The present study assessed daily activity, physical capacity and body composition in 11 initially sedentary healthy subjects [5 men and 6 women, mean age 62.8 (SD 2.7) years] before training (T(o)), after completion of 7 (T(7w)) and 14 (T(14w)) weeks of training, and again 6 (T(6m)) and 12 (T(12m)) months after training. The mean daily activity index decreased from T(7w) to T(12m) reaching a lower level than at T(o) [T(12m) - T(o) = -1.5 (SD 4.6) units, P = 0.18]. Mean maximal oxygen uptake (VO(2max)) and its corresponding mean power output (Wdot(max)) were increased by 12.5 (SD 6.6)% (P = 0. 003) and 22.8 (SD 12.8)% (P = 0.003), respectively, at T(14w), and returned to their T(o) levels within 1 year. Mean body mass (m(b)) remained stable until T(6m) but increased significantly by 2.6 (SD 3. 7)% from T(6m) to T(12m) (P < 0.05). Mean fat mass (m(f), from bioelectrical impedance analysis measurements) tended to decrease [-2.0 (SD 4.2)%, P = 0.10] during the training period but increased by 7.8 (SD 10.9)% between T(6m) and T(12m) (P < 0.05). The mean fat free mass did not vary during the study period (P = 0.81) but magnetic resonance imaging (MRI) showed that mean thigh muscle volume decreased between T(7w) and T(12m) to less than at T(o) [T(12m) - T(o) = -2.3 (SD 3.6)%, P = 0.05]. Therefore, this study confirmed the favourable effects of endurance training on the physical capacity and body composition of elderly people, but demonstrated that the training programme would have to be continued to maintain the training-related benefits (i.e. increased VO(2max) and Wdot(max)) which would otherwise be lost within 1 year. After training, m(b) and m(f) were found to be increased. Furthermore, a fast and reproducible MRI protocol was validated for study of small intra-individual variations in tissue volumes in longitudinal studies.