Contralateral repeated bout effect in the triceps surae after unilateral heel drop exercise at 2- and 7-day interbout intervals.

PURPOSE: A single bout of unaccustomed eccentric exercise can protect against subsequent strength loss and soreness, with protection sometimes transferring to the unexercised contralateral limb. The contralateral repeated bout effect (CL-RBE) may be relevant for muscle-tendon units with comparatively small fascicle strains during eccentric tasks, such as the triceps surae, but has not been established in this muscle group. We tested whether unilateral eccentric heel drops produced evidence consistent with the CL-RBE in the triceps surae and whether its expression differed after 2- and 7-day interbout intervals. METHODS: Twenty-four participants completed 225 unilateral eccentric heel drops (ECC1), then repeated the task on the opposite limb (ECC2) after 2 days (2D, n=12) or 7 days (7D, n=12). Maximal voluntary isometric plantar-flexor torque (MVIC) and soreness were assessed at baseline (PRE) and post-exercise. Surface electromyography (sEMG) amplitude (root mean square, RMS) and median frequency (MDF) were quantified during each bout. RESULTS: At 48 h, normalised MVIC torque was higher after ECC2 than ECC1 in 2D (10.8%PRE, 95% CI 3.0-18.5%PRE) and 7D (12.6%PRE, 95% CI 4.6-20.6%PRE), with no evidence that the ECC2-ECC1 torque response differed between intervals. Soreness was lower after ECC2 only in 2D (- 3.83/60, 95% CI -6.62 to -1.05). sEMG RMS and MDF showed no muscle-specific or interval-dependent bout effects. CONCLUSION: Unilateral eccentric heel drops produced evidence consistent with the CL-RBE in the triceps surae, expressed as reduced contralateral strength loss across 2- and 7-day intervals. Soreness attenuation was less consistent, while sEMG indices remained unchanged.