The local hypoxia caused by the strength training (ST) contributes to the increase of muscle activation, which suggests an increase in recruitment of motor units (MU), an important condition to enhance strength and muscle mass. A manner to increase the magnitude of MU recruitment might be the increase of local hypoxia inducted by blood flow restriction (BFR). Thus, the aim of the study is to analyze and compare the effect of local hypoxia during low intensity strength training (LI-ST) with BFR (LIST-BFR: 3-4 x 20/20% of one repetition maximum [1-RM] / 60% of total occlusion pressure), high-intensity strength training (HI-ST: 3-4 x 10/80% of 1-RM) and high intensity strenght training with BFR (HIST-BFR: 3-4 x 10/80% 1-RM / 60% of total occlusion pressure) in muscle activation in young subjects. The hypothesis are that the local hypoxia will be higher for HI-ST and HI-ST-BFR compared to LI-ST-BFR and higher for HI-ST-BFR compared to HI-ST. Moreover, it is expected that the muscle activation will be higher for the HI-ST-BFR and HI-ST compared to LIST-BFR and similar among HI-ST and HI-ST-BFR. In order to test these hypotheses, 18 young men will undergo the three experimental training conditions of strength training randomly, in a crossover design. During the sessions the local muscle oxygenation will be measured by near-infrared espectroscopy (NIRS) and muscle activation by surface electromyography (EMG), both measurements in vastus lateralis (VL). The dependent variables of the study will be the concentration of oxyhemoglobin delta ( [HbO2]), deoxyhemoglobin ( [HHb]), total hemoglobin ( [HBT]) and tissue saturation index ( TSI), RMS (Root Mean Square) normalized by the maximum voluntary contraction (MVC).
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