Abstract
Oxygen uptake (V̇O2), heart rate (HR), energy cost (EC) and oxygen pulse are lower during downhill compared to level or uphill locomotion.
However, a change in oxygen pulse and EC during prolonged grade exercise is not well documented. This study investigated changes
in cardiorespiratory responses and EC during 45-min grade exercises. Nine male healthy volunteers randomly ran at 75% HR
reserve during 45-min exercise in a level (+1%), uphill (+15%) or downhill (−15%)
condition. V̇O2
, minute ventilation (V̇E
) and end-tidal carbon dioxide (PetCO2) were recorded continuously with 5-min averaging between the 10th and 15th min (T1) and 40th and 45th min (T2). For a similar HR (157±3 bpm), V̇O2
, V̇E
, and PetCO2 were lower during downhill compared to level and uphill conditions (p<0.01). V̇O2
and V̇E
decreased similarly from T1 to T2 for all conditions (all p<0.01), while PetCO2 decreased only for the downhill condition (p<0.001). Uphill exercise required greater
EC compared to level and downhill exercises. EC decreased only during the uphill condition between T1 and T2 (p<0.01). The lowest
V̇O2
and EC during downhill exercise compared to uphill and level exercises suggests the involvement
of passive elastic structures in force production during downhill. The lower cardiorespiratory
response and the reduction in PetCO2 during downhill running exercise, while EC remained constant, suggests an overdrive ventilation pattern likely due to a greater
stimulation of efferent neural factors.
Key words
treadmill running - oxygen uptake - uphill - downhill - energy cost
