Isokineticsand Exercise

ScienceELSEVIER Isokinetics and Exercise Science 6 (1996) 133-138

The effects of patellar bracing on quadriceps EMG activityduring isokinetic exercise

Larry K Gulling, Scott M. Lephart*, David A. Stone, James J. Irrgang,Danny M. Pincivero

Neuromuscular Researr:h Laboratory, Sports Medicine Program, 104 Trees Hall, University of Pittsburgh, Pittsburgh, PA 15261, USA

Abstract

Patellofemoral pain syndrome is a prevalent ailment experienced by a number of individuals participating in regular physicalactivity. Little information is available concerning the effects of patellofemoral bracing on the function of the extensormechanism in patellofemoral malalignment patients. The purpose of this study was to examine the effects of patellar bracingon the extensor mechanism in relation to isokinetic exercise. Sixteen subjects exhibiting patellofemoral pain symptoms weretested on an isokinetic dynamometer with and without a patellofemoral brace. The testing procedure involved three maximalconcentric/eccentric quadriceps contractions at an angular velocity of 1800/s. Electromyographic (EMG) activity of the VastillSmedialis obliqus (VMO) and the vastus lateralis (VL) were recorded during testing. Integrated EMG activity (IEMG) wasanalyzed by a three-way ANOV A with repeated measures (P < 0.05). The results indicated that the application of the patell;arbrace resulted in a significantly smaller IEMG signal than during the non-braced condition in both the VMO and VL duringboth concentric and eccentric contractions (P < 0.05). The IEMG signal of the VMO was found to be significantly greaterthan the VL regardless of test or brace condition (P < 0.05). Moreover, the IEMG signal was also found to be significantlygreater during the concentric contractions than the eccentric contractions during all testing conditions (P < 0.05). The clinicalimplication from this study suggests that muscle activation of the VMO and VL were reduced with the use of the brace. Thlistype of bracing may provide mechanical support to the patellofemoral joint as evidenced by the reduction in quadricelpsactivation during isokinetic knee extension exercise. Copyright @ 1996 Elsevier Science Ireland Ltd.

Keywords: Patella; Brace; Electromyography; Isokinetic

1. Introduction and, more specifically, as a cause of patellofemoralpain. Malalignment, in its simplest sense, may beconsidered abnormal tracking of the patella in thetrochlear groove during functional activities.Patellofemoral malalignment may be a resulltof an imbalance of the extensor mechanism[2,3,12-14,16-18], specifically the vastus media]lisoblique (VMO) and the vastus lateralis (VL), abnor-mal anatomical architecture [3,12,16-18], increaseda-angle [2,12,15,16], genu valgus, genu recurvatum,pronated feet, femoral neck anteversion, hypermobilepatella [14-16], patella alta [11,14-16], abnormaliti,esin the patellar retinacuIar restraints [3,17,18], ilio-tibialband syndrome and VMO insufficiency [2,12,14-115].Correct biomechanical alignment of the extenslormechanism has therefore been suggested to be partly

Anterior knee pain is one of the most commonknee problems experienced by recreational and eliteathletes. Although there is no formal clinical defini-tion of patellofemoral pain syndrome, PFPS, it isoften characterized by a diffuse, poorly localized painthat arises from abnormal tracking of the patella [7].It is currently believed that an underlying etiology ofPFPS is malalignment of the patellofemoral joint,resulting from pathological conditions producing an-terior knee pain [17]. Patellar malalignment is wellrecognized as a potential cause of chondromalacia

*Corresponding author. Tel.6487092.

