Mechanical work in running

The external and internal mechanical work in running has been measured through various procedures. Different from walking, in running the work due to the forward speed changes (variation of kinetic energy) and to the vertical displacement of the center of gravity (variation of potential energy), throughout the step cycle, are substantially in phase. The external work performed per kilometer is independent of speed, amounting to 0.25 kcal/kg km. The total mechanical work amounts to about 0.40–0.50 kcal/kg km. The efficiency in running has been calculated as about 40–50%: such a high value involves a contribution of a substantial amount of energy delivered at a very low cost; this appears to be identified as elastic recoil energy from the stretched contracted muscle and amounts to about half the energy spent in running. A mechanical model is given for the walking and running processes. mechanics of locomotion; kinetic and potential energy during step cycle; elasticity of contracted muscle; mechanical models for walking and running Submitted on July 29, 1963