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It has been shown that boys recover faster than men following brief, high-intensity exercise. Better to understand this difference, plasma metabolite concenration, volume, electrolyte concentration [electrolyte], and hydrogen ion concentration [H+] changes were compared in five prepubescent boys [mean age 9.6 (SD 0.9) years] and 5 men [mean age 24.9 (SD 4.3) years] following 30-s, all-out cycling. Blood was collected prior to, at the end, and at the 1st, 3rd and 10th min following exercise. At the 10th min of recovery, the men's lactate concentration was 14.2 (SD 1.8) mmol · l−1 and [H+] was 66.1 (SD 5.9) nmol · l−1, compared with 5.7 (SD 0.7) mmol · l−1 and 47.5 (SD 1.2) nmol · l−1 respectively, in the boys (P < 0.01 for both). The glycerol concentration was higher in the boys at the end of exercise and until the 3rd min of recovery. Plasma volume (PV) decreased more in the men [16.9 (SD 3.0)%] than in the boys [9.4 (SD 2.8)%]. In both groups, [electrolyte] increased after exercise, tending to be higher in the men. Recovery of plasma [electrolyte] and PV started earlier in the boys (1st min) than in the men (3rd min). These findings would support the notion of a lesser reliance on glycolytic energy pathways in children and may explain the faster recovery of muscle power in boys compared to men.

We attempted to determine the change in total excess volume of CO2 Output (CO2 excess) due to bicarbonate buffering of lactic acid produced in exercise due to endurance training for approximately 2 months and to assess the relationship between the changes of CO2 excess and distance-running performance. Six male endurance runners, aged 19–22 years, were subjects. Maximal oxygen uptake (VO2max), oxygen uptake (VO2) at anaerobic threshold (AT), CO2 excess and blood lactate concentration were measured during incremental exercise on a cycle ergometer and 12-min exhausting running performance (12-min ERP) was also measured on the track before and after endurance training. The absolute magnitudes in the improvement due to training for C02 excess per unit of body mass per unit of blood lactate accumulation (Ala−) in exercise (CO2 excess·mass−1·Δla−), 12-min ERP, VO2 at AT (AT-VO2) and VO2max on average were 0.8 ml·kg−1·l−1·mmol−1, 97.8m, 4.4 ml·kg−1· min−1 and 7.3 ml·kg−1·min−1, respectively. The percentage change in CO2 excess·mass−1·Δla− (15.7%) was almost same as those of VO2max (13.7%) and AT-VO2 (13.2%). It was found to be a high correlation between the absolute amount of change in CO2 excess·mass−1·Δla− and the absolute amount of change in AT-VO2 (r=0.94, P