+

1 412 6488261; fax: + 1 412

0959-3020/96/$15.00 Copyright @ 1996 Elsevier Science Ireland Ltd. All rights reservedPIIS0959-3020(96)00158-0

134 L.K GuJJinget aJ. / Isokinetics and Exercise Science 6 (J996) 133-138

strated symptoms indicative of patellofemoral painsyndrome and one or more abnormal values reportedfrom a Merchant-view roentgenogram. Subjects wereevaluated by one orthopedic physician to screen forpatellar facet tenderness. All subjects demonstratedfull knee range of motion (approximately 135-140°),no pain during a maximal manual quadriceps strengthtest and reported no previous lower extremity strengthtraining 3-4 months prior to testing. All subjects werealso full weight bearing and reported minimal painduring light daily activities. Each subject was evalu-ated for isokinetic strength with the application of thepatellar knee brace and without brace application.The order of the two testing procedures were ran-domly assigned.

2.1. lnstmmentation

Subjects were tested on the Kinetic CommunicatorII (Kin-Com) isokinetic dynamometer (Chattex Corp,Chattanooga, TN). The patella orthosis chosen forpatellar bracing was the UlOO4-patellar stabilizer(Sports Supports Inc., lIVing, TX) which consists of aneoprene sleeve with a cut out for the patella and afelt horseshoe buttress that surrounds the patellaalong its superior border. Cleartrace LT disposableadhesive gel silver/silver-chloride surface electrodes(Medtronic Andover Medical, Haverhill, Mas-sachusetts) were used to record myoelectrical activityof the VMO and VL.

~

dependent upon a properly functioning VMO [16].Conservative treatment of patellofemoral pain syn-

drome is perhaps the most commonly used approachfor dealing with this ailment, as opposed to surgicalintervention. Such treatment options have includedhamstring flexibility exercises, quadriceps strengthen-ing (specifically the VMO), aquatic exercises, salicy-lates, non-steroidal anti-inflammatory medications,analgesics, arch orthosis, immobilization of the patellaand patellar bracing [1,10].

The quadriceps extensor mechanism has been stud-ied from several viewpoints, usually torque, muscleforce and biomechanics, electromyography (EMG)and radiography. With respect to biomechanics, thepatella functions in a variety of roles. The patella'sprimary function is to increase the extensor mecha-nism's moment arm and therefore increases its effi-ciency and mechanical advantage during knee exten-sion [6]. Secondly, it functions to decrease the frictionand shearing of the patellar tendon, allowing it towithstand high repetitive loads. Likewise, the patellafunctions to centralize the divergent heads of theextensor mechanism by neutralizing the four differentvectors of the quadriceps muscles [5] (Fig. 1).

The ability to alter function of the extensor mecha-nism by the use of patellar bracing has been sug-gested to alleviate symptoms of patellofemoral painsyndrome [15]. Advocated functions of patella bracesinclude improvement of tracking, dispersal of force,maintenance of patellar alignment, prevention ofstraining the medial retinaculum and prevention ofsubluxation and dislocation [2,11,13,15]. Although,Cherf [2] suggested that bracing has often been usedin conservative treatment of patellar instability, itsphysiological function has not received much investi-gation. The purpose of this study was to examine theeffects of patellar bracing on EMG activity of thevastus lateralis and vastus medialis muscles duringisokinetic knee exercise.

2.2. /sokinetic assessment

2. Materials and methods

Sixteen athletically active individuals with a meanage of 24.5 years (range, 18-38 years) volunteered toparticipate in this study. All the subjects entered intothis study were concurrently participating in physicaltherapy in an out-patient clinical setting. After sub-jects provided written informed consent approved bythe Biomedical Institutional Review Board at theUniversity of Pittsburgh, demographic data includingpast history of knee pathology, knee surgery andsymptoms of patellofemoral pain was obtained. Crite-ria for inclusion in this study were point tendernessupon palpation of the medial patellar facets, no his-tory of knee surgery or traumatic knee ligamentousinjury, no isokinetic training experience, demon-

iI

~.

Each subject was positioned in an upright, comfort-able seated position on the Kin-Com Dynamometerchair. The back support was adjusted, allowing thesubject's thigh to be supported as well as allowing theknee to be tested to move beyond 900 of knee flexion.The anatomical axis of the knee being tested wasaligned with the mechanical axis of the dynamometer.Waist and thigh straps were used to stabilize thesubject during the testing session. The tibial forceplate on the input arm was positioned 2 inch abovethe superior border of the medial malleolus.

