The relationship between exercise intensity and the sweat lactate excretion rate.

The purpose of this study was to determine the effect of increases in exercise intensity on the sweat lactate concentration and lactate excretion rate. Eight healthy male volunteers complete a 90-min exercise bout of treadmill walking in a 35 degrees C and 40% relative humidity environmental chamber. During the exercise trial, the subjects performed three 30-min ordered exercise bouts at 60, 70, and 80% of their age-predicted maximum heart rate (HR(max)), with 10 min of rest outside the chamber between bouts. Sweat rate was measured volumetrically during each of the three exercise bouts on the flexor surface of the proximal half of the right forearm. Sweat lactate concentration ([lactate](sweat)) was measured in each sample and multiplied by the forearm sweat rate to calculate the lactate excretion rate (LER). There was a significant (P < 0.05) decrease in the [lactate](sweat) at the 70 and 80% HR(max) exercise intensities compared to the 60% HR(max) exercise intensity. Conversely, the LER increased significantly at the highest two exercise intensities compared to the 60% HR(max) exercise intensity. Such data suggest that increases in exercise intensity require an increase in lactate production, as measured by the LER. Furthermore, the decreased [lactate](sweat) at the higher exercise intensities is most likely the result of increased sweat production causing a dilution effect on the [lactate](sweat), thus limiting its ability to accurately indicate the metabolic activity of the sweat gland.