Relationship between hypertrophy, strength gains and tensiomyography adaptations: a moderator role of contraction duration

The aim of the study was to investigate how the relationship between resistance training-induced hypertrophy, strength, and passive contractile adaptations is affected by contraction duration. Twenty university students (11 males) were randomly assigned to either the fast eccentric/fast concentric phase group (F/F; 1 s both phases) or the slow eccentric/fast concentric phase group (S/F; 4 s and 1 s, respectively). Both experimental groups completed a 7-week biceps curl training programme with a total of 14 sessions (2 days/week). Elbow flexor muscle thickness (MT), one-repetition maximum (1RM), and tensiomyographic (TMG) parameters (radial displacement-D-m and contraction time-T-c) were assessed. The percentage change ( increment ) in MT correlated significantly with the increment 1RM only in the S/F group (r = 0.712, p < 0.05). Both groups demonstrated significant negative associations between increment MT and increment D-m (r = 0.717-0.760, p < 0.01). Conversely, no significance was found between increment MT and increment T-c (F/F: r = -0.398, p = 0.255; S/F: r = 0.410, p = 0.239), increment 1RM and increment T-c (F/F: r = -0.278, p = 0.436; S/F: r = 0.223, p = 0.536), nor increment 1RM and increment D-m (F/F: r = - 0.131, p = 0.719; S/F: r = - 0.351, p = 0.320). The main findings indicate that the relationship between hypertrophy and strength gains is significantly stronger when resistance training was paced with slower eccentric contractions comparing to fast ones. On the other hand, reduced D-m values indicate increase in MT regardless of contraction duration, while strength gains are not correlated with corresponding TMG changes.