Michaelides, MA, Parpa, KM, Henry, LJ, Thompson, GB, and Brown, BS. Assessment of physical fitness aspects and their relationship to firefighters' job abilities. J Strength Cond Res 25(4): 956-965, 2011-The purpose of this study was to identify the relationships between various fitness parameters and firefighting performance on an “Ability Test” (AT) that included a set of 6 simulated firefighting tasks. The relationships between each fitness parameter and each task of the AT were determined. Ninety firefighters participated in this study (age 33 ± 7 years). The AT completion time was associated with abdominal strength (r = −0.53, p < 0.01), relative power (r = −0.44, p < 0.01), upper-body muscular endurance (push-ups, r = −0.27, p < 0.05) (sit-ups, r = −0.41, p < 0.01), and upper-body strength (1 repetition maximum bench press, r = −0.41, p < 0.01). In addition, poor performance on the AT was associated with high resting heart rate (r = 0.36, p < 0.01), high body mass index (r = 0.34, p < 0.01), high body fat (BF)% (r = 0.57, p < 0.01), increasing age (r = 0.42, p < 0.01), and large waist size (r = 0.67, p < 0.01). Multiple regression analyses indicated that a significant (F[5, 53] = 14.02, p < 0.01) proportion (60%) of the variation observed in the AT was explained by the variation of the fitness parameters used in the model. This study demonstrated that fitness variables, such as abdominal strength, power (step test), push-ups, resting Hr, and BF%, contributed significantly to the predictive power of firefighters' AT performance. The findings of this study may be useful to fire department instructors and trainers in the design and implementation of training programs that are more specifically tailored to improving both individual firefighting skills and general fire suppression performance.