DOTAN, R., B. FALK, and A. RAZ. Intensity effect of active recovery from glycolytic exercise on decreasing blood lactate concentration in prepubertal children. Med. Sci. Sports Exerc., Vol. 32, No. 3, pp. 564–570, 2000.
Purpose: Children’s performance after intense exercise is known to recover faster than that of adults. However, very little is known about the physiological processes that differentiate children from adults in their recovery. The purpose of this study was to compare, in children, the decrease in blood lactate concentration ([La]) during various intensities of active recovery from highly intense exercise with that during passive recovery.
Methods: Subjects were 15 healthy, physically active, prepubertal, 9- to 11-yr-old boys (N = 8) and girls (N = 7). Subjects performed three 40-s cycling bouts at 150% peak oxygen consumption (V̇O2peak), with two 50-s rest intervals, followed by 2 min of passive recovery and 23 min of one of four randomly-assigned recovery levels: passive and 40%, 50%, and 60% V̇O2peak (RP, R40, R50, and R60, respectively).
Results: Mean values of peak [La] (by treatment) ranged between 9.9 ± 1.5 and 10.8 ± 2.0. Whereas HR and V̇O2 remained relatively higher, [La] decreased faster during all active recoveries compared with the passive mode. [La] during R60 was higher compared with [La] during R40. [La] was slightly higher in the first 10 min of R40 compared with R50, whereas from the 15th min onward, this difference was reversed. A similar pattern was seen in the boys and girls, separately. The calculated half-life of [La] was significantly higher during the passive compared with all three active recoveries, with no differences among the latter (22.0 ± 5.0, 10.3 ± 1.9, 10.5 ± 2.2, and 11.5 ± 2.1 min during RP, R40, R50, and R60, respectively).
Conclusions: In summary, similar to the case in adults, the decrease in [La] after intense exercise in children is faster during active recovery compared with the passive mode. Further research is required to determine whether performance recovery parallels that of [La] in children and adults of both genders.
Children’s play and sport activities are often intermittent and performed at fairly high intensities (2). Furthermore, the increasing involvement of children in intense, competitive sports, adds both practical and physiological relevance to the understanding of their responses to and recovery from intense exercise. Although the recovery from intense exercise is known to be faster in children than in adults (22), very little experimental data exist concerning the physiological processes that differentiate the two age groups.
It has been widely demonstrated in adults that lactate (La) accumulation is closely associated with muscle fatigue and endurance, as well as with the rate of recovery of dynamic exercise performance (27,28,38,47). The relationship between [La] and subsequent performance is complex and has not so far been fully elucidated. Nevertheless, the relevance of elevated recovery [La] to compromised subsequent performance—likely due to the inverse relationship of La to pH (11,43), as well as to its own direct influence (18,25)—has been shown in many studies (19,28,38,47). Thus, accelerated [La] reduction after intense exercise could be advantageous in adults, and presumably also in children.
[La]peak after maximal and supramaximal exercise in children is characteristically lower than in adults, as is their anaerobic power output (see (46) for a review). Additionally, [La]peak observed after exercise appears sooner in children compared with adults (15,21). In a recent study (15), we found a similar La half-life (T50La) in children and adults during passive recovery from supramaximal exercise, regardless of the large differences in body mass–specific power output and [La]peak attained after the exercise task. Thus, explanations for children’s faster recovery of performance capacity include their shorter time to [La]peak from the end of exercise and, in particular, the fact that they have less to recover from. That is, they need to recover from a lower power output (26) and lower consequent [La]peak. Additional explanations for children’s faster recovery may involve physiological differences such as a shorter circulation time (12) and muscle-to-capillary diffusion distance (7), both of which may contribute to a faster decrease in both muscle and blood [La]. Enzymatic or other biochemical differences may also be part of the explanation. At present, however, such differences can neither be supported nor refuted.
In adults, [La] decrease after intensive exercise is accelerated by active recovery compared with the passive mode (5,9,14,17,31,36). This is due to the fact that, when work intensity is well below the lactate threshold (LT), La removal greatly exceeds La production. Additionally, the elevated muscle blood flow during dynamic exercise expedites La removal (8). During active recovery, [La] decrease was found to be largely dependent on the involved muscle mass and metabolic rate (below the anaerobic threshold) (3,30). Although in normal individuals, maximal removal rates may be reached at recovery intensities above 60% V̇O2peak (23), the suggested recovery intensity for adults is 30–45% V̇O2peak (13,14) because [La] production is much lower than its removal at the latter intensity.
In children, it has not been established whether active recovery is preferential to the passive mode in decreasing postexertion [La] as is the case with adults, and if so, what is its optimal intensity. There are several known differences between children and adults that suggest that children’s optimal recovery intensity would be higher than that recommended for adults: a) the activity of muscle phosphofructokinase is known to be lower in children compared with adults (16); b) even at similar body mass–corrected power outputs, children display a lower blood [La] (15); c) children’s LT occurs at a higher percentage of V̇O2peak than that of adults (33,34,46). These differences suggest that La production at a given relative exercise intensity is lower in children than in adults. On the other hand, there is no evidence to suggest that La removal is different between children and adults. Therefore, at a given active recovery intensity, the reduction in [La] may be greater in children than in adults. It stands to reason, therefore, that children should benefit from active recovery, and that their optimal recovery intensity would be higher than in adults. The purpose of the present study was to investigate children’s [La] dynamics at various intensities of active recovery compared with the passive mode.