s e ts of difference sco res will be relatively equal and
correlated with each o th e r.” According to Mauchly’s criterion, this
assum ption was n ot satisfied.
To a d ju s t fo r th e f a c t th a t th is assum ption w a s n o t s a tis f ie d ,
th e degrees of freedom for th e F-dlstrlbutlon were ad ju sted by th e
G reenhouse-G elsser correction factor-^. The results for th e repeated
m easures ANOVA, th erefo re. Indicate th a t th ere Is not a significant
angle effect (F= 2.26, dfl = 2.14, df2 = 102.73, Adj G-G value = .106).
Therefore, th ere Is n ot sufficient evidence a t th e 0.0 5 level to say
th a t there Is a difference In th e average VMO:VL ratio am ong th e
angles studied.
Hypothesis/R esearch Question
Our original h y p o th esis th a t VMOiVL ra tio s w ould be la rg e s t I n
th e sixty to ninety deg ree range was not supported by th e statistical
analysis. Testing th e null hypothesis, th a t there would be no
difference betw een mean VMO:VL ratios betw een angles, a P-value of
0 .106 was calculated. Because this value Is g reater than .05, there
Is not sufficient evidence to conclude th a t th ere Is a difference In
th e mean average VMO:VL ratio among the angles studied. This may
27
be due to th e fact th a t a larger sam ple size is necessary to d e te c t
small differences betw een th e VMO:VL ratios. A larger sam ple size
would reduce th e standard deviation (SD) and b e tte r determ ine if th e
small differen ces are statistically significant. T hese small
differences are shown in Table 1.
Table 1.
D e sc rip tiv e S ta tis tic s T able fo r Avg VMQ:VL M e a su re m e n ts
SD
Qi
03
Min
Max
.77
.52
.50
1.32
.06
2.46
.94
.81
.70
.55
1.19
.04
4.13
49
.82
.67
.61
.45
1.17
.01
2.90
49
.86
.76
.53
.52
1.13
.04
2.47
Angle
N
Mean
Median
0
49
.89
20
49
60
90
Other Findings and .Observations of Interest
During d a ta co llectio n w e found se v e ra l unexpected ite m s o f
in te re st. Through informal conversation with su b jects betw een t e s t
trials, we found th a t subjects exhibiting high VMOiVL ratios o ften
reported participating in sports. T here were, however, a few
28
su b je cts who w ere not involved in sporting activities who displayed
VMOrVL ra tio s similar to “athletic” s u b je c ts.
We a lso n o ticed a d ifferen ce in VMOrVL r a tio s betw een genders.
Generally, m en te n d ed to have higher m ean ratios a t all angles
com pared to women (se e Table 2). Again, this was not tru e for all
Table 2.
D e sc rip tiv e S ta tis tic s Table fo r A vg VMOrVL by G ender
N
Mean Median
SD
Qi
03
Min
Max
Angle 0
m ale
18
1.21
1.25
.54
.80
1.54
.28
2.46
fem ale
31
.70
.55
.41
.44
.88
.06
1.66
m ale
18
1.32
1.23
.92
.79
1.48
.04
4.13
fem ale
31
.72
.73
.40
.41
1.01
.05
1.88
m ale
18
1.13
.90
.74
.65
1.58
.11
2.90
fem ale
31
.63
.53
.44
.30
.89
.01
1.52
m ale
18
1.10
.91
.67
.66
1.58
.10
2.47
fem ale
31
.71
.72
.37
.40
1.05
.04
1.55
Angle 20
Angle 60
Angle 90
female su b je c ts since one of th e highest ratio s was reg istered by a
29
tw enty-four year old female who had not been active in sports for an
eleven m onth period. T hese differences in VMO:VL ratio may explain
why more women than men are tre a te d in th e clinic for PFPS. i.is
We a lso observed many s u b je c ts had d iffic u lty perform ing
isometric contractions a t 0 degrees. These su b jects, however, often
had their highest VMO:VL ratios a t this angle. Why this occurred is
unknown.
CHAPTER 5
DISCUSSION AND IMPLICATIONS
Discussion o f Findings
Although our fin d in g s did n ot support our h y p o th esis, w e feel
this stu d y is significant for several reasons. First, it adds to th e
literature regarding knee flexion angle and VMO strengthening.
According to our literature review, som e researchers hypothesize
th a t selective strengthening of th e VMO may be achieved
isometrically a t terminal extension (0 degrees). Still, o th e r studies
su g g e st th e VMO may be stren g th en ed isometrically a t larger angles
of knee flexion including 20, 60, and 90 degrees. Due to th e se
inconsistencies, all research pertaining to selective VMO
strengthening is beneficial inasmuch as it adds to th e small body of
knowledge in this area.
