NORDGREN, A; BUTCHER, MT; BERTRAM, JEA*; Florida State Univ., Tallahassee; Univ. of Calgary, Calgary; Univ. of Calgary, Calgary: External power production in walking and running under simulated gravity changes: correlation with metabolic cost

Studies have shown that the metabolic cost of running decreases with decreases in gravity (g) but this is only marginally the case for walking. Running costs will be related to the impulsive force applied during the contact of each step, so its relation to the magnitude of g makes sense. The apparent insensitivity to gravity level for walking cost is perplexing. However, if the cost of walking derives primarily from replacing mechanical energy lost at the transition between steps (a form of mechanical collision), then the cost of walking should be dependent on speed and less dependent on g. To test this hypothesis we studied walking and running in both decreased and increased gravity using a unique gravity simulation device. Metabolic cost for these conditions was measured using indirect calorimetry while subjects moved on a treadmill. Ground reaction force was measured while moving down a 10 m runway across four serially arranged force platforms within the gravity simulation device. External mechanical power was calculated for each limb independently; facilitated for simultaneous contacts in walking by the serial platform system. Metabolic and mechanical measurements were then compared. Unlike the reduced gravity situation where the cost of walking appeared insensitive to g, in hypergravity walking the metabolic cost increased, though not as sharply as running cost. Independent limb force and power were each dependent on gravity level for both walking and running. Changes in specific features of the ground reaction force profile during transition between contact limbs in walking did correlate with metabolic cost in the different gravity regimes.