Sweat lactate response during cycling at 30°C and 18°C WBGT

Sweat lactate reflects eccrine gland metabolism. However, the metabolic tendencies of eccrine glands in a hot versus thermoneutral environment are not well understood. Sixteen male volunteers completed a maximal cycling trial and two 60-min cycling trials [30degreesC = 30+/-1degreesC and 18degreesC = 18+/-1degreesC wet bulb globe temperature (WBGT)]. The participants were requested to maintain a cadence of 60 rev . min(-1) with the intensity individualized at similar to 90% of the ventilatory threshold. Sweat samples at 10, 20, 30, 40, 50 and 60 min were analysed for lactate concentration. Sweat rate at 30degreesC (1380+/-325 ml . h(-1) ) was significantly greater ( P <0.05) than at 18degreesC (632+/-311 ml . h(-1) ). Sweat lactate concentration was significantly greater ( P <0.05) at each time point during the 18degreesC trial, with values between trials tending to converge across time. During the 30degreesC trial, both heart rate (20, 30, 40, 50 and 60 min) and rectal temperature (30, 40, 50 and 60 min) were significantly higher than in the 18degreesC trial. Higher sweat lactate concentrations coupled with lower sweat rates may indicate a greater relative contribution of oxygen-independent metabolism within eccrine glands during exercise at 18degreesC. Decreases in sweat lactate concentration across time suggest either greater dilution due to greater sweat volume or increased reliance on aerobic metabolism within eccrine glands. The convergence of lactate concentrations between trials may indicate that time-dependent modifications in sweat gland metabolism occur at different rates contingent partially on environmental conditions.