Second, our findings and much o f th e ex istin g lite r a tu r e
su g g e st th a t th e re is no single angle th a t may be universally
prescribed to selectively stren g th en the VMO (See Table 1). Our data
su g g e sts th a t m ost people have a specific angle for optimally
strengthening th e VMO.
30
31
Although many su b je cts had similar VMOiVL ratios a t all four te s t
angles, o th e r su b je c ts displayed distinctly higher values a t certain
angles. We believe this occurs as a result of differences in muscle
recruitm en t p a tte rn s b etw een individuals.
Third, t h i s stu d y i s helpful c lin ic ally because i t provides a
startin g point for developing an isom etric protocol for PFPS.
Because EMG is necessary in determining th e optimal angle for
isom etric strengthening, an EMG study m ust be perform ed on each
p atien t to determ ine which angle produces th e highest VMOiVL ratio.
Isom etrically stre n g th e n in g a t th is angle will individualize
tre a tm e n t and provide th e g re a te s t benefit for th e p atient.
Application of Practice
C onsidering th a t PFPS i s very commoni, It would benefit
clinicians to have an established protocol for this disorder. As
m entioned above, this stu d y provides a foundation for establishing a
protocol exclusive to each p a tie n t by first analyzing individual
m uscle recru itm en t p a tte rn s. Thus, individual ch a ra cte ristic s
pertaining to recruitm ent p a tte rn s m ust be considered before
issuing isom etric exercises.
Not only will th e p a tie n t benefit from
32
this approach b u t third party payors will also be more likely to
reim burse for a research-based protocol.
L im ita tio n s
The first limitation of this stu d y is in th e m easurem ent of th e
angles of knee flexion. Goniometry Is a very subjective m easurem ent
prone to human error. Norkin and White^o refer to 3 to 5 degrees of
error when measuring angles as “a c c e p ta b le .” These small
differences betw een th e actual angle and our m easured angle may
have cau sed som e discrepancies in our data.
A nother p o ssib le lim ita tio n due to human e rro r is th e
placem ent o f th e electrodes. It is virtually Impossible to place th e
electro d es in th e exact sam e sp o t on every subject. While a trained
research er should be able to properly place electrodes with great
consisten cy , su b tle variations in anatom ical landmarks betw een
su b je c ts m ake this difficult.
A th ird lim ita tio n i s th a t only fo u r an g les w e re te s te d due to
tim e co n stra in ts and th e possibility of su b je ct fatigue. This limited
our stu d y b ecau se the VMO:VL ratio may be g re a te st at an angle other
than 0, 20, 60, or 90 degrees.
33
Also, only s u b je c ts betw een th e ag es o f 21 and 37 y ears o f age
with healthy knees were used in th is study. This limits th e use of
our results. The results gained with this research may not be
applicable to populations outside th e 21 to 37 year old age bracket
or to su b jects with knee pathology.
A nother lim ita tio n i s th a t although th e te s tin g o rd e r of jo in t
angles was randomized, this did n ot m ean th e effects of fatigue and
learning w ere eliminated or minimized. It is possible th a t low third
trial values were due to fatigue. On th e o th er hand, high third trial
values may be due to learning effects. Fatigue and learning
asso ciated with th e th ree trial t e s t design may, therefore, be a
limitation of this study.
A fin a l shortcom ing o f th is stu d y w a s th e in a b ility o f som e
su b je cts to maintain an isometric contraction above th e EMG
threshold level for 3 seconds. When this occurred, th e Noraxon
Myosoft softw are recorded a se p a ra te muscle contraction each tim e
a su b je c t’s muscle activity dropped below th e threshold. As a result,
a single trial was recorded as multiple contractions and data
accuracy was compromised.
34
Suggestions for-Eutlher Research
Our stu d y w a s one a tte m p t to d ev ise a w ay to s e le c tiv e ly
recruit th e VMO during isom etric exercise using four different
angles. Although analysis revealed no significant difference in
average VMO:VL ratios betw een th e angles te s te d , several findings
noted in our study may have significant im pact on further research.
One a re a w a rra n tin g fu rth e r stu d y i s recording VMO:VL r a tio s
of subjects with PFPS. Our stu d y was limited to “normal” knees of
young, healthy su b jects with no previous history of injury, disease,
or surgery. A study of pathologic knees may reveal significant
differences betw een average VMOrVL ratios a t different angles in
comparison to healthy knees. It is possible th a t su b jects with PFPS
experience pain secondary to a significant imbalance in VMOrVL
ratios. Further research is necessary to determ ine if this is true.
A second area fo r fu rth e r rese arch involves studying VMOrVL
ratios at angles o th er th an th o se studied here. Although we believe
our study was thorough by involving angles throughout th e full range
of motion, it is possible th a t angles different than th o se in our
study could produce statistically significant results. This could be
35
achieved by testin g VMO:VL ratio a t every 5 degrees. The problem
here, however, would be fatigue from testing so m any angles a t once.