Start and stop angles were programmed into theKin-Com's computer after the subject was positioned.Anatomical zero was determined after the subjectperformed a full active knee extension without thetibial force plate attached. The tibial force plate wasthen attached to the fully extended leg. The Kin-Corn'sgoniometer was calibrated to read thi~ position asanatomical zero. The subject's leg was then loweredto 00 as read by the Kin-Corn's goniometer and wasused as the starting position for eccentric quadricepscontraction and stopping position for concentricquadriceps contraction. The lower leg was then moved

oli

DeK(Cbfila

-

L.K Gulling et al. / lsokinetics and Exercise Science 6 (1996) 133-138 135

position as read by the Kin-Corn's goniome-and this was used as the starting position for

quadriceps contraction and stopping posi-for eccentric quadriceps contraction. Each sub-was .required to generate an initial thresholdof 25 N against the input arm to activate the

Kin-Corn's Servo mechanism. Gravity correction wasperformed for each subject with the knee in a positionof full extension. With the subject in a relaxed posi-tion, the knee was then moved passively into flexionas the Kin-Com automatically adjusted for gravity.

Subjects were familiarized with the procedures thatwere used to activate the Kin-Corn's input arm foralternating concentric and eccentric quadriceps con-traction, and likewise, to the standardized verbal com-mands used during the testing session. The verbalcommands were consistent with each subject and alsoduring all the test trials. Each subject was given foursubmaximal quadriceps contractions for familiariza-tion prior to testing. A rest period was provided toeach subject prior to the test procedure. The restperiod varied accordingly for each subjects' subjectivefeelings of full quadriceps recovery following thepractice trials. The concentric contractions were per-formed first from a starting angle of 90° of kneeflexion. Once the knee reached terminal extensionCOO), the eccentric contractions were then performed.The testing session consisted of three maximal, alter-nating concentric/eccentric quadriceps contractionswith and without patellofemoral brace application.The testing procedure for data collection followed thesame format used in the practice session with theorder of conditions randomized. Subjects were en-couraged to exert a maximum effort during eachcontraction condition.

ject's test session. Raw EMG signals were collected ata sampling frequency of 1000 Hz, pre-amplified with a1 000000: 1 gain pre-amplifier and processed throughanalog to digital conversion. The full wave rectifiedEMG activity (mV) was integrated (IEMG) and storedon an IBM microprocessor and were analyzed oruyover the 10-350 arc of motion. This was done forthree reasons: (1) to exclude from analysis the myo-electrical activity needed to initiate movement of tilelimb and to accelerate the limb to the target angularvelocity; (2) the potential for subluxation and disloc:a-tion occur at this range of motion of knee flexion; alild(3) to maintain a coIilSistent value for range of motionin order to compare the IEMG activity between t]i1eexperimental conditions. A three-way ANDV A withrepeated measures was used to detect significant dif-ferences between the following three experimenl:alconditions: (1) brace application (with vs. without); (2)contraction type (concentric vs. eccentric); and (3)muscle (VMD vs. VL). A pre-set alpha level of P <0.05 was used for statistical significance. (Fig. 1)

3. Results

The results from this study demonstrated significantmain effects for IEMG activity for each of the thrl~econditions but there were no two-way or three-w;~yinteractions that were found to be significant. 'nlemeans and standard deviations for the three condi-tions are presented in Table 1. The overall IEMGactivity for the VMO was significantly greater th!lfithe VL (F1,IS = 17.55, P < 0.05), the concentric m1J~-cle contraction was significantly greater than the ec-centric muscle contraction (F1,IS = 18.18, P < 0.05)and the non-braced condition was significantly greatl~rthan the braced condition (F 1,15 = 4.86, P < 0.05).

