Biochemical, immune, and endocrine biomarkers associated with exacerbated muscular response: insights from a field-based operational cohort study

Muscle damage and systemic stress responses are common consequences of intense physical exertion. However, the extent to which these responses vary according to the severity of muscular strain remains unclear. We conducted a field-based study involving 24 active-duty elite military personnel who participated in five distinct operational missions in Brazil. Circulating levels of 36 plasma biomarkers were assessed and compared between individuals presenting moderate or exacerbated muscular response, defined by serum creatine kinase (CK) concentrations below or above 1000 U/L, respectively. Statistical comparisons and multivariate logistic regression were performed to evaluate associations between biomarker levels and muscular response severity. Our analysis revealed that individuals with exacerbated response exhibited distinct systemic profiles, marked by elevated tissue injury markers, reduced eosinophil and lymphocyte counts, and lower adrenal steroid hormone concentrations. Furthermore, regression models identified creatine kinase muscle-brain (CKMB) and alanine aminotransferase (ALT) as independently associated with higher CK levels, while heightened eosinophil counts showed a potential protective trend. These findings suggest that greater degrees of muscular stress are associated with broader systemic dysregulation, and that specific circulating biomarkers may serve as indicators of individual susceptibility to acute stress in high-demand physical environments.