Abstract

Compared with level walking or running, progressive downhill walking/running requires a decreasing energy cost to some minimum where the cost again increases with further decrements in grade. Margaria estimated this minimum occurs at a -9 grade. This study attempts to more precisely track the energy cost curve in progressive downhill treadmill walking. After VO2max determination subjects (10 men 22.0+-2.5 yr) performed 14 randomly ordered walking bouts of 6 min duration, at 90 and 105 m/min. Grades used were 0, -3, -6, -9, -12, -15, and -18. Net VO2 values decreased with decrements in grade to -9, -12 for the respective speeds of 90 and 105 m/min. Group mean net VO2 minimums at -9 and -12, however, were not significantly different from group mean values at -6 and -15 at 90 m/min, or between -9 and -15 grades at 105 m/min. Group mean net VO2 values at 0, -3, and -18 were significantly different from net VO2 values for the other grades at 90 m/min walking. At 105 m/min, mean net VO2 values at 0, -3, -6, and -18 were significantly different from net VO2 values at the other grades. We conclude that the energy cost curve for downhill walking does not precisely conform with the view that the minimum cost occurs at -9 grade. While a reasonable approximation, our group data suggest that this point is variable, between -6 and -15 grade depending on an individuals walking characteristics and walking speed. We also present a rationale to explain the energy cost curve observed during progressive downhill walking. Verf.-Referat