EVIDENCE OF VASCULAR FUNCTION PLASTICITY INDUCED BY SMALL MUSCLE TRAINING

According to the American Heart Association and the World Health Organization, cardiovascular disease is the primary cause of death. Interestingly, the female incidence of mortality due to cardiovascular events has clearly exceeded that of male since 1984. Physical exercise is the most important non-pharmacological treatment leading to several cardiovascular protective effects via a direct impact on the vasculature and on the autonomic response. In the modern society, not everyone could practice physical activity on a daily basis, because of several limitations or more simply, particular diseases in which the traditional physical exercise approach results unfeasible. Exercise-related improvements in vascular functionality are primarily attributed as shear stress- dependent mechanism.Respiratory muscles being part of the musculoskeletal system can be trained. Because of this, it is possible that respiratory muscle training (RMT) could be used as an alternative exercise paradigm causing alteration in the peripheral hemodynamic, including no exercising areas, to improve vascular health. Previous evidences proved that RMT has a primary positive effect in static and dynamic lung volumes, together with maximal inspiratory pressure, and a secondary important effect in increase cardiac vagal tone, lastly affecting the autonomic nervous system balance. To date, the effects of RMT on the overall vasomotor response (a well-recognized marker of cardiovascular health) has not been investigated yet. Another small muscle exercise modality is the dynamic knee extension. The ability of the vessels to alter their diameter (i.e. vasodilation or vasoconstriction) to maintain the homeostasis of the vascular tone, ensuring that the blood flow matches the demand of the skeletal muscles and other organs, both at rest and during exercise is defined vasomotor response. Extrinsic factor, such as the autonomic control of the sympathetic neural drive (global control), and intrinsic factor such as the capacity of the endothelial cells to respond to mechanical stress by releasing vasoactive molecules (i.e. nitric oxide, NO) together with other possible factors, such as pH and temperature, interact to determines the prevalence of a vasoconstriction or vasodilator effect on the arterial wall. Thus, the aim of this dissertation was to evaluate the effects of two different types of small muscle exercise training on the peripheral vasomotor response in young healthy people. Two studies were developed in which the purposes were: 1) to evaluate the effects of eight weeks of RMT on both central (i.e. the balance between the sympathetic and parasympathetic neural system assessed by heart rate variability) and peripheral (i.e. the ability of the endothelium to release NO causing vasodilatation assessed by Flow Mediated Dilatation(FMD) components of vasomotor response, in young healthy females; 2) to evaluate the effects of single-leg knee extension training (KE) on vasomotor response in the lower limb directly involved with exercise (i.e. femoral artery) and on the upper limb, not involved with KE (i.e. brachial artery). We hypothesized that (i) RMT could improve FMD in the brachial artery (beneficial effect on peripheral control due to systemic factors influenced by exercise training) via a reduction in sympathetic drive (central control), and that (ii) KE could raise the peripheral blood flow also in limb non-directly involved in the exercise leading to positive effects in both exercised and not exercised limbs. The positive effects observed in the present dissertation, in terms of increase in vascular function parameters, after KE training and RMT, may suggest that also small muscle exercises are able to raise peripheral BF in both involved and non-involved exercising area. However, positive adaptation in the peripheral component of the vasomotor response could be detected after training only when the peripheral blood flow stimulus was strong enough to trigger a series of positive adaptation on the vessels.