Acute changes in gastrocnemius muscle stiffness following different work–rest calf-raise protocols and percussive therapy

Background: Work–rest (W:R) structure is a key programming variable in athletic training. This randomized crossover experimental study examined how 3 calf-raise W:R configurations affected acute medial gastrocnemius stiffness measured by shear-wave elastography (SWE), and how stiffness changed during a standardized percussive therapy (PT) recovery period. Methods: Thirty trained volleyball athletes (15 women, 15 men) completed 3 randomized sessions: 30 s work/30 s rest (30–30), 15 s work/45 s rest (15-45), and 45 s work/15 s rest (45-15). This randomized 3-period crossover experimental study was designed and reported in accordance with the CONSORT 2010 Statement and its extension for randomized crossover trials. SWE was measured at baseline (Pre), immediately postexercise (Acute), and after a 5-minute PT period (Post). Repeated-measures analysis of variance tested Time and Protocol effects; estimated marginal means, 95% confidence intervals (CIs), and within-protocol contrasts were reported. Limb side and sex were examined cautiously as exploratory factors. Results: A significant Time effect ( F [2,58] = 51.51, P < .001, η p 2 = 0.64) and Time × Protocol interaction ( F [4116] = 7.16, P < .001, η p 2 = 0.20) were observed. Acute increases were largest in 45-15 (+0.22 m/s, 95% CI: 0.20–0.24), followed by 30-30 (+0.15 m/s, 95% CI: 0.10–0.20) and 15-45 (+0.08 m/s, 95% CI: 0.05–0.12). Stiffness decreased from Acute to Post in all protocols, with the largest reduction in 45-15 (−0.32 m/s, 95% CI: −0.40 to −0.24). Conclusion: Work density altered acute gastrocnemius SWE responses, with the highest-density 45-15 protocol producing the largest stiffness increase. Stiffness returned toward baseline during the postexercise PT recovery period; however, because no sham or passive recovery condition was included, PT-specific effects cannot be isolated from spontaneous recovery.