Abstract
INTRODUCTION: High-intensity exercises with substantial mechanical demands can contribute to greater muscular loading, potentially increasing fatigue and potentially increasing fatigue and requiring careful load-management for preventing injury and enhancing recovery planning. This study aimed to compare the effects of 2v2, 4v4, and 6v6 small-sided games (SSG) formats on muscle stiffness, creatine kinase levels, and reactive strength index (RSI) immediately post-exercise and 24 hours thereafter. METHODS: A randomized crossover design evaluated 36 male under-23 players from two regional-level amateur football teams. Participants completed 2v2, 4v4, and 6v6 over three weeks in a counterbalanced sequence, with assessments at baseline, immediately after, and 24 hours post-session. Rating of perceived exertion (RPE) was always assessed after SSGs, while muscle stiffness, creatine kinase and RSI were measured in all the time points. RESULTS: Muscle stiffness was higher in 2v2 than 4v4 (MD = 21.722, p < .001) and 6v6 (MD = 19.514, p = .002) at 24h (F = 9.346, p < .001, ηp(2) = .151). Creatine kinase was greater in 2v2 across both time points (all p < .001), while RSI was lowest in 2v2 (F = 29.313, p < .001, ηp(2) = .358). RPE was significantly highest in 2v2 (F = 42.490, p < .001), and showed strong correlations with CK (r > .63, p < .001), moderate with stiffness (r = .314), and negative with RSI (r = -.344, p < .001). CONCLUSIONS: The results suggest that 2v2 games lead to significantly higher muscle stiffness and perceived exertion, while eliciting higher CK levels and lower RSI compared to 4v4 and 6v6 formats. This suggests that small-sided games impose greater neuromuscular and muscular stress, likely due to the higher intensity typical of these formats. Coaches may therefore consider these demands when managing training loads and when planning recovery to potentially reduce excessive residual fatigue and support readiness.