The effect of repeated sprints on immunological modulation and the role of fat-free mass, biological maturation and dietary inflammatory index in male athletes: A quasi-experimental study with insights for training loads control

Paulo Francisco de Almeida-Neto^1*E. Alana D. Fernandes¹Gilmara Gomes de Assis²Katsuhiko Suzuki³ROBERTO FERNANDES DA COSTA⁴Lívia de Melo Atanásio¹Felipe J. Aidar⁵BRENO Guilherme De Araujo Tinoco CABRAL^1*Paulo Moreira Silva Dantas^1*

• ¹Federal University of Rio Grande do Norte, Natal, Brazil
• ²Instituto Politecnico de Viana do Castelo, Viana do Castelo, Portugal
• ³Waseda Daigaku - Tokorozawa Campus, Tokorozawa, Japan
• ⁴Universidad Autonoma de Chile - Campus Providencia, Santiago, Chile
• ⁵Universidade Federal de Sergipe, São Cristóvão, Brazil

Abstract Background: Repeated sprint exercise (RSE) induces inflammation, which may be modulated by fat-free-mass (FFM), biological maturation (BM), and dietary patterns, assessed by the Dietary Inflammatory Index (DII). Aim: To examine the influences of FFM, BM, and DII on cytokine responses to RSE in male athletes. Methods: A study with a quasi-experimental approach and cross-sectional design with a sample of 30 male athletes (20-adolescents, 10-adults). Blood samples were collected pre-, immediately after, 2h and 24h after RSE (3-sets of 6 × 35-m sprints). IL-1β, IL-6, IL-8, and IL-10 were analyzed via flow cytometry. FFM was assessed by DXA, BM by predictive models, and DII by 24h dietary recalls. Prior exploratory analyses included Spearman's and partial correlations, and Mann-Whitney-U tests. Main analyses were conducted using Generalized-Linear-Mixed-Models (GLMM) Results: The GLMMs confirmed that BM, FFM, and DII significantly influenced cytokine responses (p<0.05). FFM emerged as a significant predictor of IL-1β (p=0.0023). For IL-6, there was a time effect (p<0.001) and a Time×BM interaction (p=0.040), with FFM and DII being significant predictors in both groups. A similar interaction was observed for IL-8 (p=0.036). For IL-10, there was a Time×BM interaction (p<0.001), where adults showed superiority over adolescents (p<0.05). Post-hoc analyses revealed that adolescents with lower FFM had a more prolonged inflammatory response (increased-IL-6), while adults with higher FFM demonstrated a more effective anti-inflammatory capacity (increased-IL-10). Conclusion: FFM, BM, and DII play key roles in shaping the inflammatory response to RSE and should be considered when prescribing training loads to optimize recovery and performance.