Sweat lactate results from eccrine gland metabolism, however, the possible clearance of blood lactate through sweat has not been resolved. On separate days in an environmental chamber (32 +/- 1 C) 12 subjects completed a constant load (CON) (30 min at 40% VO2 max) and an interval cycling trial (INT) (15 one-min intervals at 80% VO2 max, each separated by one min rest) each designed to elicit different blood lactate responses. Each 30 min cycling trial was preceded by 15 min warm-up (30 watts) and followed by 15 min passive rest. Sweat and blood were analyzed for lactate concentration at 15, 25, 35, 45, and 60 min during CON and INT. Total body water loss was used to calculate sweat rate (ml/hr). Blood lactate was significantly greater (p < or = 0.05) at 25, 35, 45, and 60 min during INT compared to CON (approximately 5 mmol/L vs 1.5 mmol/L). Sweat lactate was not significantly different (p>0.05) between trials at any time (approximately 10 mmol/L). Sweat rates (approximately 600ml/hr) and estimated total lactate secretion were not significantly different (CON vs. INT) (p > 0.05). Elevated blood lactate was not associated with changes in sweat lactate concentration. Sweat lactate seems to originate in eccrine glands independent of blood lactate.

Research on gender differences in ratings of perceived exertion (RPE) has been equivocal with few studies comparing exercise modes and differentiated RPE. The current study examined gender differences in overall and differentiated RPE at the respiratory compensation threshold (RCT) during cycling and treadmill exercise. Each minute during a maximal treadmill and maximal cycling test, men (n=18) and women (n=16) estimated RPE corresponding to overall (RPE-O), legs (RPE-L), and breathing/chest (RPE-C) exertion. A 2 (gender) x 2 (mode) x 3 (RPE-O, RPE-L, RPE-C) repeated measures MANOVA revealed no significant mode x gender or RPE x gender interactions. The exercise mode x RPE interaction approached significance (P=0.055) when cycling [mean (SD) 14.8 (2.9)] and treadmill exercise [12.8 (2.9)] were compared. No main effects for gender [men: 13.7 (2.6), women: 13.4 (2.6)] were detected. Main effects for mode showed RPE to be significantly greater during cycling [14.4 (2.8)] versus treadmill exercise [12.7 (2.9)]. Main effects for differentiated RPE showed RPE-L [13.8 (2.6)] to be significantly greater than RPE-O [13.5 (2.6)] and RPE-C [13.3 (2.6)]. Results suggest that overall and differentiated RPE at the RCT are not significantly different between genders during cycling or treadmill exercise. While RPE-L was statistically greater than RPE-O and RPE-C, the magnitude of the differences makes this result of little practical significance. The marginal interaction suggests greater RPE-L values might be expected at the RCT during cycling versus treadmill exercise. However, results suggest that minimal RPE differences exist between men and women during cycling and treadmill exercise.

Sweat lactate indirectly reflects eccrine gland metabolism. However the potential influence of aerobic fitness on sweat lactate is not well-understood. Six males with high aerobic fitness [peak oxygen consumption ( VO(2)peak): 61.6 (2.5) ml.kg(-1).min(-1)] and seven males with low aerobic fitness [ VO(2)peak: 41.8 (6.4) ml.kg(-1).min(-1)] completed a maximal exertion cycling trial followed on a different day by 60 min of cycling (60 rev.min(-1)) in a 30 degrees C wet bulb globe temperature environment. Intensity was individualized at 90% of the ventilatory threshold ( V(E)/ VO(2) increase with no concurrent V(E)/ VCO(2) increase). Sweat samples were collected from the lumbar region every 10 min and analyzed for lactate concentration. Sweat rate (SR) was significantly greater ( p<0.05) for subjects with a high [1445 (254) ml.h(-1)] versus a low [1056 (261) ml.h(-1)] fitness level. Also, estimated total lactate excretion (SRxmean sweat lactate concentration) was marginally greater ( p=0.2) in highly fit males. However, repeated measures ANOVA showed no significant differences ( p>0.05) between groups for sweat lactate concentration at any time point. Current results show highly fit (vs. low fitness level) males have a greater sweat rate which is consistent with previous literature. However aerobic fitness and subsequent variations in SR do not appear to influence sweat lactate concentrations in males.