Blood lactate and pyruvate concentrations, and their ratio during exercise in healthy children: developmental perspective.

Blood concentrations of lactate normally increase during and after intense exercise as does the ratio of concentrations of lactate to pyruvate (L:P). Since there appear to be differences in blood lactate concentrations on exercise, in muscle metabolic enzyme activities, and in anaerobic capacity between children and adults, we speculated that there would be age related differences in lactate and pyruvate concentrations, and their ratio among children. Whole blood concentrations of lactate and pyruvate were measured in 28 healthy children aged 7-17 years, split into three age groups: less than 11, 11-14, and 15-17 years. Blood was drawn at rest, immediately after 6 min of exercise at one-third and two-thirds of maximum work capacity (Wmax), and 20 min after completion of work. Lactate and pyruvate concentrations increased significantly from rest to exercise at two-thirds Wmax [approximately 72% of peak oxygen consumption (VO2peak)]. Whereas greater increments in lactate concentration were seen with groups of increasing age, exercise-related increments in pyruvate concentrations were no different among age groups. There was a significant rise in L:P ratio on exercise, with greater increments found from the youngest to the oldest group. There were no sex differences. We concluded that in healthy children exercising at approximately 70% of VO2peak there is a rise in blood lactate concentration in excess of that of pyruvate, such that the L:P ratio rises to a degree determined by age. This suggests age dependent changes, perhaps coincident with puberty, in pathways involved in lactate production and/or elimination.