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

Abstract

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.

Keywords: Economical speed; Energy expenditure; Heart rate; Hot environment; Pulmonary ventilation.

Fig. 1.

Changes in (A), (B), (C), and EE (D) at all gait speeds in thermoneutral (○; 23°C), cool (Δ; 13°C), and hot (●; 33°C) conditions. Values are means±standard deviation (s.d.). oxygen uptake; , carbon dioxide output; , pulmonary ventilation; EE, energy expenditure. *P<0.05 between 33°C and 13°C, ^†P<0.05 between 33°C and 23°C.

Fig. 2.

Changes in HR at all gait speeds in thermoneutral (○; 23°C), cool (Δ; 13°C), and hot (●; 33°C) conditions. Values are means±s.d. HR, heart rate. * and ^† indicate the same as in Fig. 1.

Fig. 3.

Changes in T_sk at all gait speeds in thermoneutral (○; 23°C), cool (Δ; 13°C), and hot (●; 33°C) conditions. Values are means±s.d. T_sk, mean skin temperature. * and ^† indicate the same as in Fig. 1.

Fig. 4.

Changes in Cw (A), averaged Cw during slower and faster three stages (B), and comparisons of the economical speed (C) in three environmental conditions. Values of plots (A) and bar graphs (B,C) are means±s.d. In A, each mark indicates the same as in Fig. 1, and each line curve was obtained using a quadratic function. In C, each line graph indicates an individual data of the ES. Cw, energy cost of walking; ES, economical speed. * and ^† indicate the same as in Fig. 1.

Fig. 5.

Changes in RPE (A) and VAS (B) at all gait speeds in three environmental conditions. Values are means±s.d. RPE, rate of perceived exertion; VAS, visual analogue scale. In A, marks on the line graph indicate the same as in Fig. 1. In B, * indicates the same as in Fig. 1.