Date of Award

5-1988

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Medical Sciences

Supervisor

Dr. N. L. Jones

Co-Supervisor

Dr. G. J. F. Heigenhauser

Abstract

Twelve 60-70 and ten 20-30 year old sedentary healthy males participated in this study to determine the effects of endurance training in improving the exercise capacity of elderly individuals and to examine the mechanisms related to oxygen transport that may contribute to any such change. Oxygen intake (VO₂), CO₂ output (VCO₂), ventilation (VE), heart rate, blood pressure, cardiac output, and the ability of muscles to generate short- term power were measured during exercise before and after twelve weeks of high intensity endurance training.

Before training, the elderly had a 37% lower peak V0₂ than the young subjects, associated with a lower peak cardiac output, and arterio-venous oxygen ((a-v)O₂) difference, heart rate and stroke volume and a lower vascular conductance. The capacity to generate short-term power was also about 30% lower in the elderly.

After training, peak VO₂ (1/min) increased from 1.599 ± 0.073 to 2.212 ± 0.073 (38%) in the elderly and 2.536 ± 0.141 to 3.263 ± 0.181 (29%) in the young. Although the extent of the improvement was similar, different mechanisms contributed to the improvement in the two groups.

Firstly, in the elderly, peak cardiac output (1/min) increased from 12.7 ± 0.6 to 16.5 ± 0.4 (30%); the (a-v)O₂ difference (m1/1) increased only by 6% (126.5 ± 3.7 to 134.7 ± 2.7). In the young, there were equal increases in cardiac output and (a-v)O₂ difference (14%). Secondly, the increase in peak cardiac output in the elderly was accompanied by a marked increase in peak stroke volume (78.9 ± 3.5 to 95.6 ± 2.5 ml, 21%), with a smaller but significant increase in peak heart rate (161 ± 3.8 to 173 ± 3.9 beats/min, 7%); in the young, stroke volume and heart rate increased to a similar extent (9% and 5% respectively). In addition, significant increases were observed after training in the elderly in submaximal stroke volume, cardiac output and vascuIar conductance; their systolic blood pressure during submaximal exercise was significantly lower. There were no changes in the young group. The changes in short-term power output were similar in both groups; total work increased by 13% in old and 8% in young, associated with decreases in pIasma Iactate and muscIe fatigue. These changes together with decreases in the RER suggest improved aerobic metabolic processes in muscle.

In conclusion, elderly individuals respond to high intensity endurance training by increases in peak VO₂ that are of the same magnitude as in young subjects. Marked training-associated increases in submaximal and peak stroke volume and cardiac output in the elderly are accompanied by decreases in heart rate, systolic blood pressure and increases in vascular conductance. These changes suggest improvement in the perfusion of exercising muscles which enabled these trained elderly to achieve higher levels of exercise and peak V0₂.

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