Effect of Cardiorespiratory Fitness on Cortisol and Cardiorespiratory Responses to Concurrent Mental and Physical Stress

Abstract

Aerobic fitness is associated with increased sensitivity to mental challenge, evidenced by a relative elevation in heart rate (HR) response, and enhanced efficiency, demonstrated by a relative attenuation in absolute HR. However, the impact of aerobic fitness on cardiorespiratory and hypothalamic pituitary adrenal (HPA) activation in responses to mental challenge during exercise has not been investigated. PURPOSE: This study compared cortisol (CORT) and cardiorespiratory responses between individuals with below average fitness (VO2max = 34.29 ± 0.99 ml/kg/min-1) and individuals with above average fitness (VO2max = 48.04 ± 1.60 ml/kg/min-1). METHODS: Forty-eight apparently healthy individuals (24 high fit [HF] and 24 low fit [LF]) participated in two counter-balanced experimental conditions. In one condition, the participant was mentally challenged while exercising on a cycle ergometer at 60% of VO2max (dual-stress condition; DSC) and the other in which the participant exercised at the same intensity without the mental challenge (exercise-alone condition; EAC). State anxiety measures and the NASA Task Load Index (NTLX) were used to assess perceived mental and physical workload during each condition. RESULTS: State anxiety and NTLX scores were elevated in the DSC. The DSC also elicited greater elevations in HR, respiration rate, ventilation, ventilatory efficiency and CORT values. Additionally, HF individuals demonstrated significantly lower CORT levels (HF = 11.59 ± 0.83 nmol/L; LF = 15.17 ± 0.55 nmol/L; p = .01) in the DSC following the conclusion of the mental challenge. CONCLUSIONS: These results suggest that a mental challenge during a physical challenge impacts the cardiorespiratory system and activates the HPA axis, and that increased fitness levels may attenuate these effects.