Oxygen deficit and blood lactate in prepubertal boys during exercise above the anaerobic threshold

Recent studies have shown that in boys a steady-state of blood lactate is maintained at exercise levels above the anaerobic threshold. Therefore, the explanation hitherto provided for the steeper increase in blood lactate beyond the anaerobic threshold, i.e. the onset of anaerobic metabolism, needs modification. Investigations were carried out in ten boys, aged 11-12 years, during treadmill running. Maximal oxygen uptake (VO2max) and maximal blood lactate were determined during incremental exercise. Subsequently each boy performed four runs at different high constant speeds of 16 min duration, in order to determine maximal steady-state blood lactate. The underlying data also served to estimate roughly the lactate anaerobic threshold. Oxygen uptaken (VO2) was measured at 0.5 min intervals during the initial 7.5 min of each constant-speed run. Maximal steady-state blood lactate was 5.6 mmol/l corresponding to 92% of VO2max. The mean blood lactate at which the anaerobic threshold was reached or just exceeded was 2.7 mmol/l corresponding to 82% of VO2max. Oxygen transport transient kinetics were computed from the mean 0.5 min VO2-values during the constant-speed runs near the maximal steady-state blood lactate and from runs near the anaerobic threshold. Half-times of VO2 response were shorter than values previously reported for adults due to a faster increase in VO2 at the onset of exercise. Half-times increased with increasing work rates as did the oxygen deficit, due to a slower increase in VO2 along with a longer time required to attain a steady-state at higher work rates.(ABSTRACT TRUNCATED AT 250 WORDS)