Changes in Resting Titin and Irisin Concentrations are Associated with Thigh Muscle Volume in National-level Sprinters: Observations After a 5-month Sprint-based Training Macrocycle

Nuell, S, Bárcena, C, Illera-Domínguez, V, Lloret, M, Padulles, JM, Cadefau, JA, and Cosio, PL. Changes in resting titin and irisin concentrations are associated with thigh muscle volume in national-level sprinters: observations after a 5-month sprint-based training macrocycle. J Strength Cond Res XX(X): 000-000, 2026-Titin and irisin are muscle-specific biomarkers that have been associated with signaling pathways mediating muscle adaptation and growth. Therefore, the purpose of the study was to analyze the effect of a sprint-based training macrocycle (SBTM) on thigh muscle volume (MV) and associated muscle-specific blood biomarkers in national-level sprinters. Healthy national-level sprinters (6 men, 6 women) completed a 5-month SBTM. Resting levels of muscle-specific biomarkers (creatine kinase, lactate dehydrogenase, titin, and irisin) along with individual thigh MVs were analyzed before and after completion of a 5-month SBTM through an ecological follow-up design. The SBTM caused an increase in resting levels of titin (9.5-64.9%, p = 0.013, g = 0.79), and irisin (24.6-46.9%, p < 0.001, g = 1.90), together with an increase in total thigh MV (6.3-13.9%, p < 0.001, g = 1.56) in male and female sprinters. In addition, increases in total thigh MV were significantly correlated with increases in titin (r = 0.80, p = 0.024) and irisin (r = 0.78, p = 0.024). A long-term sprint training program can be a useful approach to promote muscle-specific adaptations in national-level sprinters. Changes in resting levels of titin and irisin are positively correlated with increases in thigh MV, suggesting their potential role as indicators of muscle adaptation.