Energy cost of walking and running at extreme uphill and downhill slopes

<jats:p>The costs of walking (Cw) and running (Cr) were measured on 10 runners on a treadmill inclined between −0.45 to +0.45 at different speeds. The minimum Cw was 1.64 ± 0.50 J · kg<jats:sup>−1</jats:sup>· m<jats:sup>−1</jats:sup>at a 1.0 ± 0.3 m/s speed on the level. It increased on positive slopes, attained 17.33 ± 1.11 J · kg<jats:sup>−1</jats:sup>· m<jats:sup>−1</jats:sup>at +0.45, and was reduced to 0.81 ± 0.37 J · kg<jats:sup>−1</jats:sup>· m<jats:sup>−1</jats:sup>at −0.10. At steeper slopes, it increased to reach 3.46 ± 0.95 J · kg<jats:sup>−1</jats:sup>· m<jats:sup>−1</jats:sup>at −0.45. Cr was 3.40 ± 0.24 J · kg<jats:sup>−1</jats:sup>· m<jats:sup>−1</jats:sup>on the level, independent of speed. It increased on positive slopes, attained 18.93 ± 1.74 J · kg<jats:sup>−1</jats:sup>· m<jats:sup>−1</jats:sup>at +0.45, and was reduced to 1.73 ± 0.36 J · kg<jats:sup>−1</jats:sup>· m<jats:sup>−1</jats:sup>at −0.20. At steeper slopes, it increased to reach 3.92 ± 0.81 J · kg<jats:sup>−1</jats:sup>· m<jats:sup>−1</jats:sup>at −0.45. The mechanical efficiencies of walking and running above +0.15 and below −0.15 attained those of concentric and eccentric muscular contraction, respectively. The optimum gradients for mountain paths approximated 0.20–0.30 for both gaits. Downhill, Cr was some 40% lower than reported in the literature for sedentary subjects. The estimated maximum running speeds on positive gradients corresponded to those adopted in uphill races; on negative gradients they were well above those attained in downhill competitions.</jats:p>