Muscular and FunctionalPerformance Characteristics of

Individuals Wearing

Prophylactic Knee BracesPaul A. Borsa, MS, ATC

Scott M. Lephart, PhD, ATCFreddie H. Fu, MD

Abstract: The efficacy of prophylac-tic knee bracing has been refuted withregard to reducing the incidenceand/or severity of injuries to the kneejoint. This is thought to be a result ofthe prophylactic knee brace's ineffec-tiveness in protecting the knee jointfrom valgus loads. Furthermore, dis-crepancies exist regarding the prophy-lactic knee brace's detrimental effecton functional performance. The pur-pose of this study was to measure theeffect of the prophylactic knee brace onselected isokinetic muscular character-istics andforward sprint speed. Twentyphysically active, healthy, male collegestudents with no prior history of braceuse participated in this study. The sub-jects were randomly tested both withand without the prophylactic kneebrace worn on various performanceparameters. The dependent measures

Paul A. Borsa is a doctoral student in theExercise Physiology/Athletic TrainingProgram at the University of Pittsburgh inPittsburgh, PA 15261.Scott M. Lephart is Director of SportsMedicine/Athletic Training, an assistantprofessor in the School of Education, andan assistant professor in the School ofMedicine, Department of Orthopedics, atthe University of Pittsburgh.Freddie H. Fu is a Blue Cross/Blue Shieldof Western Pennsylvania Professor ofOrthopedic Surgery, and Team Physicianat the University of Pittsburgh.

assessed included peak torque (PT)and torque acceleration energy (TAE)at 60 and 240°/s. A 40-yard forwardsprint was selected to assess sprintspeed. A paired t-test analysis revealedmean values which were significantlylessfor PT at 60°/s (p < .05), 240°/s (p< .01), and TAE at 240°/s (p < .05)with the prophylactic knee braceapplied during knee extension. Analysisalso revealed slower times for sprintspeed (p < .01), while the subjects werewearing the prophylactic knee brace.Muscular strength (PT) and power(TAE) scores were not correlated (p >.05) with sprint speed. This study sug-gests that wearing the prophylacticknee brace may consequently inhibitmuscular and functional performanceof the athlete, but that specific popula-tion has yet to be studied.

E a pidemiological studies haverecognized that knee jointinjuries are the most common

disabling injuries in athletics.24'28Consequently, the use of prophylacticlateral knee braces in football hasincreased in an attempt to reduce theincidence and/or severity of injuries tothe knee joint. 1012,14,2731 The efficacyof such knee braces has been refutedby researchers regarding prevention oflaterally applied valgus loads that mayinduce ligamentous injuries to theknee joint. 1,2,6,21,22 The discrepanciesin the efficacy of the prophylactic ben-efits of the prophylactic knee brace

have led to inconsistencies amongclinicians recommending their use.

Inconsistencies in the available lit-erature have elicited further scrutinyregarding the effects and possibledecrements in functional performancewhile wearing the prophylactic kneebrace. The prophylactic knee bracemay inhibit leg muscle function andsprint speed, both of which are essen-tial to athletic performance.7"13'25Thus, the term "functional" as used inthis manuscript implies dynamic mus-cular activity objectively measured forcomparative analysis.The purpose of this study was to

address these discrepancies in the lit-erature by objectively measuringselected isokinetic muscular character-istics and sprint speed under thebraced and nonbraced conditions. Wehypothesized that the isokinetic mus-cular test scores would be significantlydecreased and forward sprint timeswould be significantly slower in thebraced condition, suggesting function-al inhibition.

Furthermore, there has been somedebate suggesting that sprint speed isrelated to muscular strength andpower.'5 Since these three perfor-mance parameters were measured inthis study, we also hypothesized thatstrength measured as peak torque(PT), power measured as torque accel-eration energy (TAE), and sprintspeed would be positively correlatedall during the nonbraced condition.

MethodsTwenty physically active, healthy,

male college students (age = 21.3 +

3.6yr,ht=68+2.4 in, wt= 167 ±7.2lb) with no prior history of brace usevoluntarily participated in this study.Exclusion criteria included any previ-ous knee pathology requiring surgicalintervention, anterior cruciate liga-ment deficiency, and/or patellofemoraldysfunction. Informed consentapproved by the Institutional ReviewBoard at the University of Pittsburghwere reviewed and signed by eachsubject prior to testing. The subjectacted as his own control and was test-ed on two separate sessions for bothconditions (braced versus nonbraced).

