Evaluation of a Newly-Designed, Dynamic Knee Extension Device for the Study of Muscle Fatigue in Humans

A device utilizing a simple pulley system was developed to study muscle fatigue during dynamic, submaximal exercise isolated to the knee-extensor muscles of one or both legs. The purposes of this study were to determine the following 1 oxygen consumption requirements for various submaximal and maximal power outputs and to compare these data to values obtained from published reports using modified bicycle ergometers criterion devices, 2 intraindividual test-retest variability, and 3 muscle fatigability during exercise. On each of 2 separate days, 8 male volunteers mean age 18.6 or - 0. 3 yr SE, weight 79.5 or 5.1 kg, and height 179.1 or - 2.0 cm performed a graded, intermittent 4 min bouts exercise test using the knee-extensor muscles of one leg to determine one-legged peak oxygen consumption. Maximal voluntary contractions MVC were obtained at the beginning, at 2 min, and at the end of each exercise bout as a means to monitor rate of muscle fatigue. The slope and intercept of the relationship of the increase in power output and oxygen consumption were 13.80 ml O2,watt and 470 mlmin, respectively, with r2 0.96. These values for slope and intercept are similar to those reported previously slopes 13.10 and 14.70 ml O2,watt intercepts, 400 and 471 mlmin and r2 0. 99. Also, there was minimal intra-individual variation r2 0.90 in oxygen consumption values for identical power outputs. Test-retest oxygen consumption values did not differ from a line of identity. Stepwise accelerations in muscle fatigability were discernable with small increments in exercise intensity and elapsed exercise time. Our device represents a low-cost, expanded capability alternative compared to previous units utilizing modified bicycle ergometers as a testing mode.