2.3. Electromyographic assessment4. Discussion

The EMG electrode placement sites were identifiedand prepared in the following manner. The subject'sVMO and VL of the sampled limb were identifiedwhile performing a maximal isometric quadricepsmuscle contraction. The centers of the VMO and VLmuscle bellies were prepared by shaving the area andscrubbing with isopropyl alcohol and sterile gauze toreduce myoelectrical impedance. The centers of theelectrodes were placed 3.0 cm apart and secured withclear tape and an elastic bandage and were placedalong the longitudinal axis of the muscle fibers (Fig.2). The two ground electrodes were positioned overthe bony prominence of the medial and lateral malle-oli, with the skin surface prepared in the same man-ner as the electrodes over the VMO and VL. TheKCjEMG processing system (Chattex Corporation,Chattanooga, TN) was calibrated as outlined by themanufacturer's operations manual prior to each sub-

...

rsased'as

:psric'ed

The major findings from the present study indicatethat the IEMG of the knee extensor muscles duringisokinetic exercise was significantly lower followingthe application of the patellar brace. In addition, itwas also found that the IEMG for the VMO wassignificantly greater than the VL during the testingprocedure. The results from this study appear todemonstrate that patellar bracing may affect neuro-muscular activation of the quadricep muscles duringisokinetic knee extension. The decrease of overallIEMG activity following application of the patellarbrace may contribute to a reduction in symptoms Ibyreducing abnormal patellar tracking induced by astronger muscle contraction.

Since IEMG activity was recorded and analyzedthrough a limited range of motion in this study(10- 35°), definitive conclusion regarding the effects of

136 L.K Gulling et al. / /sokinetics and Exercise Science 6 (1996) /33-138

Table 1EMG activity (mY) of the VMO and VL by exercise condition (concentric and eccentric) and brace condition

~~II~~~~\~~~Fig.

2. Isokinetic and EMG preparation for the VMO and VLmuscles.Fig. 1. Dynamic pull of the VMO and VL muscles of the quadri-ceps mechanism. (Reprinted with permission from Ciccotti MG,Kerlan RK, Perry J, Pink M. An Electromyographic Analysis of theKnee During Functional Activities. II. The Anterior Cruciate Liga-ment-deficient and -reconstructed Profiles. Am J Sport Med.1994;22(5):651-658.)

Previous investigators have concluded that the ap-plication of a dynamic patellar brace with a lateralbuttress was beneficial in alleviating symptoms inpatients with patella subluxation [15]. Although thepresent study did not include a subjective evaluationof brace application, the findings reported appear tobe consistent with other studies. Palumbo [15] re-ported a 93% alleviation of symptoms in the patientstreated with a dynamic patellar brace with a lateralbuttress

and concluded that the brace was beneficialin conjunction with a strict VMO rehabilitation pro-gram in those patients with patella subluxation. Simi-larly, Levine [11] reported good results with a patellartendon brace he developed which encircles the leg

Sl

id

patellar bracing on patella contact area with the fe-mur are not warranted. The patella contacts the artic-ular surface of the trochlea at 20-300 of knee flexion.Patellofemoral contact is continuous from the medialto the lateral facets and begins distally on the patellaand progresses to the proximal pole by 900 of flexion.Flexion past 900 induces contact of the odd facet. Asthe contact zone moves proximal to the patella, thecontact area increases. However, increased contactarea helps to distribute and disperse this force [2].

t

~

Braced Non-braced

Braced

VMObVLb

823.44:t 314.18577.31 :t 205

874.88 :I: 354.77574.75:1: 228.97

539.56:t 279.12372 :t 144.36

660.12:t 409.86397.75:t 147.15

VMO. vastus medialis oblique; VL, vastus lateralis.a EMG activity greater during concentric contraction than eccentric contraction under each condition (P < 0.05).b VMO EMG activity greater than VL under each condition (P < 0.05).

