Energy expenditure and motor performance relationships in humans learning a motor task.

The ability of human subjects to learn minimum energy-demanding variants of biological motion was examined in three adult males trained to walk on hands and feet (creep) on a motor-driven treadmill at constant speed (0.64 m/s) for 16 3-min trials. Two subjects systematically decreased oxygen consumption and heart rate over trials. Following this acquisition phase, subjects completed walking and creeping trials at positive and negative treadmill grades and selected a freely chosen creeping grade that felt "most comfortable." One subject selected a grade that was more efficient than those imposed. Oxygen-consumption curves for walking and creeping converged with increasing positive grade, indicating that increased grade influences the metabolic energy viability of the task (creeping or walking). The acquisition data provide empirical support for the "principle of least effort" and lend support to the concept of a "comfort mode" in the execution of motor tasks.