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Relationship of Knee Extensor Strength andHopping ~ e s t erformance in the ~ssessmentofLower Extremity FunctionHi la ry 6 . Greenberger, MS, PT, OCS'Ma r k V. Paterno, MS, PT2

sokinetic strength testing hasbeen used as a primary assess-ment tool to determine a pa-tient's strength, ability toprogress to advanced activities,

and ability to return to a maximumlevel of function (1,24). This type oftraining and testing is referred to asopen kinetic chain exercise, wherethe muscle acts in isolation to per-form a task, accomplished throughincorporation of a combination ofseveral joints united successfullywhere the end segment is not fixed(11.23). This method was previouslyviewed as the optimal rehabilitationapproach for various lower extremityinjuries as rehabilitation protocolsfrom the late 1970s and early 1980semphasized open kinetic chain exer-cise throughout treatment. Successwith open kinetic chain isokineticstrength tests was used as an indica-tion to progress to higher levels ofactivity (5,6,24).

Recently, literature has suggestedthat isolated muscle testing does notgive enough information on a pa-tient's functional ability, especially inthe sports arena (11 l a) . Addition-ally, training only in an open kineticchain cannot sufficiently prepare thepatient to return to a dynamic func-tional level ( l8 ,2 l) . Hence, closedkinetic chain testing and rehabilita-tion were developed. Closed kineticchain exercise of the lower extremityis a dynamic incorporation of several

Traditionally, open kinetic chain rehabilitat ion and evaluation have been used as the primarytoo l to assess a patient's strength and readiness to progress to a higher functional level. Morerecently, closed kinet ic chain activities have been developed and well documented as an alternatemeans to prepare and evaluate a patient's abi lity to return to a higher functional level. However, adearth in recent literature comparing the correlation between an open kinetic chain isokineticstrength test and performance on a functional performance test exists. Therefore, the purpose of thisstudy was to examine the relationship behveen a knee extensor strength and functional performancetest, specifically the one-legged hop for distance. Twenty subjects (X = 20.7 years), w ith no priorhistory of lower extremity injury, participated in the study consisting of isokinetic evaluation of thequadriceps muscle using a Kinetic Communicator and a one-legged hop for distance. lsokinetictesting was performed at 240Ysec. All tests were performed on the dominant and nondominantlimbs. Pearson product moment corre lation coefficients for peak to qu e and distance hopped were.78 for the dominant leg and .65 for the nondominant leg (p < .05).These results support the beliefthat isokinetic strength does not correlate strongly w ith functional tasks.Key Words: functional testing, muscle strength, knee' Assistant Professor, lthaca College, Department of Physical Therapy, Ithaca, NY 14850Staff Physical Therapist, Cincinnati Sports Medicine and Orthopaedic Center, Cincinnati, OH. Mr. Patemowas a physical therapy student at lthaca College at the time this study was conducted.

muscles necessary to accomplish afunctional task through the use of acombination of several joints succes-sively when the end segment is fixed(11,23).

Literature suggests that rehabili-tation in a closed kinetic chain is asafer and more functional way totreat and evaluate lower extremityinjuries (4,lO,23,29). This suggestionis particularly true in the rehabilita-tion of patients following anteriorcruciate ligament injury as the forcesproduced with closed kinetic chainactivities result in less anterior tibia1translation than open kinetic chainactivities (10,23,30,31). Several au-thors have agreed that lower extrem-

ity functional performance tests per-formed in a closed kinetic chain arean extremely valuable evaluative tool(1,4,8,17,18,20,22,26). Since func-tional performance tests attempt toreproduce an environment withforces experienced daily, they areconsidered more functional andshould be included in the assessmentof a patient's readiness to return totheir previous level of function (2-4,8,9,16,22,25-27). Specifically, theone-legged hop for distance simulatesa task frequently needed in varioussports and functional activities. Infact, the International Knee Docu-mentation Committee (IDKC) hasincorporated a functional one-leggedVolume 22 Number 5 November 1995 JOSPT

Journal of Orthopaedic & Sports Physical TherapOfficial Publication of the Orthopaedic and Sports Physical Therapy Sections of the American Physical Therapy Associa


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- - R E S E A R C H S T U D Y

Male ( N = 7) Female ( N = 13) Combined ( N = 20 )Subject - - -X SD X SD X SDAge (years) 21.9 2.9 20.1 0.8 20.7 1.9Height (cm) 180.7 7.1 166.7 6.0 171.7 9.3Weight (kg) 75.6 9.7 59.7 5.7 65.1 10.6

TABLE. Subject characteristics.hop into its knee ligament evaluationform as its only determinant of a pa-tient's functional level, further fortify-ing the belief that horizontal h o pping is an aspect of function (7).

