The Maximal Short-Term Power Output of Human Leg Muscles During Isokinetic Cycling Exercise

Abstract

<p>Classical force-velocity studies by A. V. Hill demonstrated that there was an optimal velocity for maximal power output of isolated muscles and human movements. Thus to study muscle performance during maximal dynamic exercise it is important to measure mechanical power output at several constant velocities of movement. At the start of this work no instruments were available to measure maximal power during isokinetic movements over a wide range of velocities. For this reason a cycle ergometer (CVE) was developed which restricted the crank velocities to chosen upper limits, despite maximal efforts by the subject.</p> <p>Measurements were obtained in male subjects of maximal peak torque generated over 81% of the functional range. There was a consistent inverse linear relationship between peak torque, and crank velocity, and the results were reproducible from day to day. Considerable inter-subject variability in peak torque was accounted for only partly by differences in thigh muscle volume. Maximal peak power occurred at various crank velocities ranging from 120 to 160 rpm; differences in muscle fibre types may have contributed to the variation observed. Maximal power occurred when the force equalled 0.3 to 0.4 of the predicted maximal isometric tension, in agreement with Hill's studies.</p> <p>Torque, work and power were also measured during 30 s of maximal effort at 60, 100 and 140 rpm. Increases in crank velocity were associated with both a higher initial power, and a greater rate and extent of decline in power, but total work was similar. The greater decline at faster velocities may reflect differences in energy metabolism, or motor unit activation. In addition to defining the effects of velocity on maximal power output in healthy young subjects, the studies showed the CVE to be a sensitive, reliable instrument, with potential applications to the assessment of human muscle function in health and disease.</p>