336 Volume 28 * Number 4 * 1993

The test conditions (brace or non-brace) were randomized, thus prevent-ing the occurrence of any learningeffects. The subjects attire consisted ofa t-shirt, gym shorts, and athleticshoes.Two commercially available pro-

phylactic knee braces were usedaccording to the manufacturer's speci-fications. They were selected due totheir popular use among intercolle-giate football players. The McDavidKnee Guard (MKG) (M-155;McDavid Knee Guard Inc, ClarendonHills, Ill) has a single-hinge design,while the Omni (Omni Scientific Inc,Lafayette, Ill) has a double or polyaxi-al design (Fig 1). The two prophylac-tic knee braces were randomlyassigned to subjects with 11 wearingthe MKG and 9 the Omni. The pro-phylactic knee brace was worn unilat-erally on the dominant leg for the iso-kinetic tests (Fig 2), and bilaterally fortesting sprint speed (Fig 3).

Subjects were tested with identicalprotocols on two separate days, andthe sessions were separated by 48hours to allow for proper recovery.Test protocol consisted of testing forstrength and power on the Cybex unitand sprint speed on an indoor track.

Isokinetic muscular testing wascomputed using the Cybex H isokinet-ic testing device (Lumex, Inc,Ronkonkoma, NY). Subjects complet-

Fig 1.-The McDavid Knee Guard(top) is a single-hinge design, whilethe Omni (bottom) is a double- orpoly-hinge design.

Fig 2.-During isokinetic testing,the prophylactic knee brace wasworn unilaterally.

ed a 5-minute warm-up on a Monarchstationary bicycle at a preset cadence(70 rpm) and resistance (.04 kg) rela-tive to the subject's body weight (eg,60 kg X .04 = 2.4 kp). Cybex testingwas conducted in an isolated, ther-moneutral environment. The parame-ters selected for testing included PTand TAE measured at two angularvelocities (60 and 2400/s). Peak torqueis defined and measured as the great-est torque produced during a given setof contractions, while TAE is definedand measured as the amount of workperformed in the first one eighth of asecond of torque production.5 Peaktorque is recorded as a strength mea-sure, and TAE is recorded as an anaer-obic power output measure in thisstudy.17'23 Each subject was testedusing gravity correction, and standardstabilization was employed at thechest, waist, and distal thigh.3'4 TheCybex was calibrated prior to testingof the subjects. Each subject receivedverbal instructions prior to testing, fol-lowed by five pretrial submaximalrepetitions at 600/s in order to accom-modate to the test speed. After a 30-second recovery, subjects completedfour maximal repetitions and the high-est value was recorded as PT. A 1-minute recovery was given beforecontinuing at the next test speed. Ten

submaximal repetitions were used as apretrial for testing at 2400/s in orderfor the subject to accommodate withthe faster test speed. After a 30-secondrecovery, subjects completed fourmaximal repetitions and the highestvalues were recorded as TAE and PT.

For testing sprint speed, the subjectswent through a warm-up consisting oflight jogging for 800 meters and largemuscle group flexibility exercises.Each subject familiarized himself withthe sprint distance by completing twosubmaximal trial runs. The 40-yardforward sprint was selected, due to itsreproducibility and relevance to col-lege football. The sprint was per-formed at maximal speed with themean time (seconds) of three trialsrecorded as the criterion measure. A 1-minute recovery period was givenbetween trials. Sprint times wererecorded by the same investigatorusing a hand-held stopwatch measuredto the nearest tenth of a second.

Analysis of variance (ANOVA) wasused to identify significant (p < .05)differences between the two prophy-lactic knee brace designs on the vari-ous testing parameters. The selectedisokinetic and sprint speed tests weretreated as four separate tests andpaired t-test analyses (p < .05) wereused to compare the braced and thenonbraced (control) conditions for the

I~~~ i I

Fig 3.-Frontal view of the prophy-lactic knee brace.

