Effect of time of day on post-small muscle-mass exercise vasodilation

Abstract

Aerobic exercise training is recommended for reducing systolic and diastolic blood pressure. A single session of aerobic exercise decreases blood pressure during the recovery period, this phenomenon is called post-exercise hypotension. This response has been attributed to a decrease of systemic vascular resistance due to a sustained post-exercise vasodilation. Many factors may affect post-exercise hypotensive mechanisms, and in a previous study, we reported that blood pressure decrease after evening but not morning exercise was accompanied by a decrease in systemic vascular resistance, suggesting that exercise at this time of day may induce greater local vasodilation; which need to be tested. Recently, Dr. Halliwill´s group developed a small muscle-mass dynamic exercise model that allows for investigation local vasodilation. Thus, by employing this model of exercise, it would be possible to test the aforementioned hypothesis. Thus, the objective of this study is to compare local sustained vasodilation following a single-leg dynamic exercise performed in the morning and the evening. For this, 12 healthy adults will undergo two experimental sessions in a randomized order: one performed in the morning (7:30-11a.m.) and another in the evening (5-8:30p.m.). In each session, the subjects will perform a single-leg knee-extension exercise with the dominant leg (60% of peak power - 45 Kicks/min for 60 min) and the rested leg will be used as a control. Before and every 15 min for 180 min after the exercise, heart rate (electrocardiogram), systolic and diastolic blood pressures (oscillometric automatic device), leg blood flow (doppler ultrasound) will be assessed. A three way ANOVA for repeated measures will be employed for data analyses. Data will be expressed as mean ± standard deviation. Pd0.05 will be set as significant. (AU)