Impact of ambient temperature on energy cost and economical speed during level walking in healthy young males.

We measured oxygen consumption and carbon dioxide output during walking [per unit distance ( Cw ) values] for 14 healthy young human males at seven speeds from 0.67 to 1.67 m s-1 (4 min per stage) in thermoneutral (23°C), cool (13°C), and hot (33°C) environments. The Cw at faster gait speeds in the 33°C trial was slightly higher compared to those in the 23°C and 13°C trials. We found the speed at which the young males walked had a significant effect on the Cw values ( P <0.05), but the different environmental temperatures showed no significant effect ( P >0.05). Economical speed (ES) which can minimize the Cw in each individual was calculated from a U-shaped relationship. We found a significantly slower ES at 33°C [1.265 (0.060) m s-1 mean (s.d.)] compared to 23°C [1.349 (0.077) m s-1 ] and 13°C [1.356 (0.078) m s-1 , P <0.05, respectively] with no differences between 23°C and 13°C ( P >0.05). Heart rate and mean skin temperature responses in the 33°C condition increased throughout the walking trial compared to 23°C and 13°C (all P <0.05). These results suggest that an acutely hot environment slowed the ES by ∼7%, but an acutely cool environment did not affect the Cw and ES.