Influence of strength on magnitude and mechanisms of adaptation to power training

Purpose: To determine whether the magnitude of performance improvements and the mechanisms driving adaptation to ballistic power training differ between strong and weak individuals. Methods: Twenty-four men were divided into three groups on the basis of their strength level: stronger (n = 8, one-repetition maximum-to-body mass ratio (1RM/BM) = 1.97 ± 0.08), weaker (n = 8, 1RM/BM = 1.32 ± 0.14), or control (n = 8, 1RM/BM = 1.37 ± 0.13). The stronger and weaker groups trained three times per week for 10 wk. During these sessions, subjects performed maximal-effort jump squats with 0%-30% 1RM. The impact of training on athletic performance was assessed using a 2-d testing battery that involved evaluation of jump and sprint performance as well as measures of the force-velocity relationship, jumping mechanics, muscle architecture, and neural drive. Results: Both experimental groups showed significant (P ≤ 0.05) improvements in jump (stronger: peak power = 10.0 ± 5.2 W•kg, jump height = 0.07 ± 0.04 m; weaker: peak power = 9.1 ± 2.3 W•kg, jump height = 0.06 ± 0.04 m) and sprint performance after training (stronger: 40-m time =-2.2% ± 2.0%; weaker: 40-m time =-3.6% ± 2.3%). Effect size analyses revealed a tendency toward practically relevant differences existing between stronger and weaker individuals in the magnitude of improvements in jump performance (effect size: stronger: peak power = 1.55, jump height = 1.46; weaker: peak power = 1.03, jump height = 0.95) and especially after 5 wk of training (effect size: stronger: peak power = 1.60, jump height = 1.59; weaker: peak power = 0.95, jump height = 0.61). The mechanisms driving these improvements included significant (P ≤ 0.05) changes in the force-velocity relationship, jump mechanics, and neural activation, with no changes to muscle architecture observed. Conclusions: The magnitude of improvements after ballistic power training was not significantly influenced by strength level. However, the training had a tendency toward eliciting a more pronounced effect on jump performance in the stronger group. The neuromuscular and biomechanical mechanisms driving performance improvements were very similar for both strong and weak individuals