Cardiorespiratory kinetics during exercises of different muscle groups and mass in old and young

The purpose was to compare cardiorespiratory kinetics during exercises of different muscle groups (double-leg cycling us. treadmill walking and single-leg ankle plantar flexion) in old and young subjects. Oxygen uptake (Vet) during exercise transitions was measured breath by breath, and the phase 2 portion of the response was fit by a monoexponential for determination of the time constant (tau) of VO2. Two separate studies were performed: in study 1, 12 old (aged 66.7 yr) and 16 young (aged 26.3 yr) subjects were compared during cycling and ankle plantar flexion exercise, and in study 2, five old (aged 69.6 yr) and live young (aged 24.4 gr) subjects were compared during cycling and treadmill walking, VO2 transients during square-wave cycling exorcise acre significantly slower in the old compared with the young groups. In contrast, VO2 kinetics did not differ between old and young groups during plantar Aexion exercise. Heart rate (HR) kinetics followed the same pattern, with tau(HR) being significantly slower in the old vs. young groups during transitions to cycling but not to plantar flexion. In study 2, tau(VO2) and tau(HR) during on-transients to treadmill square-wave exercise were significantly slower in the old group compared with the young group, but tau(VO2) was significantly faster during treadmill exercise than during cycling in the old group. The differences with aging between the modes of exercise may be related to the muscle mass involved and the circulatory demands. On the other hand, slowed VO2 kinetics with age appear to occur in a mode (cycling) in which the muscles are not accustomed to the activity, whereas in a mode of normal activity (walking) and with the muscle groups (plantar flexors) accustomed to the activity, VO2 kinetics are not slowed to the same degree with age.