i

L.K Gullinget aJ. / Isokinetics and Exercise Science 6 (1996) 133-1381.37

of the quadricep muscles were found during the con-centric contraction as compared to the eccentric con-traction. These findings appears to be in agreementwith others [9,19]. Westing et al. [19] found signifi-cantly lower EMG activity (7-31%) under eccentJricloading of the quadriceps as compared to velocitymatched concentric loading. Likewise, Komi et al. 1:9]reported that EMG activity remained at very lowlevels under eccentric loading of the quadriceps mus-cles as compared to higher activity during concentJciccontractions. More recently, however, Ghori et al. 1:4]reported no significant differences in EMG activityfor the quadriceps between concentric and eccentJricisokinetic exercise performed at 300/s and subs,e-quently concluded that there is no fixed relationsb,ipbetween EMG activity of the VL and quadricepstorque during maximal concentric and eccentric con-tractions. It has been established that under concen-tric contractions, the generated force is the result ofthe contractile elements of the muscle whereas tJileelastic and non-contractile tissues of muscle increasetheir role in force production during eccentric move-ments [8]. The possibility of a relationship betwel:neccentric muscle activation and patellofemoral pa.inand/or bracing, however, is beyond the scope of tJilepresent study and therefore warrants further investi-gation.

5. Summary

The clinical implication from this study is thatneuromuscular activation of the quadriceps musclesappear to be lowered following the application of apatellar brace with a lateral buttress during isokinelJCknee extension exercise. However, it is still not yetknown if this decreased activation contributes to analteration in patellofemoral joint biomechanics andpatellar alignment. Future research should focus onthe relationship between objective measures of neuro-muscular and articular mechanics and function withsubjective feelings of comfort that may be associatc~dwith brace application. If such a positive relationshipdoes exist, patellar bracing may allow the inclusion ofisotonic and isokinetic exercises in a rehabilitationprogram and therefore, allow an earlier resumption ofrecreational and athletic activities. The present studyappears to suggest that isokinetic knee extension e:x-ercise may be affected following the application oj' apatellar brace in patellofemoral pain patients that isindependent of muscle (VMO or VL) and mode ofcontraction (concentric or eccentric),

t

References

below the patella and suggested that the brace mayalter the mechanics of the patella via repositioning.Lysholm [13) proposed that a patella brace with alateral buttress may be able to compensate for amalalignment of the patellofemoral joint. The resultsfrom the present study may offer a possible explana-tion that partly accounts for the successful resultsreported by Palumbo [15), Levine [11] and Lysholm[13]. Decreases in neuromuscular activation observedfrom the present study may result in the reduction ofmuscular tension thereby reducing pain causingpatellofemoral joint forces. Alternatively, the mechan-ical support provided by the lateral buttress duringisolated knee extension exercise may provide a 'guide'for patellar tracking which may reduce the need forquadriceps activation. However, the present study didnot attempt to prove the possible relation betweenthe mechanical action of the patella following braceapplication and quadriceps activation.

The present study demonstrated that activation ofthe VMO was greater than the VL during both modesof contraction (concentric and eccentric). This findingappears to be in conflict with that of Voight et al. [18)who evaluated the reflex response times of the VMOand VL to a patellar tendon tap using electromyogra-phy in normal subjects and also subjects with extensormechanism dysfunction. It was reported that the VLfired significantly faster than the VMO in patientswith extensor mechanism dysfunction, and thereforesuggested that patients with extensor mechanism dys-function may be demonstrating a neurophysiologicalmotor control imbalance. It is important to note thatsubjects in the present study were tested as they wereidentified, and therefore, were not discriminated onprevious rehabilitation protocols. Since VMOstrengthening has been widely accepted as an integralpart of the treatment protocol, the increase in VMOIEMG activity observed in the present study mayhave partly been a function of previous rehabilitation.Sczepanski et al. [17] investigated the effects of arc ofmotion, angular velocity, and contraction type on theVMO:VL Absolute Averaged EMG (AAEMG)ratio. The results of their study indicated that theVMO:VL AAEMG ratio was affected by angularvelocity of the isokinetic exercise, and therefore, sug-gested that isokinetic exercise may be an effectivemeans of altering the muscular imbalance betweenthe VMO and VL in patients with patellofemoralmalalignment [12). Future considerations should bedirected towards the effect of isokinetic strengtheningor other forms of rehabilitation exercises on changesin neuromuscular activation patterns of the quadri-ceps muscles.

