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Left ventricular adaptations following short-term endurance training

¹Faculty of Physical Education and Health, and ²Toronto Hospital Network (General Division) and Heart and Stroke/Richard Lewar Centre of Excellence, University of Toronto, Toronto; and ³Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada

Submitted 9 March 2004 ; accepted in final form 17 September 2004

This study examined the effects of short-term endurance training (ET) on the left ventricular (LV) adaptation and functional response to a series of exercise challenges with increasing intensity. Eight untrained men, with a mean age of 19.4 ± 0.5 (SE) yr, were studied before and after 6 days of ET consisting of cycling 2 h/day at 65% peak aerobic power (O_2max). LV ejection fraction and LV volumes were assessed by radionuclide angiography at rest and during exercise at three uninterrupted successive work rates corresponding to 53, 68, and 83% of O_2max, each lasting 20 min. ET produced a calculated plasma volume expansion of 11.4 ± 2.2% (P < 0.05). The increase in plasma volume was accompanied by an increase in O_2max from 45.9 ± 1.9 to 49.0 ± 1.0 ml·kg^–1·min^–1 (P < 0.01) and a decrease in maximal heart rate (197 ± 2.3 to 188 ± 1.0 beats/min; P < 0.01). Resting LV function was not changed, although there was a trend for higher stroke volumes (SVs) and improvement in the rapid filling phase of diastole (P = 0.08). Training induced an increase in exercise SV by 10.4, 10.2, and 7% at 53, 68, and 83% O_2max, respectively (P < 0.01). These changes were secondary to increases in end-diastolic volume, which increased significantly at each exercise work rate following training (139 ± 6 to 154 ± 6 ml at 53% O_2max, and from 136 ± 5 to 156 ± 5 ml at 83% O_2max; P < 0.01). End-systolic volumes were unchanged after ET. A significant bradycardia was observed both at rest (decreasing 7%) and exercise (decreasing 10.4%). LV ejection fraction during exercise was increased slightly by training, reaching significance at the highest work rate, after 60 min of exercise. (P < 0.05). Cardiac output was higher following training at the highest workload (20.8 ± 2.2 vs. 22.9 ± 3.1 l/min; P < 0.01). These data indicate that short-term training elicits rapid adaptation to the LV functional response exercise, with increases in SV being secondary to a Frank-Starling effect with minor changes in contractile performance. This produced a volume-induced bradycardia and increase in LV filling, which may be of benefit during prolonged exercise.

left ventricle; exercise; endurance training; radionuclide imaging

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