Rate of Muscle Activation in Power- and Endurance-Trained Boys

Previous studies in adults have demonstrated power athletes as having greater muscle force and muscle activation than nonathletes. Findings on endurance athletes are scarce and inconsistent. No comparable data on child athletes exist. Purpose: This study compared peak torque (Tq), peak rate of torque development (RTD), and rate of muscle activation (EMG rise, Q(30)), in isometric knee extension (KE) and flexion (KF), in pre- and early-pubertal power- and endurance-trained boys vs minimally active nonathletes. Methods: Nine gymnasts, 12 swimmers, and 18 nonathletes (7-12 y), performed fast, maximal isometric KE and KF. Values for Tq, RID, electromechanical delay (EMD), and Q(30) were calculated from averaged torque and surface EMG traces. Results: No group differences were observed in Tq, normalized for muscle cross-sectional area. The Tq-normalized KE RTD was highest in power athletes (6.2 +/- 1.9, 4.7 +/- 1.2, 5.0 +/- 1.5 N.m.s(-1), for power, endurance, and nonathletes, respectively), whereas no group differences were observed for KF. The KE Q(30) was significantly greater in power athletes, both in absolute terms and relative to peak EMG amplitude (9.8 +/- 7.0, 5.9 +/- 4.2, 4.4 +/- 2.2 mV.ms and 1.7 +/- 0.8, 1.1 +/- 0.6, 0.9 +/- 0.5 (mV.ms)/(mV) for power, endurance, and nonathletes, respectively), with no group differences in KF. The KE EMD tended to be shorter (P = .07) in power athletes during KE (71.0 +/- 24.1, 87.8 +/- 18.0, 88.4 +/- 27.8 ms, for power, endurance, and nonathletes), with no group differences in KF. Conclusions: Pre- and early-pubertal power athletes have enhanced rate of muscle activation in specifically trained muscles compared with controls or endurance athletes, suggesting that specific training can result in muscle activation-pattern changes before the onset of puberty.