Blood flow and oxygen uptake increase with total power during five different knee-extension contraction rates

Controversies exist regarding quantification of internal power (IP) generated by the muscles to overcome energy changes of moving body segments when external power (EP) is performed. The aim was to 1) use a kinematic model for estimation of IP during knee extension, 2) validate the model by independent calculation of IP from metabolic variables (IPmet), and 3) analyze the relationship between total power (TP = EP + IP) and physiological responses. IP increased in a curvilinear manner (5, 7, 13, 21, and 34 W) with contraction rate (45, 60, 75, 90, and 105 contrations/min), but it was independent of EP. Correspondingly, IPmet was 5, 7, 10, 19, and 28 W, supporting the kinematic model. Heart rate, pulmonary oxygen uptake, and leg blood flow plotted vs. TP fell on the same line independent of contraction rate, and muscular mechanical efficiency as well as delta efficiency remained remarkably constant across contraction rates. It is concluded that the novel metabolic validation of the kinematic model supports the model assumptions, and physiological responses proved to be closely related to TP, supporting the legitimacy of IP estimates.