IS CHILDREN’S FASTER RECOVERY FROM EXERCISE DUE TO A HIGHER METABOLITE CLEARANCE RATE?

Dear Editor-in-Chief: We are writing regarding a recent article by Zafeiridis et al. (5), comparing recovery from high-intensity exercise in boys, adolescents, and adults. A faster recovery of performance capacity (knee flexion/extension) was demonstrated in children and adolescents compared with adults. It was concluded that recovery rate was maturity dependent. While the study and its results are well presented, we believe there is a significant discussion oversight regarding the mechanisms underlying this phenomenon. The authors speculate that a possible explanation may be a higher metabolite (lactate, H+) clearance rate in children: “Based on these facts, the possibility that the boys and teens in the current study had faster removal of lactate that facilitated the recovery process should not be excluded” (p. 511). The authors failed to consider the experimental evidence that contradicts their explanation. We addressed this very issue in a paper by Dotan et al. (1), which demonstrated, that blood lactate (La) disappearance rate following high-intensity exercise, is strikingly similar in children and adults, despite markedly different peak values ([La]peak). It was shown that not only was children’s La-disappearance half-time similar to that of adults, but that there was no difference between their La-recovery curves following similar [La]peak values. The only consistent difference being children’s shorter lag time to [La]peak. Therefore, it was argued that faster recovery in children is not due to a more efficient metabolite clearance rate, but rather to the fact that they have less to recover from (lower power output and La production) and that their [La]peak is reached sooner. The evidence of children’s lower sympathetic activation (3) that Zafeiridis et al. (5) cite in support of their view only supports our notion that children are anaerobically inferior, precisely because they are unable to fully mobilize their sympathetic system and recruit higher hierarchy motor units. This would explain their lower La production but not a faster La clearance. This is not to exclude other factors that separate boys from men (e.g., faster phosphocreatine resynthesis (2,4)). However, future research may well demonstrate that many or all of these differences stem from the alleged maturation-related difference in recruitment potential. Bareket Falk Raffy Dotan Brock University, Department of Physical Education and Kinesiology, St. Catharines, Ontario, Canada

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