Effects Of Exercise Under Different Levels Of Blood-flow Restriction On Autonomic Modulation And Muscular Fatigue

PURPOSE: To assess the acute cardiac autonomic and peripheral muscular responses to eccentric exercise combined with different levels of blood flow restriction (BFR) in young women. METHODS: Twenty-five women (21.22±0.61 year) performed 4 sets of leg extension (30 + 15 + 15 + 15 repetitions) at 20 % one repetition maximum, with four different BFR conditions (0, 40, 60, and 80 %). Restrictive pressures were calculated based on blood-flow measurements taken at rest on each subject. Heart rate variability (HRV) and muscle fatigue were recorded at rest and during 24 hour of recovery by calculating time (RMSSD) and frequency domain (LF nu, HF nu, LF/HF) indices and analyzing muscle displacement (Dm) and contraction velocity (Vc) values, respectively. RESULTS: All parameters in CON (0%BFR) did not significant change (P>0.05). In BFR40, there was a slight reduction in RMSSD (18.51%) and HF nu (12.19%) compared to CON (P<0.05). In BFR60, RMSSD and HF nu decreased 27.91% and 13.98% while LF nu increased 13.77% compared to CON (P<0.05), and LF/HF recovered within 30min post exercise (P>0.05). In BFR80, LF nu increased 16.43% while RMSSD, HF nu, Dm and Vc dramatically declined 39.92%, 15.41%, 37.34% and 48.85% respectively when compared to CON (P<0.01), so it took longer time to restore LF/HF balance (within 24 hours). Correlation analysis showed that RMSSD was positively correlated with Dm (r = 0.65) and Vc (r = 0.62), respectively (P<0.05). while LF nu was negatively correlated with Dm (r =﹣0.57)and Vc (r =﹣0.59) (P<0.05). CONCLUSION: On the basis of low load resistance exercise, 40% BFR can withdraw vagal regulation, but sympathetic activity and sympathetic/ parasympathetic balance can be enhanced when the restriction increased to 60%BFR. Peripheral muscular fatigue can just be obviously evoked in 80% BFR, and this fatigue is highly related to cardiac autonomic modulation. Therefore, we do not recommend 80% BFR for women with cardiovascular risk.