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 expenditu re (dE/dt) during different modes of human muscle action in vivo. dE/d t for the quadriceps muscle was expressed as: dE(quad)/dt = K1(omega) + K2(Tiso) + dW/dt, where K1 and K2 are constants, (omega) is joint an gular velocity (degrees/sec), (Tiso) represents the knee extension tor que 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). V olunteers 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, a nd net energy expenditure (E) above resting and dE/dt were determined for each muscle action. The best fit values for K1 and K2 for concentr ic, eccentric, and isometric muscle actions were 0.044, -0.55, and 0 W /degrees/sec, and 4.14, 5.28, and 2.17 W/N-m, respectively. The coeffi cients of determination (r(2)) for the model predictions of dE(quad)/d t for the three modes of muscle action were 0.78, 0.71, and 0.71, resp ectively. The correlation coefficient between predicted and experiment al dE/dt for all modes of muscle action combined was 0.93. These findi ngs indicate the model provides a useful tool for predicting the rate of energy expenditure associated with cyclic knee extension efforts.