Aerobic fitness and sympatho-adrenal response to short-term psycho-emotional stress under field conditions.

A possible relationship between aerobic fitness (AF), measured by maximal cycle ergometry (CE) and sympatho-adrenal response to acute, short lasting psycho-emotional stress was investigated by monitoring heart rate (fc) and excretion of catecholamines. The activation of the sympatho-adrenal system was characterised by the noradrenaline: adrenaline ratio. A group of 11 healthy men [22.8 (SD 2.52) years] lived under identical environmental conditions; their mean maximal oxygen uptake (VO2max) was 47.1 (SD 3.9) ml.min-1.kg-1. After the physiological and psychological laboratory tests had been completed the fc of the subjects was monitored continuously during the "guerilla slide" and "parachute jump by night", two emotionally stressful military tasks. Maximal fc (fc, max) attained during these events was 84.5% and 83% of fc, max during CE (fc, max, CE), respectively. A significant relationship (r = -0.92, P < 0.0002) between fc, max reached during the stressful tasks and VO2max was found only for the guerilla slide, which was preceded by physical strain, sleep deprivation and energy deficit. One subject with some prior experience in parachuting showed the lowest fc response and the lowest sympatho-adrenal activation in both events, independent of the degree of AF. In conclusion, AF was found to influence the sympatho-adrenal and fc response to acute, short-lasting emotional stress when the stressful event was aggravated by preceding physical strain, the magnitude of the stress response depending largely on individual experience and effective mechanisms for coping with specific stimuli.