Plasma lactate accumulation is reduced during incremental exercise in untrained women compared with untrained men

The lactate threshold (LT) is commonly reported as not different between sexes, yet lower blood lactate concentrations have been reported in women during submaximal exercise. The purpose of the present study was to measure the changes in plasma lactate concentration [La−1] in men and women during incremental cycle ergometer exercise using the same protocol and compare the data using several different methods of analysis. A group of untrained men (n = 21) and women (n = 22) were studied and venous blood drawn at regular intervals during and after exercise for assay of plasma [La−1]. Plasma [La−1] increased during exercise in both sexes, reaching higher values in men, both at exhaustion (men 8.6 ± 2.3 mmol l−1; women 6.2 ± 2.3 mmol l−1; P = 0.01) and post-exercise (men 11.8 ± 2.1 mmol l−1; women 10.2 ± 2.4 mmol l−1; P = 0.03). Logarithmic transformation of the data yielded LT values that were not different between sexes (men 44.2 ± 12.9; women 50.2 ± 12.6; %V˙O2peak; P=0.45), yet both the 2 and 4 mmol l−1 fixed concentration LT occurred at lower relative intensities in men (2 mmol l−1: men 50.9 ± 12.9; women 66.9 ± 11.1; %VO2peak;P=0.01. 4 mmol l−1: men 75.7 ± 11.0; women 90.6 ± 9.2; V˙O2peak;P=0.01). However, when the plasma [La−1] was examined in both sexes throughout exercise, using a single exponential function, plasma [La−1] was significantly lower in women (P < 0.05) at all relative intensities between 30 and 100%V˙O2peak. While the basis of this sex difference is unknown, reduced plasma [La−1] during submaximal exercise in women may offset to some degree the endurance performance disadvantage of their lower VO2peak

Maximal oxygen uptake and lactate metabolism are normal in chronic fatigue syndrome

Purpose: Previous studies in chronic fatigue syndrome (CFS) have reported reductions in maximal oxygen uptake (VO(2max)), yet often the testing procedures have not followed accepted guidelines, and gender data have been pooled. The present study was undertaken to reevaluate exercise capacity in CFS patients by using "gold standard" maximal exercise testing methodology and stratifying results on a gender basis. Methods: Sixteen male and 17 female CFS patients and their gender-, age-, and mass-matched sedentary controls performed incremental exercise to volitional exhaustion on a stationary cycle ergometer while selected cardiorespiratory and metabolic variables were measured. Results: VO(2max) in male CFS patients was not different from control values (CFS: 40.5 +/- 6.7; controls: 43.3 +/- 8.6; mL x kg(-1) x min(-1)) and was 96.3 +/- 17.9% of the age-predicted value, indicating no functional aerobic impairment (3.7 +/- 17.9%). In female CFS patients, VO(2max) was lower than control values (CFS: 30.0 +/- 4.7; controls: 34.2 +/- 5.6; mL x kg(-1) x min(-1), P = 0.002), but controls were higher than the age-predicted value (112.6 +/- 15.4%, P = 0.008) whereas the CFS patients were 101.2 +/- 20.4%, indicating no functional aerobic impairment (-1.2 +/- 20.4%). Maximal heart rate (HR(max)) in male CFS patients was lower than their matched controls (CFS: 184 +/- 10; controls: 192 +/- 12; beats x min(-1); P = 0.016) but was 99.1 +/- 5.5% of their age-predicted value. In female CFS patients, HR(max) was not different from controls (CFS: 183 +/- 11; controls: 186 +/- 10; beats x min(-1)) and was 98.9 +/- 5.1% of the age-predicted value. The VO(2) at the lactate threshold (LT) in each gender group, whether expressed in mL x kg(-1) x min(-1) or as a percentage of VO(2max), was not different between CFS patients and controls. Conclusions: In contrast to most previous reports, the present study found that VO(2max), HR(max), and the LT in CFS patients of both genders were not different from the values expected in healthy sedentary individuals of a similar age