Figure 3. The relationship between VO₂peak, mitochondrial parameters, and physical activity.

Regression analyses were used to evaluate relationships between physical activity (total and moderate-to-vigorous), cardiorespiratory fitness (VO₂peak) and muscle oxidative capacity (JO₂). Whole-body VO₂peak was positively associated with total step counts (A) and MVPA (B). Modest but significant positive associations were evident between skeletal muscle oxidative capacity (JO₂) and step counts (C) and MVPA (D). A modest but significant positive association was evident for VO₂peak and JO₂ regardless of whether VO2 peak is normalized to total body weight (E) or lean mass (F). Blue symbols are males and red symbols are females. YM: young male; YF: young female; OM: old male; OF: old female. BW: body weight; JO₂: maximal ADP-stimulated oxygen consumption; MVPA: moderate to vigorous physical activity.