PONTZER, Herman; Harvard University: The effect of limb length on locomotor performance

Does increased limb length improve energy efficiency or speed during locomotion? Despite proposals that longer limbs increase walking and running speed and decrease locomotor energy cost, physiological studies have shown no correlation between leg length and running performance, and only limited correlations for walking. This study developed and tested a new biomechanical model relating limb length to the metabolic cost of locomotion and speed in walking and running, further developing the �Force Production� model proposed by Kram and Taylor (Nature. 346: 265-267). The model is the first to explicitly link leg length to the rate of muscular force production, and thus the rate of oxygen consumption, during locomotion. To test the model, 9 recreationally fit human subjects performed a series of walking and running trials on a treadmill while oxygen consumption and kinematics were measured. Observed oxygen consumption data fit predictions of the model as well or better than observed contact time (running) and Froude number (walking), and significantly better than other anatomical predictors of cost. These results suggest that longer legs increase speed and decrease energy cost during walking and running, but that other factors such as excursion angle and knee compliance also affect cost, complicating this relationship. Further, the model provides a means of predicting locomotor costs from muscular force production that can be employed across gaits and, perhaps, across species.