Efeito da hipóxia local na magnitude da ativação, força, massa e arquitetura muscular decorrente do treinamento de força
Biazon, Thaís Marina Pires de Campos
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Local hypoxia (i.e. intramuscular) resulting from resistance training (RT) contributes to ions H+ accumulation and decreased muscle pH (i.e. metabolic stress). It has been suggested that the accumulation of these metabolites promotes an increase in the motor units (MU) recruitment and consequent increase in cross-sectional area (CSA) and muscle strength. Nevertheless, it remain sunknown whether the level of local hypoxia can affect the magnitude of these adaptations. Objective: The objective of the study was to analyze and compare the effect of local hypoxia during low-intensity resistance training with blood flow restriction (LI-BFR: 3-4 x 20/20% of one repetition maximum [1-RM] / 60% total pressure of occlusion), high-intensity resistance training (HI-RT: 3-4 x 10/80% of 1RM) and high-intensity resistance training with blood flow restriction (HI-BFR: 3-4 x 10/80% 1-RM / 60% total occlusion pressure) on muscle activation, strength, mass and architecture in young individuals. Methods: Thirty young men were selected and each leg allocated to three experimental conditions through unilateral knee extension in randomized order and counterbalanced after ranking by strength level (1- RM) and vastus lateralis (VL) muscle CSA quartiles. The dynamic maximum force was measured by 1-RM test and CSA acquisition, muscle thickness (MT), pennation angle (PA) and VL fascicle length (FL) was performed through ultrasound images. The training program consisted of 10 weeks with a minimum interval of 72 hours between training sessions and the measurement of muscle activation by surface electromyography (EMG) and deoxyhemoglobin ([HHb]) and oxyhemoglobin ([HbO2]) concentrations through near-infrared espectroscopy (NIRS) of VL, performed during the training session with relative load obtained after the 1-RM, before (T1), after five (T2) and ten weeks (T3) training. Results: The training total volume (TV) was greater for HI-RT and HI-BFR compared to LI-BFR. There was no difference between the groups in regarding the increase of 1-RM, CSA, MT and AP. However, the FL showed higher increase for HI-BFR compared to HI-RT and LI-BFR. Regarding the magnitude of the EMG, the HI-BFR group showed higher values than HI-RT and LI-BFR. On the other hand, [HHb] were higher for HI-BFR and LI-BFR, however there was no difference between groups on the reduction of [HbO2].Conclusion: The level of local hypoxia does not influence the magnitude of the increase of muscle activation, strength, mass and architecture changes after resistance training. However, the addition of local hypoxia seems to have a greater contribution to the adjustments resulting from the low-intensity resistance training compared to high intensity.