What primarily determines an individual's VO2 max?

The correct choice is that genetics primarily determines an individual's VO2 max. VO2 max, which represents the maximum amount of oxygen an individual can utilize during intense exercise, is influenced heavily by genetic predisposition. Factors such as muscle fiber composition, cardiovascular efficiency, and lung capacity are largely inherited traits that contribute to this metric.

While training intensity and diet can certainly play significant roles in improving an individual's overall aerobic capacity and endurance levels, the inherent potential for VO2 max is rooted in one's genetic makeup. Furthermore, athletic experience can enhance performance and lead to adaptations over time but does not fundamentally change the biological limits set by one's genetics. Thus, while other factors can modify and improve VO2 max, the baseline capacity is primarily established by genetic factors.