Recently, various functional per-formance tests have been developedto better assess the patient's ability toreturn to a higher level of function.Functional performance tests such asshuttle runs (10,19,20), carioca runs(10,19,20), and single-leg hops (1,8)have been studied to determine theirusefulness in the evaluation of pa-tients with lower extremity dysfunc-tion. Specifically, these tests were de-signed to evaluate the patient's dy-namic functional level, taking intoaccount strength, endurance, power,and coordination (21 .

Isokinetic testing in an openchain has been used to evaluatestrength. However, studies have indi-cated a lack of strong correlation be-tween involved extremity physicalcharacteristics, such as the results ofresisted strength tests and func-tional tests. This weak correlation

There was a significantcorrelation betweendistance hopped and

knee extensor strength.has been shown in patients withACMeficient knees (18) as well aswith patients following total hip re-placement (28).

Based on this review of the litera-ture, it might be surmised that isoki-netic strength may not necessarilyguarantee patient success with closed

kinetic chain functional performancetests. Therefore, the purpose of thisstudy was to determine the relation-ship between knee extensor strengthof the quadriceps and performanceon a one-legged hop for distance teston subjects with no prior history ofknee injury.

METHODSSubjects

Twenty subjects (seven males and13 females) from a college commu-nity, representing a sample of conve-nience, served as participants for thisstudy. Subject characteristics are out-lined in the Table. To be included inthe study, subjects had to meet thefollowing criteria: I) no prior historyof unresolved pain, injury, or surgeryto either hip, knee, or ankle and2) currently not taking prescriptionmedication for pain. Approval for thestudy was obtained from the IthacaCollege Human Subjects ReviewBoard. Prior to any testing, informedconsent forms were signed by all par-ticipants.Procedure

All subjects participated in two20-minute sessions separated by atleast 72 hours of rest. On the firstday, patient medical screening andselected physical characteristics wereassessed. Leg dominance was assessedby asking the subject to take a stepforward and kick a soccer ball whichwas rolling toward the center of theirlegs "as if you were kicking a ball intoa soccer goal."

FunctionalTestOn the day of functional testing,

the subject warmed up for 5 minuteson a stationary bike. Following this,the subject received an explanationof the one-legged hop for distance.Subjects were asked to stand on oneleg and their heel was positioned ona piece of athletic tape, which wasaffixed to a standard linoleum blockfloor. Subjects were instructed tokeep both hands behind their backto eliminate their use in generatingmomentum. The subject was thenasked to execute three warm-ups byhopping horizontally and landing onthe supporting leg. This was followedby a 30-second rest. Finally, threemaximal efforts, with the subject h o pping as far as possible, were exe-cuted. The subject was required toland on one leg. Failure to land onthe supporting leg resulted in a re-hop. This occurred in approximately5 1 0 % of the subjects. Prior to maxi-mal hopping, charcoal was placed onthe heel of the subject's shoe to markthe floor surface upon landing. Mea-surements were taken from heel toheel with a standard measuring tape.Following each hop, the subject waspositioned 2 feet lateral to the previ-ous hop. Large cardboard plates wereplaced over the recorded mark of theprevious hop to eliminate its use as avisual cue. The subject then repeatedthis protocol two more times for atotal of three trials. The same proto-col on the opposite leg was then per-formed. The leg tested first was ran-domized by a coin flip. No audiocues were given and subjects wereasked to wear the same pair of ath-letic shoes on both testing days.lsokinetic Test

On the day of isokinetic testing,the subjects had their right and leftquadriceps evaluated on a Kinetic-Communicator (Kin-Com, ChattecxCorp., Chattanooga, TN) . The su bject was stabilized in a seated positionwith four Velcro@ traps. Individual

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R E S E A R C H S T U D Y- . , . - . . ...~ - .--.- -.-. ---

I Dominant I147.40 143.40

160 100Dlmnce 140 Average goJumped Peak 80(cm) 120 Torque 70100 (Nm) 6080 5060 4040 302020 10

0 0Functional Test lsokinetic TestFIGURE. Mean values and standard deviation o fdominant and nondominant distance hopped (cm)and dominantand nondominant average peak toqu e (Nm)o f he quadriceps at 240sec.straps stabilized the trunk, waist,thigh, and leg. Stabilization at the legwas as far distal as possible, while stillallowing full dorsiflexion at the an-kle. The subject executed five s u bmaximal concentric warm-ups at240/sec followed by one maximalconcentric contraction at 240/sec.Following a 60-second rest, the s u bject executed three maximal concen-tric extensions at 240/sec, which wererecorded and used for data collection.The same protocol was repeated onthe contralateral leg. The leg testedfirst was randomized as well as the or-der of testing days. The test speed of240/sec wa. chosen secondary to itsfunctional nature. Functional activitiessuch as walking, jogging, running, andhopping all require angular velocitiesat the knee of speed in excess of200/sec. However, a limitation of theKinGom is that its fastest speed is300/sec. Twehundred-and-forty de-grees/*~ were determined to be aspeed which was most frequently usedfor testing in the clinic and was closerto angular velocities which may be oc-cumng at the knee during the one-legged hop for distance. Similar speedsof 300/sec and 270/sec were used byBarber et al (4) and Lephart et al (18),respectively. Both of these studies ex-amined the relationship between func-tional testing and physical characteris-tics, including isokinetic testing.

