Purpose: The purpose of the study was to determine if measured maximal heart rate (HRmax) was affected by gender or aerobic training status, as well as to determine the accuracy of three common clinical maximal heart rate regression equations (MHREs) used to predict HRmax: HRmax = 220 – age, HRmax = 226 – age, & HRmax = 208 – (0.7 ∙ age). Methods: Fifty-two aerobically active males (N=15) and females (N=15), and sedentary males (N=9) and females (N=13) within an age range of 18-25 years and with a normal BMI (18.5-24.9 kg∙m-2) underwent a Bruce maximal treadmill exercise protocol. Heart rate, oxygen consumption (VO2), and respiratory exchange ratio (RER) were measured. The effect of gender and training status on HRmax was analyzed through a two-way ANOVA, and the effect of gender, aerobic training status, and regression equation on accuracy of the HRmax prediction was assessed with a threeway ANOVA (α=0.05). The dependent variables for the three-way ANOVA included both signed residuals (observed HRmax – predicted HRmax) and unsigned residuals [absolute value of (observed HRmax – predicted HRmax)]. Results: Males and sedentary individuals had higher measured HRmax (p<.001 and p=.002, respectively) than females and active individuals. The prediction equation HRmax = 208 – (0.7 ∙ age) had the lowest marginal error under the signed residuals (p = 0.000). When looking at the unsigned residuals, the best overall equation, equation for females, and equation for the active under the unsigned residuals was HRmax = 208 – (0.7 ∙ age) (p = 0.000). However, the best equation for males and those that are sedentary under the unsigned residuals was HRmax = 220 – age. Conclusion: Despite small differences, HRmax = 208 – (0.7 ∙ age) was the best overall equation to use for the greatest accuracy.