Although the present study did not investigateisokinetic force differences between the differentmodes of contraction, a significantly greater activation

[1] Arnheim DD. Modem Principles of Athletic Training. St.Louis: Times Mirror/Mosby College Publishing, 1989.

138 L.K Gulling et al. I /sokinetics and Exercise Science 6 (/996) 133-138

..(

~(

malalignement: a clinical review and preliminary report. JManip Physiol Ther 1991;14:428-435.

[13] Lysholm J, Nordin M, Ekstrand J, Gillquist J. The effects of apatella brace on performance in a knee extension strengthtest in patients with patellar pain. Am J Sport Med1984;12:110-112.

[14] MacIntyre D, Robertson G. Quadriceps muscle activity inwomen runners with and without patellofemoral pain syn-drome. Arch Phys Med Rehab 1992;73:10-14.

[15] Palumbo PM. Dynamic patellar brace: a new orthosis in themanagement of patellofemoral disorders. Am J Sport Med1981;9:45-49.

[16] Reynolds 1., Levin T, Medeiros J, Adler N, Hallum A. EMGactivity of the vastus medialis oblique and the vastus lateralisand their role in patellar alignment. Am J Phys Med1983;62:61-70.

[17] Sczepanski T, Gross M, Duncan P, Chandler J. Effect ofcontraction type, angular velocity and arc of motion onVMO:VL EMG ratio. J Sport Phys Ther 1991;14:256-262.

[18] Voight M, Wieder D. Comparative reflex response times ofvastus medialis obliqus and vastus lateralis in normal subjectsand subjects with extensor mechanism dysfunction. Am JSport Med 1991;19:131-137.

[19] Westing SH, Gresswell AG, Thorstensson A Muscle activa-tion during maximal voluntary eccentric and concentric kneeextension. Eur J Appl PhysioI1991;62:104-108.

[2] Cherf J, Paulos L. Bracing for patellar instability. Clin SportMed 1990;9:813-821.

[3] Fulkerson J, Shea K. Current concepts review: disorders ofpatellofemoral alignment. J Bone Joint Surg 1990;72A:1424-1429.

[4] Ghori GMU, Donne B, Luckwill RG. Relationship betweentorque and EMG activity of a knee extensor muscle duringisokinetic concentric and eccentric actions. J ElectromyogrKinesioI1995;5(2):109-115.

[5] Hehne HJ. Biomechanics of the patellofemoral joint and itsclinical relevance. Clin Orthop Rei Res 1990;52A:73-85.

[6] Ireland ML. Patellofemoral disorders in runners and bicyclist.Ann Sport Med 1987;3:77-84.

[7] Jacobson K, FIandry F. Diagnosis of anterior knee pain. ClinSport Med 1989;8:179-195.

[8] Kellis E, Baltzopoulos V. Isokinetic eccentric exercise. SportsMed 1995;1~3):202-222.

[9] Komi PV, Kaneko M, Aura O. EMG activity of the legextensor muscles with special reference to mechanical effi-ciency in concentric and eccentric exercise. Int J Sports Med1987;8:22-29.

[10] Kulund DN. The Injured Athlete. Philadelphia, PA: JB Lip-pincott Co., 1982.

[11] Levine J. A new grace for chondromalacia patella andkindered conditions. Am J Sport Med 1978;6:137-140.

[12] Linsheng W. Evaluation and manipulative therapy of patellar

.,

I,