| The metabolic power required to walk over level ground is determined by two primary mechanical tasks: body weight (BW) support and work done on the center of mass. However, it is not yet known how weight and mass contribute to metabolic power with varying uphill and downhill slopes. We hypothesized that BW and mass would each require significant, but opposing metabolic contributions to walk on uphill versus downhill slopes. We tested our hypotheses by measuring metabolic rates in 10 healthy subjects as they walked for 5 minutes under four general conditions: unaltered (UA), with reduced weight using simulated reduced gravity, added weight, and added mass alone. Participants walked under each of these conditions on level ground (0°), uphill (+3° and +6°), and downhill (-3° and -6°) slopes. We found that the percentage of net metabolic power (NMP) due to BW increased significantly from 19 +/- 18.4% on level ground up to 77 +/- 7.5% at +6°. Whereas the percentage of NMP due to BW, albeit not significantly different from level ground, was -5.0 +/- 22.6% and 2.9 +/- 37.6% at -3° and -6°, respectively. In contrast, the percentage of NMP due to mass was 29 +/- 14.3% on level ground, 18 +/- 12.2% at +6°, and 44 +/- 17.0% at -6°. In summary, we found that at steeper uphill slopes only, the percentage of NMP due to BW significantly increased. However, the percentage of NMP due to mass was not significantly different at any slopes compared to level ground. |
