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The minimum efficiency of loaded walking the uphill and downhill portions of the paths, was obtained by dividing the mechanical vertical (positive or negative) power by the associated metabolic power. Diamond and triangle symbols refer to experiments in Namche (3490 m a.s.l.) and at the Research Pyramid (5050 m a.s.l.), respectively (***p<0.001). Grey lines represent given (absolute) ratios between the positive and negative efficiencies.
