The pressor response to involuntary isometric exercise of young and elderly human muscle with reference to muscle contractile characteristics.

Changes in heart rate (fc) and blood pressure (BP) were observed in eight healthy young men aged [mean (SD)] 20 (1) years and ten healthy elderly men aged 65 (5) years, during electrically evoked contractions of the ankle plantar flexors and elbow flexors which were sustained for 2 min. There was no significant difference in the fc response to evoked contraction of the ankle plantar flexors or elbow flexors between young and elderly subjects. During contraction of the elbow flexors, elderly subjects produced an unexpectedly large rise in systolic BP which was significantly greater than that of the young subjects. The exaggerated response seen in the elderly group may be due to a more rigid arterial tree which is thought to occur with advancing age. Electrically evoked contraction of the slower contracting elderly ankle plantar flexors resulted in a significantly diminished diastolic BP response when compared with that of the young subjects. In contrast, during electrically evoked contraction of the elbow flexors, which showed a similar twitch time course in young and elderly subjects, the diastolic BP response was not significantly different between groups. This may reflect differences in the peripheral reflex input to the pressor response in elderly arm and leg muscles which, in turn, may be influenced by relative fast twitch fibre area.