Introduction: Previous studies have shown links of body composition and fitness measures with brain structure, as well as with different aspects of emotional adjustment and well-being. However, the possible role of trait emotion-regulation success in the relationship between fitness/body composition and emotion-related subcortical structures has never been directly addressed.
Methods: Twenty-three elite helicopter pilots were assessed in fat mass percentage, an endurance test to volitional exhaustion, bench-press power output, and negative urgency (trait affect regulation failure). Their brains were scanned using magnetic resonance imaging to estimate the size of the accumbens/amygdala, considered together, and the thalamus. Resulting correlations were used to test the relationship between body composition/fitness measures and brain structures' size, and the role of negative urgency therein, using structural equation modeling.
Results: Fat mass percentage was associated with the size of the thalamus and the amygdala/accumbens. In the latter case, negative urgency and bench-press power output predicted structure size (and explained the effect of fat mass percentage away). In other words, bench-press power output and emotion regulation success (but not endurance performance) were associated with a larger amygdala/accumbens size.
Conclusions: Bench-press power output and emotion regulation success are independently associated with a larger amygdala/accumbens size, although present evidence does not allow for determination of causal directionality.