Data AnalysisMeans and standard deviationswere calculated for all variables.Scores on the functional test repre-sented a mean of the three maximaleffort hops. Scores on the isokinetictest represented the average peaktorque of the three maximal effortconcentric extensions. Paired t testswere used to compare the dominantwith the nondominant limb. Pearsonproduct moment correlation coeffi-cients were used to determine therelationship between the functionaltest and isokinetic test for both thedominant and nondominant limb.An alpha level of .05 was used to de-termine the significance level for allanalyses.

RESULTSPaired t tests comparing mean

distance hopped in cm revealed nosignificant difference between thedominant and nondominant limb onthe functional performance test noron the isokinetic test at 240/sec(Figure). Pearson product momentcorrelation coefficients revealed astatistically significant correlation( p< .05) between the distancehopped and the average peak torquefor the dominant ( r = .782) and thenondominant ( r = .649) leg.

DISCUSSIONResults of this study revealed that

no significant difference existed be-tween the dominant and nondomi-nant limb when testing with the one-legged hop for distance. This findingagrees with the study by Barber et al(4) who also found no significantdifference between dominant andnondominant limbs. When testingisokinetically at 240/sec, no signifi-cant difference was found betweenthe dominant and nondominantlimb. This finding, too, is in agree-ment with a study by Hageman et al(13) who tested dominant and non-dominant concentric quadricepsstrength on a KinGom. However, thetests were performed at velocities of30 and 180/sec slower then whatwere used in this study.

Only a moderate correlation ex-isted for both dominant and non-dominant limbs when comparing thefunctional test with the isokinetictest. These results are consistent withthe finding of other authors, such asTegner e t al (26), Tibone et al (27),Lephart et al (18), and Barher et al(4 ), who found a low correlation be-tween isokinetic testing and othervarious functional test.. Tegner et al(26) reported that 35% of patientswith ACL deficiency had normalquadriceps strength at 30/sec, butfailed to achieve normal values on aperformance test consisting of figure-eight running, a one-legged hop,running up and down a special stair-case, and running u p and down aslope.

Tibone et al (27), while studyinga functional analysis of anterior cruci-ate ligament instability, stated thatachieving quadriceps torque of 96%of the uninvolved limb was not sufi-cient to eliminate the subjective needfor surgical reconstruction. In addi-tion, Tibone et al stated that eventhough adequate quadriceps strengthwas attained, the patient continuedto demonstrate a significant differ-ence between limbs with a crosscutmaneuver. Lephart et al (20) re-Volume 22 Number 5 November 1995 JOSPT


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ported results consistent with Tiboneet al (27) when recording isokineticpeak torque deficits in patients withACL insufficiency.

Barber et al (4), while testingpatients with healthy and ACMefi-cient knees, stated that "no correla-tion" existed between results at 60/sec and 300/sec and four functionaltests, including a one-legged verticalhop, a one-legged timed hop, andtwo shuttle run tests. However, Bar-ber et al did report a statistically sig-nificant relationship with the 60/secquadriceps percent deficit scores andabnormal symmetry scores in a one-legged ho p for distance in patientswith ACL deficiency.

Isokinetic strength testing alonemay be an insufficient criterion forreturning patients to functional activ-ities. Several authors have stated thatdynamic functional capacity cannotbe ascertained from isokineticstrength performance (1 8,21), andthe results of this study support thisbelief. However, one single func-tional performance test may also beinsufficient in the dynamic assess-ment of a patient's functional level.Rather, several functional perfor-mance tests may need to be used toattain a functional profile and attainan accurate assessment of a patient'sfunctional level and readiness to re-turn to activity. This suggestion isconsistent with the beliefs of Gray(11 ) and Harter et al (14),who statethere is no one single adequate mea-sure of function.

The belief that functional perfor-mance test.., when compared withisokinetic measurements, mimic amore functional environment is wellsupported (17-21,23). However, alimitation which exists with this studyis the lack of tested validity. Unfortu-nately, the validity of the one-leggedhop for distance and most otherfunctional performance tests whichare believed to better mimic func-tional activities is unknown (4 ) and,in some cases, reliability has no t beentested. However, the one-legged hopfor distance has been found to be

reliable with healthy subjects in stud-ies by Hu et al (15), who found ICCvalues ranging from .79 to .96. In ourlab (12). 27 subjects with n o priorhistory of lower extremity injury wereused to evaluate the reliability of aone-legged hop for distance. Theprotocol used was the exact protocolused in this current study. Intraclasscorrelation coefficient values rangedfrom .92 to .96, indicating a high de-gree of reliability.

