Association Between Endogenous Testosterone With Physical Fitness Among Us Male Career Firefighters

Firefighting is a physically demanding profession associated with an unacceptably high on-duty cardiovascular (CV) mortality. Low endogenous total testosterone (TT) is an emerging cardiometabolic (CM) risk factor in men, but its interaction with physical fitness (PF) has not been explored. PURPOSE: To explore the relationship between TT and PF parameters among US male firefighters (FFs). METHODS: Data from occupational health assessments (including PF evaluations) of 301 male career FFs were analyzed. Blood samples were obtained in the morning, after 8-10 hours of fasting. TT was categorized as low (< 264 ng/dL), borderline (264–399 ng/dL), and reference (400–916 ng/dL). PF tests were performed according to the IAFC/IAFF Wellness Fitness Initiative standards, including a submaximal treadmill test, push-ups, plank, and handgrip strength. Body composition (BC) was assessed based on body fat percentage (BF%) using Jackson and Pollock 3 site skinfold formula. We compared PF within TT groups using a robust ANOVA (Welch’s F) for crude and adjusted analyses (for age and BF%). We used chi-squared test to analyze the association between low PF (<median values in each PF variable) and low TT, and calculated odds ratios (OR) to express the strength of the association. RESULTS: In crude analyses, FFs in the low TT group had worse muscular and cardiorespiratory fitness compared to the reference group. After adjusting for age and BF%, none of the PF differences remained statistically significant (Table 1). When comparing low TT vs TT reference group, less fit FFs had higher odds of having low TT considering push-ups and test duration (O.R. 2.27 - 3.24; p < 0.05). Again, when adjusting for age and BF%, none remained significant (p > 0.15). CONCLUSIONS: Our findings support the hypothesis that body fat and age mediate the relationship between TT and PF. Low TT, poor PF and BC are probably components of a complex and undesirable CM risk profile, which is especially concerning in this population. Table 1: - Adjusted comparison of physical fitness data among firefighters within different categories Low TT(<264 ng/dL) Borderline TT (264-399 ng/dL) Reference TT (400-916 ng/dL) Adj. p-value Entire Sample (n = 301) n = 32 n = 84 n = 185 * Plank1 (s) 80.5 ± 33.2 88.3 ± 41.0 86.0 ± 37.8 0.62 Push ups1 (repetitions) 26.6 ± 11.9 26.3 ± 8.0 26.8 ± 10.2 0.94 Total grip strength2 (kg) 120.9 ± 22.9 119.8 ± 16.1 119.2 ± 17.6 0.87 Treadmill Test Duration3 (s) 527.0 ± 94.9 554.3 ± 97.7 546.9 ± 94.9 0.37 (FEMA), Grant/Award Number: EMW – 2017 – FP – 00445; PPGEF – Edital 18/2023 – Programa de Pós-Graduação em Educação Física da Universidade de Brasília