The exercise prescription: focus on vascular mechanisms.
Recent recommendations by expert bodies for reducing cardiovascular risk factors have included accumulation of 30 min/day of moderate activity in an intermittent fashion. There is little support for this recommendation for blood pressure reduction, the most effective, proven exercise regimens being of moderate intensity, performed three or four times per week for durations of not less than 30 min. Although cycling and jogging have proven efficacious in blood pressure reduction, walking provides less benefit but might be preferable for older individuals, and for those with orthopedic and cardiac limitations. There are preliminary indications that moderate swimming programs reduce the systolic blood pressure. Benefit in reducing other risk factors including the lipid profile, insulin sensitivity, body composition and weight, neurohumoral factors and cardiac structure and functioning has also been shown to occur with continuous bouts of exercise. Vascular adaptation represents a particular mechanism of benefit. Aerobic training increases the large-artery compliance, contributing to a reduction in systolic blood pressure and an attenuation of the cardiac afterload. The release of endothelially derived nitric oxide increases with regular exercise and might modulate changes in arterial compliance to some extent. Moderate cycling for 4 weeks increased basal nitric oxide production in previously sedentary normal and hypercholesterolemic individuals. Highly trained athletes had increased forearm endothelium-dependent vasodilator reserve. This effect, if it is translatable to the coronary circulation, might provide protection against ischemia. The efficacy with which an increase in physical activity can impact on cardiovascular risk factors will depend largely on adherence to exercise programs. Adherence could improve with lower intensity, intermittent programs. Further study in this area is warranted in order to determine the impact of such interventions on risk factors and vascular changes.
Kingwell
BA
Alfred and Baker Medical Unit, Baker Medical Research Institute, Prahran, Australia.
Jennings
GL