Comparison of a 10 weeks resistance strength training program on prepubescent girls and boys

The mechanisms that are behind the strength gains, in strength training programs, are not still well evidenced. It seems to exist the certainty that strength training produces greater gains, during puberty and after, in virtue, over all, of the increase of serum testosterone, which allows an increase of muscle hypertrophy (Kraemer and Fleck 1993). Strength gains gotten before puberty, will be resultant of neurological adaptations, such as, the improvement of inter and intra-muscle coordination and order, the synchronization, the amount of motor units recruited, and the frequency of nervous stimulus, and not so much due to hypertrophy (Ramsay et al.,1990; Ozmun et al.,1993; Falk and Mor, 1996). The purpose of this study was to investigate the effects of a 10 weeks resistance training program on the development of the maximal isometric strength, muscle thickness, contracted brachial perimeters, relaxed brachial perimeters, the push-ups, the pull-ups and throwing a roller-skate hockey ball in prepusbescents girls and boy. Methods: The sample was divided into two different groups, the experimental one (EG, n =17) and the control one (CG, n = 17) and comprises 20 girls (9,44 ± 0,28 years) and 15 boys (9,34 ± 0,30 years) in the maturation stage I according to Tanner’s Scale. The EG group was submitted to a training program with callisthenic exercises three times a week (90 minutes each session) during 10 weeks. The program consisted of training push-ups, modified pull-ups and 2 exercises with elastics (elbows flexion and extension and extension of the arms above the head) until exhaustion. The training volume was gradually adapted from 3 series between the 1st and 3rd week to 4 series between the 4th and 6th week and to 5 series between 7th and 10th week. The maximal voluntary isometric force (MVIF) and the Electromyography signal (EMG) were acquired when the subjects made a single exercise of arm curl. To evaluate the MVIF was use a dynamometer (TSD121C from Biopac Systens Inc.). During the arm curl exercise, one surface electrode (TSD 150A from Biopac System Inc.) was attached in each biceps (MVIFARM). Ground electrode was attached to the elbow. The EMG signals were amplified by a differential amplifier with 2MW, a gain of 1000 and a bandwidth between 15-450Hz. The EMG signals were full-wave rectified and smoothed, allowing to determinate the integral of the EMG signal (iEMG) of right bicep (ARMR) and left bicep (ARML). The iEMG was relativizated according to the duration of the contraction. The muscle thicknesses of the biceps right arm (THICKBR) and left arm (THICKBL); the muscle thicknesses of triceps right arm (THICKTR) and left arm (THICKTL); the triceps skin folds of right arm (SKINTR) and left arm (SKINTL), were measured by B-mode ultrasonography, using real-time electronic scanner with 7.5MHz scanning head (Ecocamera Aloca SSD-500). The right relaxed brachial perimeters (RBPR) and left (RBPL) and the right contracted brachial perimeters (CBPR) and left (CBPL) were measured using the usual anthropometric procedures. We also evaluated the maximal number of push ups (PUSHUP) and modified pull ups (PULLUP) that each child was able to execute. Finally we measured the distance covered by the roller-skate hockey ball after being thrown (THRW). The change between the daily pay-test and after-test in such a way in boys as in girls was analyzed in both groups through the test of Wilcoxon. p≤0,05). Results: In the Wilcoxons’ test the following results had shown that the parameters with significant alterations were: in the male gender EG [(RBPR, p≤0,04; RBPL; p≤0,04; CBPR, p≤0,03; CBPL, p≤0,04; PUSHUP, p≤0,03; PULLUP, 0,03; THRW, p≤0,03)] in the CG [(RBPR, p≤0,71; RBPL; p≤0,74; CBPR, p≤0,89; CBPL, p≤0,58; PUSHUP, p≤0,83; PULLUP, 0,28; THRW, p≤0,50)] and the female EG [(RBPR, p≤0,01; RBPL; p≤0,04; CBPR, p≤0,00; CBPL, p≤0,01; PUSHUP, p≤0,00; PULLUP, 0,00; THRW, p≤0,02)] in the CG [(RBPR, p≤0,11; RBPL; p≤0,07; CBPR, p≤0,03; CBPL, p≤0,07; PUSHUP, p≤0,06; PULLUP, 0,78; THRW, p≤0,09)]. Discussion/Conclusion: The results suggested that prepubescent children can increase strength following a strength training program that includes callisthenic exercises. This training program does not seem to have a significant effect in the development of the FIMV. The strength gains were not followed by an increase of muscle mass. In this study we only evaluated the neuromuscular factors (EMG) in FIMV and the alterations of the neuromuscular activations, were not significant. It seems that the elements underlying the increase and strength gains can be related to the increase of the coordination of the movement. The coordination seems to be an element that highly contributes to the increase of strength for more complex exercises.