It is important to continue thistype of research on various other reli-able functional performance tests todetermine how they correlate withisokinetic strength tests. Finally, fur-ther research in the area is needed toinvestigate if the same correlationexists with various patient popula-tions.

CONCLUSIONThe results of this study support

the belief of other researchers thatisokinetic strength does not correlatestrongly with functional tasks. There-fore, in the assessment of healthysubjects, isokinetic strength alonemay not be an appropriate determi-nant of a subject's functional leveland ability to return to functionalactivities. This information helpsdemonstrate the need to developmore functional performance testssimilar to the one-legged hop fordistance, which will help to betterassess a patient's dynamic func-tional level and readiness to returnto activity. JOSPT

ACKNOWLEDGMENTSThe authors acknowledge the

editorial contributions of BarbaraIlelyea, PT, Charles Ciccone, PhD,IT, Carl Kukulka, PhD, PT, ndShree Pandya, MS, PT. We also thankSue Barber-Westin for her assistancein the preparation of the manuscript.

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R E S E A R C H S T U D Y- --- -sufficiency. Am J Sports Med 16:434-443, 198815. Hu HS, Whitney SL, lrtgang JJ, JanoskyJ: Test retest reliability of the one leggedvertical jump test and the one leggedstanding hop test. Presented at the an-nual combined sections meeting of theAmerican Physical Therapy Association,San Francisco, CA, February, 199216. Kannus P, Jarvinnen M: Conservativelytreated tears of the anterior cruciate lig-ament. Long term results. J Bone JointSurg 69A:lOO7-lOl2, 198717. Lephart SM, Perrin DH, Fu FH, GeickJH, lrrgang JJ, McCue FC, Weltmen A:Functional assessment of the anteriorcruciate ligament insufficient athlete.Med Sci Sports Exerc 2O(Suppl):2, 1988(abstract)18. Lephart SM, Perrin DH, Fu FH, GeickJH, McCue FC, Irtgang JJ: Relationshipbetween selected physical characteris-tics and the anterior cruciate ligamentinsufficient athlete. J Orthop SportsPhys Ther 16:174-181, 199219. Lephart SM, Perrin OH, Fu FH, MingerK: Functional performance tests for theanterior cruciate ligament insufficientathlete. J Natl Athl Train Assoc 26:44-50, 1991

20. Lephart SM, Perrin DH, Minger K, FuFH, Geick JH:Sports specific functionalperformance tests for the ACL ligamentinsufficient athlete. J Natl Athl TrainAssoc 24:119, 1989 (abstract)2 1. Mangine RE: Rules for objective func-tional testing, course notes from 1989Advances on the Knee and Shoulder,Cincinnati, OH, March, 198922. Noyes FR, BarberSD, Mangine RE: Ab-normal lower limb symmetry deter-mined by function hop tests after ante-rior cruciate ligament rupture. Am JSports Med 19513-518, 199123. Palmitier RA, An KN, Scott SG, ChaoEYS: Kinetic chain exercises in kneerehabilitation. Sports Med 6:402-4 13,199124. Shelbourne KD, Nitz P: Accelerated re-habilitation after anterior cruciate liga-ment reconstruction. Am J Sports Med18:292-299, 199025. Straub T, Hunter RE: Acute anteriorcruciate ligament repair. Clin Orthop227:238-250, 198826. Tegner Y, Lysholm 1, Lysholm M,Gillquist 1: A performance test to mon-itor rehabilitation and evaluate anteriorcruciate ligament injuries. Am J SportsMed 14:156-159, 1986

27. Tibone JE, Antich TI, Fanton GS,Moynes DR, Perry J: Functional analy-sis of anterior cruciate ligament insta-bility. Am J Sports Med 14:276-284,198628. Vaz M, Kramer1, Rorabeck C, BourneR: Isometric hip abduction strength fol-lowing total hip replacement and itsrelationship to functional assessment.Orthop Sports Phys Ther 18:526-53 1,199329. Voight M, Bell S, Rhodes D: Instru-mented testing of tibia1 translation dur-ing a passive lachman's test and se-lected closed chain activities inanterior cruciate ligament deficientknees. Presented at the combined sec-tions meeting of the American PhysicaTherapy Association, San Francisco,CA, February, 199230. Wi lk KE, Andrews JR: Current conceptsin the treatment of anterior cruciate lig-

ament disruption. 1Orthop Sports PhysTher 15:279-293, 19923 1. Yack HI, Collins CE, Whieldon TI:Comparison of closed and open kineticchain exercise in the anterior cruciateligament-deficient knee. Am J SportsMed 2 1 49-54, 1993

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