Postexercise heart rate recovery in children: relationship with power output, blood pH, and lactate.

The aim of the present study was to determine whether differences in age-related heart rate recovery (HRR) kinetics were associated with differences in power output, blood lactate concentration ([La]b), and acidosis among children, adolescents, and adults. Ten prepubertal boys (aged 9.6 +/- 0.7 years), 6 pubertal boys (aged 15.2 +/- 0.8 years), and 7 men (aged 20.4 +/- 1.0 years) performed 10 repeated 10-s all-out cycling sprints, interspersed with 5-min passive recovery intervals. Mean power output (MPO) was measured during each sprint, and HRR, [La]b, and acidosis (pHb) were determined immediately after each sprint. Children displayed a shorter time constant of the primary component of HRR than adolescents and adults (17.5 +/- 4.1 vs. 38.0 +/- 5.3 and 36.9 +/- 4.9 s, p < 0.001 for both), but no difference was observed between adolescents and adults (p = 1.00). MPO, [La]b, and pHb were also lower in children compared with the other 2 groups (p < 0.001 for both). When data were pooled, HRR was significantly correlated with MPO (r = 0.48, p < 0.001), [La]b (r = 0.58, p < 0.001), and pHb (r = -0.60, p < 0.001). Covarying for MPO, [La]b, or pHb abolished the between-group differences in HRR (p = 0.42, p = 0.19, and p = 0.16, respectively). Anaerobic glycolytic contribution and power output explained a significant portion of the HRR variance following high-intensity intermittent exercise. The faster HRR kinetic observed in children appears to be related, at least in part, to their lower work rate and inherent lack of anaerobic metabolic capacity.