Metabolic cost of level,uphill,and downhill running in highly cushioned shoes with carbon-fiber plates

Background:Compared to conventional racing shoes,Nike Vaporfly 4% running shoes reduce the metabolic cost of level treadmill running by4%.The reduction is attributed to their lightweight,highly compliant,and resilient midsole foam and a midsole-embedded curved carbon-fiber plate.We investigated whether these shoes also could reduce the metabolic cost of moderate uphill(+3°) and downhill(-3°) grades.We tested the null hypothesis that,compared to conventional racing shoes,highly cushioned shoes with carbon-fiber plates would impart the same ~4%metabolic power(W/kg) savings during uphill and downhill running as they do during level running.Methods:After familiarization,16 competitive male runners performed six 5-min trials(2 shoes × 3 grades) in 2 Nike marathon racing-shoe models(Streak 6 and Vaporfly 4%) on a level,uphill(+3°),and downhill(-3°) treadmill at 13 km/h(3.61 m/s).We measured submaximal oxygen uptake and carbon dioxide production during Minutes 4-5 and calculated metabolic power(W/kg) for each shoe model and grade combination.Results:Compared to the conventional shoes(Streak 6),the metabolic power in the Vaporfly 4% shoes was 3.83%(level),2.82%(uphill),and2.70%(downhill)less(all p <0.001).The percent of change in metabolic power for uphill running was less compared to level running(p=0.04;effect size(ES)=0.561) but was not statistically different between downhill and level running(p=0.17;ES=0.356).Conclusion:On a running course with uphill and downhill sections,the metabolic savings and hence performance enhancement provided by Vaporfly 4% shoes would likely be slightly less overall,compared to the savings on a perfectly level race course.