ARTICLE Explosive sport training and torque kinetics in children Raffy Dotan, Cameron J. Mitchell, Rotem Cohen, David Gabriel, Panagiota Klentrou, and Bareket Falk Abstract: A high rate of force development (RFD) is often more important than maximal force in daily and sports activities. In children, resistance training has been shown to increase maximal force. It is unclear whether, or to what extent, can children improve RFD and force kinetics. For this study, we compared strength and force kinetics of boy gymnasts with those of untrained boys and untrained men. Eight boy gymnasts (age, 9.5 ± 1.2 y), 20 untrained boys (age, 10.1 ± 1.3 y), and 20 untrained men (age, 22.9 ± 4.4 y) performed maximal, explosive, isometric elbow flexions (EF) and knee flexions (KF). Peak torque (maximal voluntary contraction (MVC)), elapsed times to 10%–100% MVC, peak rate of torque development (RTD pk ), and other kinetics parameters were determined. When gymnasts were compared with untrained boys, size-normalized EF MVC was 11%–20% higher, RTD pk was 32% higher, and times to 30% and 80% MVC were 16% and 55% shorter, respectively (p < 0.05). No corresponding differences were observed in KF. Furthermore, although the normalized EF MVC was 28% lower in gymnasts than in men (p < 0.001), their torque kinetics parameters were similar. These findings highlight the specificity of gymnastics training, which markedly elevated the torque kinetics of young, prepubertal boys to adult levels, but only moderately affected peak torque. It is suggested that neurologic adaptations, such as enhanced firing and activation rates or increased type II motor-unit recruitment, as well as changes in musculotendinous stiffness, could explain these findings. Key words: boys, exercise, gymnastics, force, muscle, strength, rate of force development. Résumé : La production rapide de force (RFD) est souvent plus importante que la force maximale dans les activités de tous les jours et dans les activités sportives. D'après la documentation scientifique, l'entraînement contre résistance améliore la force maximale chez les enfants. Il n'est pas bien établi si les enfants peuvent améliorer la RFD ou jusqu'a ` quel point c'est possible et, de plus, s'ils peuvent modifier la cinétique de la production de force. Cette étude se propose de comparer la force musculaire et la cinétique de la production de force de gymnastes a ` celles de garçons et d'hommes non entraînés. Huit jeunes gymnastes masculins, 20 jeunes garçons non entraînés et 20 hommes âgés respectivement de 9,5 ± 1,2, 10,1 ± 1,3 et 22,9 ± 4,4 ans effectuent rapidement des flexions isométriques maximales du coude (EF) et du genou (KF). On évalue le moment de force de pointe (MVC), le temps écoulé de 10 a ` 100 % MVC, le taux maximal de production du moment de force (RTD pk ) et d'autres variables de la cinétique. Le MVC-EF des gymnastes normalisé en fonction des dimensions corporelles est de 11–20 % plus élevé, le RTD pk est de 32 % plus élevé et le temps écoulé jusqu'a ` 30 % et 80 % du MVC est respectivement de 16 % et 55 % plus court comparativement aux garçons non entraînés (p < 0,05). On n'observe pas de différences correspondantes au sujet des KF. En outre, même si le MVC-EF normalisé des gymnastes est de 28 % inférieur a ` celle des hommes (p < 0,001), leur cinétique du moment de force est similaire. Ces observations soulignent la spécificité de l'entraînement a ` la gymnastique : la cinétique du moment de force chez les jeunes garçons prépubères est améliorée jusqu'aux valeurs de l'adulte, mais le moment de force de pointe n'est que moyennement modifié. Selon nous, ces adaptations sous-tendent des adaptations nerveuses telles que l'amélioration de la fréquence et de l'activation des potentiels d'action ou une plus grande sollicitation des unités motrices de type II ainsi que des modifications de la raideur musculotendineuse. [Traduit par la Rédaction] Mots-clés : garçon, exercice physique, gymnastique, force, muscle, force musculaire, taux de production de la force. Introduction High maximal strength is widely considered an important com- ponent of fitness and an essential element in many sports and occupations. Often, however, the “pattern” of force production, particularly during explosive movements, is equally, if not more, important. For example, the rate of force development, rather than one's maximal force, might be more instrumental in tasks such as jumping, running, or even lifting. Compared with adults, children have been shown to produce lower rates of torque devel- opment (RTD), not only in absolute terms, but also after their lower maximal torque has been accounted for and corrected for (Cohen et al. 2010; Falk et al. 2009a, 2009b; Mitchell et al. 2011). In adults, it has been shown that although typical resistance training increases maximal strength, it does not always improve RTD (see, for example, Andersen et al. 2010; Hakkinen et al. 1985). Andersen et al. (2010) even showed that, when normalized to max- imal voluntary contraction (MVC), peak RTD (RTD pk ) actually de- teriorated after conventional resistance training. Improved rates of torque and (or) force development are apparently achieved only or largely with specific training that stresses contractile explosive- ness or speed. The latter presumably increases motor-unit (MU) firing rates, resulting in faster activation of all recruited MUs (Duchateau et al. 2006; Gabriel et al. 2001, 2006). It could also involve greater recruitment of the fast-contracting type II MUs. In adults, improved kinetics after such training may (Barry et al. 2005) or may not (Gruber and Gollhofer 2004) be accompanied by strength gains. Thus, different mechanisms are likely responsible for improving peak torque and torque kinetics. Received 24 August 2012. Accepted 15 January 2013. R. Dotan. Faculty of Applied Health Sciences, Brock University, 500 Glenridge Ave., St. Catharines, ON L2S 3A1, Canada. C.J. Mitchell. Department of Kinesiology, McMaster University, Hamilton, ON L8S 4L8, Canada. R. Cohen. Ribstein Center for Sports Medicine and Research, Wingate Institute, Netanya, Israel. D. Gabriel, P. Klentrou, and B. Falk. Faculty of Applied Health Sciences, Brock University, 500 Glenridge Ave., St. Catharines, ON L2S 3A1, Canada; Department of Kinesiology, Brock University, St. Catharines, ON L2S 3A1, Canada. Corresponding author: Raffy Dotan (e-mail: rdotan@brocku.ca). 740 Appl. Physiol. Nutr. Metab. 38: 740–745 (2013) dx.doi.org/10.1139/apnm-2012-0330 Published at www.nrcresearchpress.com/apnm on 29 January 2013. Appl. Physiol. Nutr. Metab. Downloaded from www.nrcresearchpress.com by Brock University on 09/16/13 For personal use only.