ExPhys -- Discussion, BME @ MTU

A significant increase in maximal oxygen uptake (Fig. 3a) and a significant decrease in mean submaximal heart rate (Fig. 3b) after the training program suggest that exercise training increased stroke volume. However, using non-invasive estimates, we were unable to detect significant changes in stroke volume (Table 1).

Normal hemodynamic effects of endurance training include increased plasma volume, leading to increased stroke volume and cardiac output - which in turn lead to an increased aerobic capacity (VO2max). Other effects of exercise training, such as an increased arterial-venous O2 difference could have contributed to the increased VO2max we report.
B.RRISD increased significantly after exercise (Fig. 4), which indicates increased cardiac parasympathetic control

A high degree of parasympathetic cardiac control is prognostically healthy for the human heart. Our data show that increases in parasympathetic tone can be increased after only 4 weeks of moderate-duration exercise.
Vagal baroreflex gain, assessed during phase IV Valsalva, increased significantly after 4 weeks of moderate aerobic training (Fig. 5).
Exercise ?trains? arterial baroreceptors to function over a wider range of arterial pressures

The ability of the heart rate to decrease more rapidly in response to increases in blood pressure is a cardioprotective adaptation.
Exercise training had no effect on heart rate variability or baroreflex gain during head-up tilt testing.

Cardiovascular regulatory strategies to deal with an orthostatic stress are different in highly trained athletes than in normal, relatively untrained young men, and four weeks moderate-intensity exercise training is not sufficient to induce adaptations that match those seen in athletes.