Thus, future studies may Involve g reater numbers o f su b jects to
allow each 5 degree increm ent betw een 0 and 90 d eg rees to be
m easured.
A th ird recom m endation fo r fu rth e r re se a rc h i s a stu d y sim ila r
to ours but involving only female subjects or only m ale subjects.
Through informal observation during data collection we noticed
differences in recruitm ent p attern s betw een men and women.
Because of th e s e observations and because women are anatomically
more susceptible to PFPSs, we conducted further analysis seperating
VMOiVL ratios by gender. This analysis showed th a t m en have a
g reater VMOiVL ratio than women (see Table 2). The difference in
VMOiVL ratio by gender is a possible explanation for th e lack of
significant differences in average VMOiVL ratios am ong th e angles
te ste d . We did not, however, analyze the d ata to determ ine if an
optimal angle for VMO strengthening exists for each gender.
Conclusions
T his stu d y in v e stig a te d th e p o ssib ility o f a re la tio n sh ip
36
betw een knee angle and VMO and VL activity. The findings of this
stu d y indicated th e re is no significant difference am ong th e
te s te d knee angles for th e VMOiVL atio during isom etric knee
extension. Generalizations from th e s e d ata, however, should b e made
carefully b ecause of th e characteristics of our stu d y group. Further
research is needed to in v estig ate th e possibility of significant
associations betw een VMOiVL ratios and gender, pathology, and
angles o th e r than th o se te s te d in this study.
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APPENDIX A.
Inform ed C o n s e n t Form
42
43
KNEE FLEXION AND ITS INFLUENCE
ON VMOiVL RATIOS
DURING ISOMETRIC QUADRICEPS CONTRACTION
I understand th a t this stu d y com pares th e electrical activity o f tw o
muscles during th e perform ance of exercise a t four different angles
of knee flexion and th a t knowledge gained from this research can be
used to b e tte r tr e a t individuals with chronic knee pain.
I also understand th a t:
1. p a rtic ip a tio n i n th is stu d y w ill involve one 30 m in u te
se ssio n during w hich e le c tro d e s w iII be adhered t o tw o 1
by 2 inch shaved a re a s o f my th ig h b efo re being ask ed to
perform 12 t r i a l s o f a five second ex e rc ise .
2.
I have been s e le c te d fo r th is stu d y b ecau se o f my age and
h isto ry o f no previous knee injury.
3.
i t is p o ssib le th a t I could ex p erien ce so m e m u scle so re n e s s
one to tw o days a f te r th e stu d y and a lso som e s lig h t
d isco m fo rt due to ra z o r burn.
4.
my name and my individual r e s u lts w i 11 be k ep t s t r i c t l y
confidential.
5.
a sum m ary o f th e r e s u lts w i 11 be m ade av a ila b le to m e upon
request.
I acknowledge th a t:
“I have been given an opportunity to a sk q u e stio n s regarding
th is re se a rc h stu d y , and th a t th e s e q u e stio n s have been
answ ered to my s a tis f a c tio n .”
" I n giving my co n sen t, I understand th a t I am one o f s ix ty
volunteers p a rtic ip a tin g in th is stu d y and t h a t I may w ith d ra w
44
a t any tim e during te s tin g .”
“T h e in v e s tig a to rs , Bill Allan and J e f f Rendra have my
p erm issio n to p erform th e above p ro ced u res on m e.”
“I hereby a u th o riz e th e in v e s tig a to rs to re le a s e th e
in fo rm atio n ob tain ed in th is stu d y to s c ie n tif ic lite ra tu re . I
und erstan d th a t I w ill n o t be id e n tifie d by nam e.”
“I have th e rig h t to c o n ta c t Paul Huizenga, C hair o f Human
R esearch Review C om m ittee (8 9 5 -2 4 7 2 ), o r Ja n e Toot
(8 9 5 -3 6 0 5 ), a t any tim e i f I have q u estio n s.
“I acknow ledge t h a t I have read and u n d erstan d th e above
info rm atio n , and th a t I ag ree to p a r tic ip a te in th e stu d y .”
W itness Signature
Participant Signature
Date
Date
APPENDIX B.
D ata
C ollection
45
Sheet
46
KNEE FLEXION AND ITS INFLUENCE
ON VMO:VL RATIOS
DURING ISOMETRIC QUADRICEPS CONTRACTION
Data Collection S heet
SUBJECT #
Analfi.
0
TüaL.I
V M O _________
VL
20
VMO
VL
60
VMO
VL
90
VMO
VL
_______
I n a l-2.
Trial 3
_______
_______
_______
_______
APPENDIX C.