338 Volume 280* Number 4 * 1993

qII

---,

Table 1.-Means and Standard Deviation for Knee Extension With andWithout the Brace

Brace No brace

Knee extension (ft-lb)Peak torque 60°/s 152.9 (26.3) 158.3 (23.9)Peak torque 2400/s 51.7 (11.9) 54.4 (12.4)TAE 2400/s 29.6 (5.6) 31.2 (5.2)

40-Yard forward run (seconds) 5.3 (0.3) 5.2 (0.4)

selected measures. Also, PearsonProduct Moment Correlations werecomputed to determine significant (p <.05) correlations between strength (PTat 60 and 240°/s), anaerobic power(TAE) at 240°/s, and sprint speed (40-yard forward sprint).

ResultsThere were no statistically signifi-

cant (p < .05) differences between thetwo designs on the various testingparameters (F(1,18) > 3.73, p > .07).Therefore, the data were pooled, andfurther analyses were performed with-out regard to brace design.

Isokinetic strength and powerscores were significantly lower whilewearing the brace during knee exten-sion for PT at 60°/s (t(19) = 1.80, p =.04) and 2400/s (t(19) = 2.66, p =.008), and TAE at 2400/s (t(19) = 2.19,p = .02; Table 1). Subjects ran faster(40-yard forward sprint) when thebraces were not worn (t(19) = 3.05, p= .003; Table 1). Correlations betweenstrength (PT at 60 and 240°/s), andsprint speed were low and not signifi-cant (p < .05) (PT at 60°/s and sprintspeed (r = .21), and PT at 240°/s andsprint speed (r = .11)). Also, correla-tions between power and sprint speedwere low and not significant (p < .05)(TAE (240°/s) and sprint speed (r=.37)).

DiscussionThe original premise for wearing

prophylactic knee braces was to pre-vent or reduce the incidence and/orseverity of knee joint injuries.Retrospectively, researchers beganconducting longitudinal studies com-paring injury rates before and after theprophylactic knee brace was beingused. Subsequently, the results ofthese long-term epidemiological stud-

ies suggest that prophylactic kneebracing does not reduce the incidenceand/or severity of injuries to the kneejoint of college football players,specifically injuries to the medial col-lateral ligament, anterior cruciate liga-ment, and medial meniscus.10'12'14,27-31This has led other investiga-tors1' 2'6'2122 to conduct biomechanicalin vivo and in vitro studies designed tomeasure brace function under simulat-ed conditions. Paulos et al6'21"22 andBaker et al" 2 have pioneered thesestudies evaluating the static stabilizingqualities of the prophylactic kneebrace using both cadaveric and surro-gate knee models. They concludedthat the prophylactic knee brace doesnot prevent valgus loading of the kneejoint from laterally applied contactblows. Other investigators26'32 specu-lated that the prophylactic knee braceis not designed and constructed suffi-ciently to transfer valgus loads awayfrom the knee joint (Fig 4).

In addition to the prophylactic kneebrace's questionable efficacies, manyresearchers are unclear as to the effectthe prophylactic knee brace has onvarious performance parameters. Todate, the degree to which the prophy-lactic knee brace inhibits functionalperformance is inconsistent in the lit-erature and has resulted in consider-able controversy.7"13'23 Therefore, ifthe prophylactic knee brace fails toperform as initially prescribed andalso inhibits athletic performance, thenit should not be recommended for ath-letic use.

This study revealed that prophylac-tic knee braces do indeed inhibit spe-cific performance parameters in sub-jects unaccustomed to wearing pro-phylactic knee braces, and this inhibi-tion may result in subsequent decre-ments in athletic performance. In our

study, generation of PT and TAE dur-ing knee extension at 60 and 2400/swas found to be significantly inhibitedwhile wearing the prophylactic kneebrace, as was forward sprint speed.Others reported similar findings; high-er PT values at four angular velocities(30, 90, 180, and 300°/s) without thebrace'3 and forward sprint speeddeficits when the prophylactic kneebrace was worn.7'25 These findings areinconsistent with reports by Hansen"and Clover (unpublished research,Riverside, Calif, 1984) suggesting thatprophylactic knee brace's have noeffect on isokinetic muscular function.Houston and Goemans'3 reported

significant differences in maximalanaerobic power output on theMargaria-Kalamen (M-K) step test,suggesting that the knee braces mayhave an inhibitory or "dampening"effect on peak anaerobic power out-put. This finding supports our study inthat peak anaerobic power outputdecreased significantly when thebraces were worn. Anaerobic poweroutput was measured in our studyusing the TAE value recorded at240°/s on the Cybex (Table 1). TAE,as defined earlier in the text, is a mea-sure of instantaneous power output

Fig 4.-The prophylactic knee braceis designed to: (a) absorb the lateralblow, (b) redirect the forces awayfrom the knee joint, and (c) preventopening of the medial knee joint.

