Mechanical and physiological responses to lower extremity loading during running

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Abstract
Highly trained men (15) performed treadmill running at 12 km/h to determine the effect of lower extremity loading on measures for 7 temporal and kinematic descriptors of the running cycle, the mechanical work done on the lower extremity O2 consumption .ovrhdot.VO2 and heart rate. Five load conditions (no added load and loads of 0.50 kg and 1.00 kg added to either the thighs or feet) were examined. .ovrhdot.VO2 and heart rate increased as load was increased on both the thighs and feet. All changes were statistically significant except for the heart rate changes due to thigh loading. The increases in .ovrhdot.VO2 due to foot loading .apprx. 7.2%/kg of load were nearly twice as great as those due to thigh loading. One kg added to the feet produced small but significant increases in stride length (1.4 cm), swing time (9 ms) and flight time (6 ms) and a decrease in peak ankle velocity (0.23 m .cntdot. s-1). No other load condition resulted in significant changes in any of the temporal and kinematic variables. The results for mechanical work demonstrated that significant increases in the work done on the leg were produced by the loading but that these increases were limited to the loaded segments. Consistent with the data for O2 consumption and heart rate, mechanical work was increased to a greater extent by foot loading than by thigh loading. The increased physiological demand was directly related to the mechanical work increases which in turn were attributed to the increased inertia of the loaded segments rather than modifications in the kinematics of the lower extremity movements.