eng Science and Education Publishing American Journal of Sports Science and Medicine 2333-4606 2021-12-16 9 1 13 23 10.12691/ajssm-9-1-4 AJSSM2021914 article Janel Bailey Janel_Bailey@yahoo.com 1 Rachel Irving 1 Paula Dawson 2 Dialo-Rudolph Brown 2 Eon Campbell 2 Department of Basic Medical Sciences, Biochemistry Section, University of the West Indies, Mona, St. Andrew, Jamaica Department of Surgery, University of the West Indies, Mona, St. Andrew, Jamaica This study aimed to investigate the influence of testosterone (T) and cortisol (C) on Skeletal Muscle Markers (SMM) at each phase of a track and field macrocycle. On a secondary basis, we also sought to determine whether C or T moderates the relationship between SMM and performance. Twenty-eighth (28) elite junior sprint athletes (15.48 ±1.89 years), and 13 non-athletic (16.15 ±1.51 years), age and gender-matched controls participated in this study. Isometric muscle strength (MS) and muscle thickness (MTH) were considered SMM. Salivary C and T levels, MS and MTH were collected between 2:30 and 3:00 p.m. before training sessions, twice during the preparatory phase [baseline (T1) and midway into the specific preparation period (T2)] and twice in competition phase [midway point of pre-competition (T3) and midway of the major competition period (T4)]. Performance data were collected during the competition phase only. No significant improvements in SMM were observed. T and T/C ratio significantly increased (p<0.05) across the season, while C levels increased relative to baseline only. While T levels did not significantly predict SMM at any phase, C levels significantly explained (p<0.05) a 60% and 74% variance in MTH and performance respectively. However, neither C nor T significantly moderated the relationship between SMM and performance. These findings suggest that raising T levels across a season may be more indicative of a response to training load, rather than a reflection of skeletal muscle adaptation. While training-induced C, which was demonstrated to have a greater influence on SMM is more sensitive to muscle function changes and performance compared to testosterone. http://pubs.sciepub.com/ajssm/9/1/4/ajssm-9-1-4.pdf testosterone cortisol skeletal muscle hormones performance macrocycle junior athletes sprint muscle adaptation