One proposed hypothesis for gait transition (Margaria, 1963) is to minimize energy expenditure, thereby reducing metabolic cost. Farley and Taylor (1991) and Hreljac (1993), however presented data on O2 consumption which contradicts this hypothesis and suggested that some mechanical parameters may influence gait transition. A kinetic analysis ofnonpreferred speeds may lead to the identification of selected kinetic parameters which may influence gait transition.

The purpose ofthis study was to analyze the kinetics ofthe lower extremity for preferred and nonpreferred walking and running. The analysis focused on the changes that occurred in specific kinetic parameters between preferred and nonpreferred conditions. The kinetic analyses also included calculation ofsegmental interactions using the intersegmental dynamics approach (e.g., Putnam, 1983).

Three experienced male runners participated in the study. Six locomotor conditions were analyzed for each subject, including:​ two preferred walking and two preferred running conditions, and one nonpreferred walking and nonpreferred running condition. High speed video (200 Hz) and force plate data (500 Hz) were collected and analyzed and served as input to the kinetic equations of motion.

Results showed differences in generalized muscle moment patterns between the preferred and nonpreferred walking conditions, but not between running conditions. These differences were further manifested as changes in motion dependent torque interactions, particularly the torque due to the linear acceleration ofthe hip (AHIP). At the end ofswing the segmental interaction ofthe nonpreferred walk was similar to that in running, however an additional torque acting in the same direction as the GMM was present in all running conditions, but not the nonpreferred walk.

Nonpreferred walking may be considered nonpreferred due to changes in the lower extremity mechanics as suggested by differences in the kinetic parameters analyzed. The running conditions displayed similar patterns for all kinetics variables, suggesting that the nonpreferred run was not categorized as nonpreferred because of changes in mechanics. The nonpreferred run may be considered nonpreferred due to energetic demands, based on data which show that running at very slow speeds was most energetically costly than walking at that same speed (e.g., Hreljac, 1993).