Background: In the 21st century, with the rapid development of many human life areas, physical activity should be prevalent in health maintenance and promotion. Body posture is a motor habit characteristic of every individual. Its correctness depends on numerous aspects, e.g., physical activity, age, mental state, or eating habits. There are numerous reports in the literature on the impact of physical activity on body posture, correct foot arch development, and the level of aerobic capacity in children and adolescents, but there is a noticeable lack of assessments of these characteristics and their correlations in adults. Aim: To evaluate aerobic capacity in males and females in relation to selected body posture elements. Methods: The study involved 45 females and 46 males aged 20–21 years. The inclusion criteria involved declared good health and no contraindications. Selected somatic traits, body posture, and physical capacity indicators were determined. Results: Physical capacity shows a significant relationship with body mass in both sexes (female: r = −0.346; p = 0.020; male: r = −0.321; p = 0.030). A significant correlation was observed between aerobic capacity and lean body mass in females (r = −0.428; p = 0.003) and body mass (r = −0.461; p = 0.001) and body fat percentage in males (r = −0.443; p = 0.002). A significant correlation was demonstrated between maximal oxygen uptake and Clarke’s angle (r = −0.300; p = 0.045) in females, between maximal oxygen uptake and the loaded area of the right foot (r = −0.247; p = 0.098) in the male group, and between maximal oxygen uptake and spine lateral deviation (r = 0.352; p = 0.018) in females. There was no dimorphism between body posture elements and physical capacity except for the level of foot longitudinal arches, feet loading surface, spine lateral deviation, and the range of spine mobility in the sagittal and frontal planes. Aerobic capacity significantly influenced lean body mass (β = −0.379; p = 0.007) and spine deviation from the anatomical axis in the frontal plane in females (β = 0.287; p = 0.039) and body fat percentage in males (β = −0.443; p = 0.002). Conclusions: Selected body posture elements demonstrate relationships with physical capacity in both sexes. The results should find wide practical applications, e.g., in promoting a comprehensive assessment of body posture and physical capacity as determinants of health maintenance.