Maintaining an active lifestyle is crucial for good health. Markers of health risk include tissue components. This study aimed to indicate which body composition elements create the strongest correlations with physical activity performed in young students of medical faculties. The study group consisted of 75 students (33 men and 42 women) from Wroclaw Medical University. Each student underwent accelerometer and anthropometric measurements and body composition analysis. Both men and women had similar physical activity levels. The study found that the amount of vigorous physical activity correlated significantly with the basal metabolic rate (BMR), fat, water and muscle content, fat-free mass (FFM), bone mass, extracellular to intracellular water ratio (ECW/ICW), and phase angle (PA), with r~ ± (0.2–0.4). The amount of moderate physical activity correlated with body mass, body mass index (BMI), BMR, FFM, and bone mass, with r~0.3–0.5. There are dimorphic differences in the strength of correlations between physical activity and elements of body composition. A greater amount of moderate and vigorous physical activity is associated with greater FFM and bone mass in men, which causes BMI to increase as well (in this case, higher BMI is not a sign of being overweight). For women, the beneficial effect of higher amounts of vigorous physical activity on reducing fat content and increasing muscle mass is more pronounced. In both men and women, an improvement in hydration is evident with increased vigorous physical activity volume.