The contribution of muscle hypertrophy to strength changes following resistance training

Whilst skeletal muscle hypertrophy is considered an important adaptation to resistance training (RT), it has not previously been found to explain the inter-individual changes in strength after RT. This study investigated the contribution of hypertrophy to individual gains in isometric, isoinertial and explosive strength after 12 weeks of elbow flexor RT. Thirty-three previously untrained, healthy men (18-30 years) completed an initial 3-week period of elbow flexor RT (to facilitate neurological responses) followed by 6-week no training, and then 12-week elbow flexor RT. Unilateral elbow flexor muscle strength [isometric maximum voluntary force (iMVF), single repetition maximum (1-RM) and explosive force], muscle volume (V (m)), muscle fascicle pennation angle (theta (p)) and normalized agonist, antagonist and stabilizer sEMG were assessed pre and post 12-week RT. Percentage gains in V (m) correlated with percentage changes in iMVF (r = 0.527; P = 0.002) and 1-RM (r = 0.482; P = 0.005) but not in explosive force (r a parts per thousand currency sign 0.243; P a parts per thousand yen 0.175). Percentage changes in iMVF, 1-RM, and explosive force did not correlate with percentage changes in agonist, antagonist or stabilizer sEMG (all P > 0.05). Percentage gains in theta (p) inversely correlated with percentage changes in normalized explosive force at 150 ms after force onset (r = 0.362; P = 0.038). We have shown for the first time that muscle hypertrophy explains a significant proportion of the inter-individual variability in isometric and isoinertial strength gains following 12-week elbow flexor RT in healthy young men.