Association of Endogenous Testosterone with Physical Fitness Measures during Firefighter Occupational Health Evaluations

Abstract

Firefighting is a physically demanding profession associated with unacceptably high on-duty cardiovascular mortality. Low endogenous total testosterone (TT) is an emerging cardiometabolic (CM) risk factor in men, but limited data exists on its interactions with physical fitness (PF). Data from occupational health and fitness assessments of 301 male career firefighters (FFs) were analyzed. TT was categorized as low (<264 ng/dL), borderline (264-399 ng/dL), and reference (400-916 ng/dL). PF tests included cardiorespiratory fitness (submaximal treadmill), body fat percentage (BF%), push-ups, plank, and handgrip strength assessments. In the crude analyses, FFs in the low TT group had worse muscular and cardiorespiratory fitness measures compared to the referent group. However, after adjusting for age and BF%, none of the PF differences remained statistically significant. Similarly, the odds of less-fit FFs (PF performance below median values) having low TT were higher compared to the fitter ones only before adjusting for age and BF%. Therefore, in the final adjusted model, there was no significant association between TT and PF. Our data suggest that age and body fat confound the association between PF and TT. Low TT and poor PF are important components of FFs' CM risk profile, and there is potential benefit to considering TT screening as part of a comprehensive occupational health program that manages performing medical evaluations and provides education and preventative programming.

Keywords: cardiometabolic; cardiovascular; public safety; risk; workforce.

Figure 1

The association between having low fitness values (≤median values) and having low total testosterone (<264 ng/dL). The reference groups for each physical fitness test are composed of individuals who performed better than the median value of the sample; e.g., those with a shorter Bruce treadmill test duration were at higher odds of having low testosterone compared to those with longer test durations in the crude analysis. The adjusted analysis includes age and body fat percentage values as covariates. (A): Analysis including the entire sample; (B): Analysis including only the low total testosterone and reference range (400–916 ng/dL) groups; *: Significant association with p < 0.05.

Figure 2

The strength of the association between having one of two different cardiometabolic risk factors (age ≥ 45 years or obesity) and having low total testosterone (<264 ng/dL). For the age risk factor, the reference is the firefighters < 45 years old. For the obesity risk factors, the reference is the firefighters without obesity. The adjusted analysis for the obesity odds ratio included age, while the adjusted analysis for age ≥ 45 years odds ratio used body fat percentage. (A): Analysis including the entire sample; (B): Analysis including only the low total testosterone and reference range (400–916 ng/dL) groups; *: Significant association with p < 0.05.