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

This investigation has developed and evaluated methods for measuring eccentric muscle function and loading of the human lower extremity, including isokinetic tests of knee extensor muscle performance and a comprehensive in vivo method for conditions of functional loading. For measurement of knee extensor muscle performance, a protocol of 100 repetitive maximal actions at 90° was applied using a Biodex isokinetic dynamometer. The test-retest reliability was studied in sixteen healthy volunteers. Intra Class Correlation coefficients (ICCs) for eccentric knee 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 with reference 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 all three 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 eccentric total work. Further, the isokinetic test was used for describing knee extensor endurance in seventeen professional ballet dancers, a group exposed to daily repetitive eccentric loading, in relation to a control group of moderately active subjects. Eccentric total work/kg was 31% greater for the dancers compared with the controls (p