P ro p o sal Sum m ary For
Hum an S u b je c t Review C o m m ittee
47
48
P a te llo fem o ral P ain Syndrom e (PFPS) i s th e num ber one cau se
of knee pain in many clinics and sp o rts medicine c e n te rs around th e
country. The major underlying cause of PFPS is a malalignment of
th e patellofem oral Joint. The result of th is m alalignm ent is a
laterally tracking patella causing pain for th e p a tie n t.
The v a stu s m e d ia lis obliquus (VMO) h a s been id e n tifie d a s th e
only stru c tu re with th e ability to pull th e patella medially.
Theoretically, stren g th en in g th e VMO will c o rre c t m alalignm ent th u s
relieving pain. Several exercises have been recom m ended by
researchers and th e ra p ists to stren g th en th e VMO. However, while
strengthening the VMO, th e s e exercises may also stren g th en th e
vastus lateralis (VL) to th e sam e degree. Even though th e VMO is
stren g th en ed , it may still n ot be able to pull th e patella medially
because of th e sim ultaneous strengthening o f th e VL pulling th e
patella laterally. For an exercise to be efficient in altering
malalignment and to reduce pain it is necessary to stren g th en th e
VMO independent of th e VL or a t least stren g th en it to a
significantly g reater d eg ree th an th e VL.
S ev eral a u th o rs have recom m ended an is o m e tric c o n tra c tio n o f
49
th e quadriceps to facilitate stren g th en in g of th e VMO. While som e
authors believe VMO stren g th en in g occurs a t term inal knee extension
o th ers contend th a t exercise should be perform ed a t varying degrees
of knee flexion. The problem is th a t th e re is little scientific d ata
th a t indicates th e VMO is stren g th en ed to a g re a te r d eg ree than th e
VL in any of th e se ranges of motion (ROM) during an isom etric
contraction. The purpose of th is study is to com pare th e activity of
th e VMO relative to th e activity of th e VL a t various points betw een
0 and 90 d eg rees of knee flexion during isom etric contraction. Our
hypothesis is th a t isom etric quadriceps co n tractio n s b etw een 60
and 90 d eg ree s of flexion will result in larger VMO:VL ratio s than a t
o th e r ranges of motion in healthy college age male and fem ale knees.
T estin g wi l l ta k e p lace i n th e Human P erfo rm an ce Lab lo cated
in th e Grand Valley S ta te University Fieldhouse. S u b jects for this
stu d y will consist of 60 males and fem ales ranging from 18 to 35
years of age with no history o f hip or knee problem s. The su b jects
will be se le c te d via a sam ple of convenience using physical therapy
s tu d e n ts enrolled a t Grand Valley S ta te University.
S im u ltan eo u s EMG read in g s w i 11 be ta k en o f th e VMO and VL
50
during isom etric contraction a t angles of 0, 20, 60, and 90 d eg rees
o f knee flexion. The EMG values o f th e th re e trials will th en be
averaged to establish a mean value for th e VMO and VL. T hese mean
values will th en be used to calculate a VMO:VL ratio for each o f th e
designated t e s t angles. Finally, a re p e a te d m easures analysis of
variance t e s t will be used to d eterm in e if a statistically significant
difference exists among th e VMOiVL ratios of the four angles.
C onsenting s u b je c ts w i 11 be te s te d iso m e tric a lly a t a r c s o f 0,
20, 60, and 90 degrees of knee flexion. To reduce any e ffe c ts of
fatigue o f learning, th e order in which th e angles will b e te s te d will
be selected randomly.
Once th e o rd er o f angles to be te s te d i s se le c te d , th e s u b je c t's
leg will be cleaned with an isopropyl alcohol swab and th e bellies of
th e VMO and distal VL will be shaved using a disposable razor. Each
shaved area will be
rubbed again with a clean isopropyl alcohol
swab to sanitize th e skin and maximize electrode adherence. While
th e su b je ct is se ate d , th e research er will place self-ad h eren t
surface electrodes to each o f th e d esig n ated areas. The electro d es
will then be plugged into lead wires co n n ected to a com puter with
51
MYOSOFT EMG softw are for Windows. The su b je c t’s knee will then be
positioned a t th e first randomly se lec ted angle. The padded
resistance bar of a CYBEX machine will th en be placed a t th e
anterior ankle of th e t e s t leg for resistan ce and to maintain th e knee
a t th e designated t e s t angle. When instructed, th e su b ject will
perform a maximal isom etric contraction o f th e quadriceps femoris
for five seconds against th e padded resistan c e bar. S ubjects will
perform th ree consecutive trials a t each angle with a one minute
re st betw een trials. To familiarize te s te r s with both equipm ent and
procedure, a pilot stu d y with 10 su b je cts will be perform ed. This
will help establish reliability as well as facilitate su b je c t sa fe ty .
It will be explained to each su b ject th a t so m e m uscle so ren ess will
persist one to tw o days following participation in th is study. It will
also be explained to each su b ject th a t th e y have th e right to
withdraw their participation in this experim ent a t any tim e.