Firefighters are responsible for protecting citizens as well as the infrastructure of cities across the United States. In order to safely protect and perform on-duty tasks, firefighters must be capable of performing physiologically demanding skills. Emerging evidence has led to heightened concern for firefighters’ increased obesity levels and decreased physical activity (PA). Formal exercise and PA research specific to firefighters is lacking. More specifically, there is a lack of literature using accelerometers to objectively measure PA. There is more evidence, however, to demonstrate firefighters have a high prevalence of obesity surpassing the general population. Not only are firefighters overweight and inactive, but also they are not aerobically fit to adequately perform their job-specific tasks. Purpose: To examine the relationship of PA and obesity to cardiorespiratory fitness (CRF). Methods: Firefighters (n=29) wore an accelerometer for eight consecutive on- and off-duty days. The accelerometer was worn on the right hip and tracked sedentary activity, light physical activity (LPA), moderate physical activity (MPA), vigorous physical activity (VPA), and moderate-to-vigorous physical activity (MPVA). Additionally, each participant completed a stage-graded exercise test with submaximal square-wave verification bout to determine maximal oxygen uptake (VO2max). A stepwise linear regression model was conducted using physical activity intensity, body mass index (BMI), and waist circumference (WC) as predictor variables for CRF. Results: According to the World Health Organization BMI categorization, none were normal weight, 20 were overweight, and 9 were obese. Firefighters spent roughly 61% of their waking hours in sedentary activity, 35.4% in LPA, and only 3.6% in MVPA. The two linear regression models were used to investigate whether PA intensity, step count, physical activity rating scale, BMI, or WC were more predictive of VO2max. VPA was predictive of VO2max (F(1,27) = 7.89, R2 = 0.23, p <0.01). Additionally, when BMI and WC were added, only WC was predictive of VO2max (F(1,27) = 11.76, R2 = 0.30, p<0.01). Conclusion: It is imperative fire departments emphasize the importance of cultivating an environment where improved health and wellness is essential for firefighters to adequately perform their physiologically demanding tasks.