On methods of evaluation of lower extremity eccentric muscle performance and loading

Abstract: This investigation has developed and evaluated methods for measuring eccentric muscle functionand loading of the human lower extremity, including isokinetic tests of knee extensor muscleperformance and a comprehensive in vivo method for conditions of functional loading. Formeasurement of knee extensor muscle performance, a protocol of 100 repetitive maximal actionsat 90¡ s~' was applied using a Biodex isokinetic dynamometer. The test-retest reliability wasstudied in sixteen healthy volunteers. Intra Class Correlation coefficients (ICCs) for eccentricknee extensor endurance indicated high reliability for total work (Joules) and absolute endurance(ICC, 0.92 and 0.93) but not for relative endurance (ICC, 0.71). The validity of this test withreference to treadmill running capacity was studied in nine male elite middle-distance runners.Eccentric total work was significantly related to submaximal oxygen uptake (ml kg~0 75 min~') at allthree running velocities investigated (12, 14, and 15 km-h~~). The R2-values indicated that 48-59% of the variability in submaximal oxygen uptake could be explained by the level of eccentrictotal work. Further, the isokinetic test was used for describing knee extensor endurance inseventeen professional ballet dancers, a group exposed to daily repetitive eccentric loading, inrelation to a control group of moderately active subjects. Eccentric total work/kg was 31%greater for the dancers compared with the controls (p<0.001). The eccentric/concentric totalwork ratio was greater in the dancers (x =2.07) compared with the controls (x =1.74) (p<0.001). The isokinetic technique used guantifies isolated muscle performance. Whenstudying functional loading, the implementation of a comprehensive approach may be moreappropriate. A new experimental method integrating four different measurement systems wasdeveloped and tested in seven healthy volunteers. The surgical procedure for implantation of twotibia force transducers in local anesthesia was uncomplicated. The transducers consisted of straingauges mounted on a surgical staple and was designed to measure local bone deform tion. Forthe pilot study, two conditions of forefoot or heel landing after a standardized jump were studied.The local peak tibia deformation occurred at 20-42 ms (median) after ground contact and was upto eight times higher during stance phase loading compared to standing still on one leg.Systematic differences in ground reaction force and muscular activation patterns were observedfor the different conditions of foot strike. With this experimental method, the effect of moderateduration exercise on muscle activation characteristics, local tibia deformation, ground reactionforces, and lower extremity kinematics during standardized jumping and landing was studied infive volunteers. The peak vertical ground reaction force and tibia force transducer amplitudeoccurred earlier with respect to foot strike after 30 minutes of ergometer cycling at a perceivedheavy exertion level, the median changes were -22 ms (p=0.04) and -12 ms (p=0.04),respectively. This shift in timing of peak loads was not accompanied by a similar shift in time ofpeak lower extremity muscle activation. In summary, measurement of isokinetic eccentric knee extensor endurance may beutilized in clinical evaluation and research if issues of reliability and validity are considered. Thepresented comprehensive experimental in vivo method for simultaneous measurement of muscleactivity, ground reaction forces, local bone deformation, and joint motion may be of interest forfurther studies of loading conditions associated with the etiology of lower extremity overuseinjuries.Key words: Biomechanics, eccentric, electromyography, isokinetic, methods, muscle endurance,pilot projects, reproducibility of results, strain, thigh, tibia.ISBN 91-628-1793-0