The effect of training on VO2 max, endurance capacity (EC) and ventilation during maximal exercise (VE max) were studied in 17 normal subjects aged 21--51 years. At the beginning of the study 11 of the subjects (eight women and three men) were untrained (U) and six others (three women and three men) trained regulatory (T). A maximal intensity exercise (on a cycle ergometer) which could be sustained for 45 min (MIE45) was performed three times per week for 6 weeks; the total mechanical work (TMW) corresponding to the MIE45 per session varied between 3.14 and 9.24 kJ . kg-1. Before training, VO2 max (a), VEmax (b), and TMW (c) were higher in T than in U subjects. Training increased these variables in most of the subjects; the increase being significantly higher (mean +/- SEM) in U (a = +29.9 +/- 3.8%; b = 49.6 +/- 6.5%; c = 47 +/- 6.9%) than in T subjects (a = 6.6 +/- 3.8%; b = 17.5 +/- 3.6+; c = 19.1 +/- 2.8%). In all but three cases the % increase of TMW was higher than that of VO2 max, suggesting a higher sensitivity of TMW in measuring EC. The significant increase in VE max, maximal voluntary ventilation, peak flows (inspiratory and expiratory) and static maximum voluntary ventilation, peak flows (inspiratory and expiratory) and static maximum pressures indicate that this training protocol improves in healthy subjects the performance of respiratory muscles as well.