340 Volume 280 Number 4.* 1993

and is done under completely anaero-

bic conditions.16'20Lephart et al17 reported TAE to cor-

relate well with anaerobic power (M-Kstep test; r = .73), although furtherinvestigations should substantiate thesefindings. Similarly, Kalamen15 reporteda high correlation (r = .97) between thetime of running the 50-yard dash andthe M-K step test. This suggests thatthe 50-yard forward sprint may be usedas a valid measure of anaerobic power.

Although our study used the 40-yardforward sprint, we feel this distance iscomparable to the distance used byKalamen,'5 and may also be used as a

valid measure of anaerobic power.

Peak torque and TAE during kneeextension is a reflection of the quadri-ceps maximal tension generatingcapacity4 and any deficits in thequadriceps capacity to generate ten-sion should affect the potential for for-ward sprint speed. The relationshipbetween muscular strength and sprintspeed has not been extensively investi-gated and strong relationships are notwidely reported.5 8'18 The hip flexorsare most active during sprinting;apparently because they are closelylinked to the knee extensors in pro-

pelling the body forward.'9 This sug-

gests that the biarticular knee exten-sors/hip flexors may provide the nec-

essary impetus for sprint speed due totheir high activity during sprint run-

ning. According to our study, thereappears to be little relationshipbetween quadriceps strength/powerand sprint speed. This may be due inpart to the small subject size. Overall,when comparing muscular strengthand sprint speed, few have revealedconsistencies between muscular andfunctional inhibition indicating thenecessity for further investigation.

Since wearing the prophylactic kneebrace appears to inhibit isokinetic mus-

cular strength parameters and sprintspeed, we speculate that the brace mayinhibit some other functional perfor-mance parameters. Studies identifyingthe effects of prophylactic knee brac-ing on agility are limited7'25 and resultsare not consistent within the literature.Again, further studies are necessary.

In addition to the results from the

muscular function inhibition studies,some researchers have suggested thatother factors may affect sprint speed.Van Horn et a132 reported that whenprophylactic knee braces were worn,

significant differences in gait patternswere observed. These alterations were

speculated to be some form of com-

pensatory motions to counter theeffects of the brace. This may haveimplications for future improvementsin brace design and placement.26'33

Prophylactic knee braces have beenunder investigation for some time.Most researchers have found the pro-

phylactic knee brace to be ineffectivein preventing injury to the knee joint,yet many clinicians and athletes con-

tinue to recommend and use the brace.The results of this study reveal that theprophylactic knee brace does indeedinhibit selected isokinetic muscularcharacteristics and forward sprintspeed in subjects who are unaccus-

tomed to wearing prophylactic kneebraces, and both of these factors may

ultimately inhibit athletic perfor-mance. Furthermore, the differencebetween the two mean sprint timesappears to be small for this study(Table 1), yet deficits as small as one

tenth of a second may be practicallysignificant for athletes who demandmaximal speed. Therefore, the use ofprophylactic knee braces for athleteswho require maximal muscular func-tion and sprint speed should be scruti-nized with regards to the limitedreported prophylactic benefits of suchbraces.

This study used subjects unfamiliarwith prophylactic knee brace use, thusproviding a novel motor task for thesubjects. Conversely, athletes who are

accustomed to wearing prophylacticknee braces have conditioned an

ingrained (habituated) motor task rela-tive to their performance. The noveltyof the task for the subjects in thisstudy may affect the external validityof the study. Therefore, any significanteffects demonstrated by the subjects inthis study may be due to the unfamil-iarity of the tasks and will make gen-

eralizability to the athletic populationdifficult. For future research, we rec-

ommend using athletes who are accus-

tomed (habituated) to wearing the pro-phylactic knee brace in order toincrease the generalizability of our

results to a more habituated athleticpopulation. We also recommendinvestigating further the relationshipbetween muscular strength/power andsprint speed, as well as investigatingthe braces' effects on other perfor-mance variables, such as propriocep-tion, metabolism, kinetics, and kine-matic function.

AcknowledgmentWe would like to express our sin-

cere gratitude to Dr. Carol Baker forher statistical and design assistance.

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344 Volume 28 * Number 4 * 1993