Physical fitness, but not physical activity, is associated with mental health in apparently healthy young adults.

Background: The prevalence of mental health disorders is rising globally. Despite the popularity of exercise as a strategy to improve mental health in individuals with anxiety or depression, there is a paucity of literature on this topic in apparently healthy young individuals who are free from mental illness.

Methods: We characterized relationships between actigraphy-derived physical activity levels and cardiorespiratory fitness (V̇O2max; via maximal graded exercise testing), with mental health assessed using psychometric questionnaires (POMS and PSS) in apparently healthy young adults (26±4.3yrs; 22 women and 26 men).

Results: In women and men combined, relative V̇O2max (33.5±8.1 mL/kg/min) was associated (P<0.01) with POMS (r=-0.454) and PSS (r=-0.510) scores, and relationships between fitness and POMS were preserved (P<0.05) after controlling for body fat (27.2±9.9%). Additionally, V̇O2max was associated (P<0.05) with numerous POMS subcomponents (tension, anger, fatigue, depression, confusion; all P<0.05). No relationships (P>0.05) were observed between physical activity profiles (sedentary time, light intensity time, moderate-vigorous intensity time, total steps, counts per day) with POMS or PSS scores, and only total steps was associated with relative V̇O2max (r=0.331; P=0.021). Relationships between relative V̇O2max and POMS scores were also observed in men (r=-0.407, P=0.039) and women (r=-0.490; P=0.021) individually, but V̇O2max and PSS relationships were exclusive to men (r=-0.516, P=0.007).

Conclusions: Independent of body composition, cardiorespiratory fitness, but not actigraphy-derived physical activity, is associated with mental health in apparently healthy young men and women. To maximize mental health benefits, exercise training interventions are advised to focus on eliciting improvements in cardiorespiratory fitness.