Background: Having an abnormal body mass index (BMI) adversely affects cardiac workload and level of physical activity. Objective: To examine the relationship between cardiac workload, physical activity, Sex, and BMI. Methods: The number of steps taken per day (Steps) and minutes per week spent in targeted heart rate zones were collected from primarily first and second year university students (n = 1,801; 62% female) over a standard, 15-week long semester. Other data collected included BMI, Sex, Age, and Class Standing. Sex differences in BMI, Steps, and training heart rate zone (heart rates above 50% of max) minutes (THR) were evaluated, correlations between the study parameters were analyzed, and one-way ANOVA was used to test between competing models. The values p < .05 were considered statistically significant. Results: Statistically significant (p < .05) differences between males and females were found for Steps, THR, and BMI. Males were more physically active but spent 18% less time with heart rates above 50% of max. Students who had abnormal BMI values, both low and high, experienced greater cardiac workload (p < .05), even though they were found to be less physically active (p < .05). Conclusion: Our study revealed that university students with abnormal BMI values experienced greater cardiac workload, even though they are less physically active. Thus, physical fitness and healthy lifestyle interventions should also include underweight students in addition to students who are overweight or obese.