Abstract
The oxygen cost of transport per unit distance (CoT; mL·kg-1·km-1) shows a U-shaped curve as a function of walking speed (v), which includes a particular walking speed minimizing the CoT, so called economical speed (ES). The CoT-v relationship in running is approximately linear. These distinctive walking and running CoT-v relationships give an intersection between U-shaped and linear CoT relationships, termed the energetically optimal transition speed (EOTS). This study investigated the effects of subtracting the standing oxygen cost for calculating the CoT and its relevant effects on the ES and EOTS at the level and gradient slopes (±5%) in eleven male trained athletes. The percent effects of subtracting the standing oxygen cost (4.8 ± 0.4 mL·kg-1·min-1) on the CoT were significantly greater as the walking speed was slower, but it was not significant at faster running speeds over 9.4 km·h-1. The percent effect was significantly dependent on the gradient (downhill > level > uphill, P < 0.001). The net ES (level 4.09 ± 0.31, uphill 4.22 ± 0.37, and downhill 4.16 ± 0.44 km·h-1) was approximately 20% slower than the gross ES (level 5.15 ± 0.18, uphill 5.27 ± 0.20, and downhill 5.37 ± 0.22 km·h-1, P < 0.001). Both net and gross ES were not significantly dependent on the gradient. In contrast, the gross EOTS was slower than the net EOTS at the level (7.49 ± 0.32 vs. 7.63 ± 0.36 km·h-1, P = 0.003) and downhill gradients (7.78 ± 0.33 vs. 8.01 ± 0.41 km·h-1, P < 0.001), but not at the uphill gradient (7.55 ± 0.37 vs. 7.63 ± 0.51 km·h-1, P = 0.080). Note that those percent differences were less than 2.9%. Given these results, a subtraction of the standing oxygen cost should be carefully considered depending on the purpose of each study.
Highlights
It has been well acknowledged that walking and/or running economy can be described as the oxygen cost of transport per unit distance (CoT; mLÁkg-1Ákm-1) [1,2]
Economical Walking Speed and Gait Transition Speed at Different Gradients relationship between CoT and gait speeds during walking [1,2,3,4,5,6,7] and a linear relationship during running [1]. This indicates that there is a particular gait speed minimizing the CoT in each individual during walking, and this gait speed is known as the economical speed (ES) [4,5,6,7] or optimal speed [8,9,10,11,12]
The net CoT was significantly lower than the gross CoT at all gait speeds at each gradient (P < 0.001, Fig 1)
Summary
It has been well acknowledged that walking and/or running economy can be described as the oxygen cost of transport per unit distance (CoT; mLÁkg-1Ákm-1) [1,2]. Economical Walking Speed and Gait Transition Speed at Different Gradients relationship between CoT and gait speeds during walking [1,2,3,4,5,6,7] and a linear relationship during running [1]. The standing VO2 accounted for 60% of the total VO2 at slower gait speeds [13]
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