The aims of the present study were to define the respective roles of the cardiac and respiratory response to exercise as determinants of the age-related physiological decrease in exercise performance, and to assess the relationship between aging and interindividual variability in the response to effort. We studied 91 normal subjects recruited in three age-groups: Group A (42 children, aged 10+/-2 years); Group B (29 young adults, aged 27+/-5 years); Group C (20 elderly,aged 74+/-9 years). All the subjects underwent an incremental cycle ergometer exercise test with ct work load increase of 15 W every 2 minutes in groups A and C, and 25 W every 2 minutes in group B, until they achieved 80% of the predicted maximal heart rate. Ventilatory equivalent changes during exercise were significantly lower in group A than in the other two groups, and in group B compared to group C. Exercise-induced changes in oxygen pulse were significantly higher in group A, but no difference was found between groups B and C. Thus, gas-exchange function and overall exercise performance decrease with advancing age, whereas cardiovascular performance is well maintained in normal elderly subjects. Discriminant analysis showed that the exercise response conformed to the group-specific model in 74% and 79% of subjects in groups A and B, but only in 50% of the group C subjects; 5% and 45% of the elderly subjects were functionally classified in groups A and B, respectively. On the basis of these data, it may be concluded that aging accounts for a dramatic increase in interindividual variability in adaptation to physical effort, and that the inverse relationship between age and exercise performance is mainly related to the declining efficacy of the respiratory response to effort with age.
