Efeitos agudos do exercício físico realizado com diferentes níveis de restrição do fluxo sanguíneo sobre a reatividade vascular de jovens

Abstract

Low intensity resistance training performed with blood flow restriction (BFR) promotes favorable muscle adaptations in young and older people. However, its effects on vascular function are still little known. Objective: To elucidate the acute effects promoted by physical exercise with BFR on vascular function. Methods: The thesis is structured in five chapters, as follows: a) chapter 1 - Introduction b) chapter 2– systematic review, with specific searches in pubmed, web of science, scopus and cochrane library, to understand the state of the art with the questions: "What are the acute effects promoted by BFR on endothelial function in exercise or without exercise?" and "What are the effects of different levels of BFR on the endothelial function?"; The available evidence suggests that increased exercise-related shear stress leads to greater release of NO and increased FMD. The addition of BFR seems to mitigate this response. A dose-response relationship between retrograde blood flow caused by BFR and reduced endothelial function seems to occur in healthy and recreationally active young individuals, but not in older individuals. c) chapter 3 - design of the original protocol; d) chapter 4 – The original study in which 12 young males were evaluated, aged 18 to 25 years, eutrophic and sedentary, randomized to perform three experimental protocols: i) blood flow restriction (ExBFR) – handgrip exercise with intensity of 30% of the maximum voluntary contraction (MVC) combined with low level of BFR performed through an inflated pressure cuff at the value of 80% of occlusive blood pressure (OBP) at rest; ii) occlusive blood pressure (ExOBP) – handgrip exercise with intensity of 30% of MVC combined with vascular occlusion performed through an inflated pressure cuff at the value of 120% of resting PAO; iii) control (ExCON) – handgrip exercise with intensity of 30% of the MVC performed under a free flow condition, that is, the pressure cuff placed in the proximal third of the upper limb but is not inflated. In all conditions, the exercise was performed at the rate of 30 contractions/min until voluntary fatigue. All volunteers were evaluated for vascular reactivity by venous occlusion plethysmography (dependent and independent endothelium vasodilation). Forearm blood flow (FBF), after reactive hyperemia, increased significantly in the three experimental models immediately after exercise, when compared to their baseline before-exercise conditions (p<0.05). When compared to their before-exercise hyperemia conditions, the ExBFR and ExCON protocols did not show significant differences immediately after exercise (p>0.05), but there was a decrease in the FSA value in reactive hyperemia in the ExOBP condition immediately after exercise when compared to pre-exercise reactive hyperemia situation (-23.7%; p<0.05). The FBF after reactive hyperemia did not show significant variation in the three experimental models 30 minutes after exercise, when compared to their pre-exercise reactive hyperemia conditions (p<0.05). The percentage increment of hyperemia/basal presented reductions in all experiments in the situation immediately after the exercise, when compared to the pre-exercise (ExBFR = -71.61%; ExCON = -64.6% and ExOBP = - 77.5% p<0.05). e) chapter 5 – Final considerations. Conclusion: Through the results obtained in the original study of the thesis, it was concluded that a single session of handgrip exercise caused an acute increase in the FBF immediately after the exercise in the different protocols, tending to a reduction of the FBF in the reactive hyperemia immediately after the exercise in the ExOBP group, but returning to baseline values 30 min after the end of the exercise.