Effects of two plyometric protocols at different surfaces on mechanical properties of achilles tendon in children

Abstract

Objectives: The purpose of this study was to compare the changes in muscle strength and Achilles tendon strain after two plyometric training programs performed on different surfaces in children. Methods: Thirty six children (21 girls, 15 boys) aged 9.30_0.55 years were assigned into a mini-trampoline plyometric group (TPLG), a ground-plyometric group (GPLG) and a control group (CG). The training groups completed a 4-week plyometric intervention (PL) (three-times a week), consisting of hopping exercises performed either on a mini-trampoline (TPLG) or ground (GPLG). Achilles tendon strain, peak ankle plantar flexion torque (PAT), and rate of torque development (RTD) at 3 different angular positions of the ankle (15°, 0° and -15°) were measured before and after training. Results: The main finding of this study was that Achilles tendon strain decreased significantly after plyometric training performed on a mini-trampoline or ground surface (25% and 15%, for the TPLG and GPLG, respectively (P < 0.05). This was accompanied by an increase in maximum ankle MVC torque and an increase in RTD (at 15°, 0° positions) for both experimental groups. Especially, statistically significant increases in PAT (30%) and RTD (14%) (P < 0.05) were found for the TPLG while for the GPLG group the increase was 19 % and 8% for PAT and RTD, respectively (P < 0.05). Conclusions: Both protocols show similar adaptations regardless of the surface of training. Training on elastic surface should be incorporated into exercise programs aiming either to enhance strength performance safely, or to achieve the target goal which is not only the safe performance but also the muscle-tendon system efficiency.