Modeling energy expenditure associated with isometric, concentric, and eccentric muscle action at the knee.

This study was designed to derive and test a model of energy expenditure (dE/dt) during different modes of human muscle action in vivo. dE/dt for the quadriceps muscle was expressed as: dEquad/dt = Kl(omega) + K2(Tiso) + dW/dt. where K1 and K2 are constants, (omega) is joint angular velocity (degree/sec), (Tiso) represents the knee extension torque that could be developed by the active muscle if the muscle action were isometric (N-m), and (dW/dt) is the rate of work performed (W). Volunteers performed a series of repetitive 2- to 4-min knee extension exercises, while varying either the knee extension torque or velocity. The average joint torque, angular velocity, rate of work performed, and net energy expenditure (E) above resting and dE/dt were determined for each muscle action. The best fit values for K1 and K2 for concentric, eccentric, and isometric muscle actions were 0.044, -0.55, and 0 W/degree/sec, and 4.14, 5.28, and 2.17 W/N-m, respectively. The coefficients of determination (r2) for the model predictions of dEquad/dt for the three modes of muscle action were 0.78, 0.71, and 0.71, respectively. The correlation coefficient between predicted and experimental dE/dt for all modes of muscle action combined was 0.93. These findings indicate the model provides a useful tool for predicting the rate of energy expenditure associated with cyclic knee extension efforts.