Aerobic power and cardiovascular response to stress

The relationship between aerobic fitness as measured by maximal O2 uptake (VO2max) and the cardiovascular response to laboratory stressors was examined in two experiments. First, 34 male college students were screened on the basis of their heart rate (HR) response to a reaction time-shock avoidance (RT-AV) task. The six individuals showing an average HR increase of 45 beats/min (reactives) and the six subjects showing an average increase of 8 beats/min (nonreactives) did not differ in VO2max (47.7 +/- 2 vs. 48.7 +/- 1 ml.kg-1.min-1, respectively). However, a statistically significant association between a reported family history of hypertension and peak HR response to RT-AV was seen. In the second series of experiments, the plasma catecholamine and cardiovascular responses of eight elite endurance-trained athletes (VO2max 70.6 +/- 1 ml.kg-1.min-1) and eight untrained volunteers (VO2max 45.5 +/- 1 ml.kg-1.min-1) were compared on the following: RT-AV, reaction time for monetary reward (RT-AP), cold pressor, isometric handgrip, and orthostatic challenge (standing). The trained group exhibited a significantly lower mean HR at rest (P less than 0.05), otherwise there were no significant differences between the two groups. The results indicate that although individual differences (e.g., family history of hypertension and high resting HR) can be related to the potential for cardiovascular responses to novel laboratory challenges, the contribution of fitness to this characteristic is much less clear. Further exploration of questions pertaining to fitness and stress should focus on individuals with a predisposition to stress reactivity.