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The effects of prolonged strenuous exercise on beta-receptor responsiveness in male and female triathletes Scott, Jessica


The purpose of this investigation was to determine whether alterations in p-receptor responsiveness occur as a result of a single bout of prolonged strenuous exercise (PSE), and whether the myocardium of males and females responds differently to PSE. We examined nine male and eight female triathletes during three separate sessions: before, immediately after, and 24h following a half-ironman triathlon. Athletes were assessed during each session using dobutamine stress echocardiography. Steady-state graded infusions of dobutamine were used to assess p-adrenoreceptor responsiveness. Slopes calculated from linear regressions between dobutamine doses and changes in heart rate and contractility for each subject were used as an index of (3-adrenoreceptor responsiveness. Fractional shortening decreased from baseline after the race in both males and females, with the decrease greater in males (males: 54.1 ±2.1 to 50.7 ± 3.4% vs. females: 55.4 ± 2.7 to 53.3 ± 2.5 %). Despite no change in preload, systolic function (stress-shortening relationship) was significantly decreased in males and females following PSE. The amount of dobutamine necessary to increase HR 25 beats min⁻¹ (males: 29.6 ± 6.6 to 42.7 ± 12.9 μgkg⁻¹min⁻¹ vs. females: 23.5 ± 4.0 to 30.0 ± 7.8 ugkg⁻¹min⁻¹) and contractility 10 mmHg-cm- 2 (males: 20.9 ± 5.1 to 37.0 ±11.5 μg kg⁻¹min⁻¹ vs. females: 22.6 ± 6.4 to 30.7 ± 7.2 μg kg⁻¹ min⁻¹) was significantly greater in both males and females post-race, with the amount of drug necessary to induce this change significantly greater in males. These results provide evidence that an acute bout of PSE results in reduced LV systolic function and dobutamine responsiveness in both males and females and that these alterations occur to a greater extent in males.

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