Acute Effects Of Exercise Under Blood Flow Restriction On Autonomic Function And Skeletal Muscle Properties In Underweight Young Women

Purpose:This study was aimed to investigate the effects of different levels of blood flow restriction?BFR?combined with resistance exercise on cardiac autonomic function and skeletal muscle properties in underweight young women.The results of our study will help underweight women exercise more scientifically in the future.Methods:20 moderate activity underweight women performed four sets of knee extension in the following five conditions:low load?30%1RM?resistance exercise?LLRT?,low load?30%1RM?resistance exercise combined with 40%(BFR₄₀),60%(BFR₆₀)and 80%(BFR₈₀)BFR and traditional high load?75%1RM?resistance exercise?HLRT?.LLRT,BFR₄₀,BFR₆₀ and BFR₈₀ included 75 repetitions?30+15+15+15?with 30s rest,when 40 repetitions?10+10+10+10?were performed in HLRT with 1min rest.Firstbeat HR monitor was used to record the R-R interval from pre-exercise to 30min post-exercise and analyze heart rate variability?HRV?.Including time domain?heart rate?HR?,the standard deviation of normal intervals?SDNN?,heart rate coefficient variation?SDNN/HR?and root mean square of successive differences?RMSSD??and frequency domain?low frequency?LF ms²?,high frequency?HF ms²?,normalized low frequency?LF nu?,normalized high frequency?HF nu?and LF/HF ratio?.Collecting the sEMG signals of the dominant vastus lateralis,and the subjective feeling during exercise.Blood lactate,microcirculation?blood flow,oxygen saturation?SO₂?,hemoglobin?rHb??and properties of vastus lateralis?maximum radial displacement?Dm?,contraction time and contraction velocity?Vc??were detected at different time points before and after exercise.Results:?1?There were no significant differences in HR,SDNN,SDNN/HR,LF ms² between conditions?P>0.05?.The decrease of HF ms² in three BFR conditions were similar,but they all significantly lower than that of LLRT?P<0.05?.For RMSSD,LF nu,HF nu and LF/HF,there were no differences between LLRT and BFR₄₀?P>0.05?and values in them could recover immediately after exercise.However,the values in BFR₆₀ were significantly different from LLRT?P<0.05?,and could recover within 30min after exercise.What's more,the effects of HLRT and BFR₈₀0 were significantly higher than that of other conditions?P<0.005?,and they could not recover within 30min post exercise.?2?The applied of BFR significantly decreased SO₂ and increased rHb during exercise?P<0.001?,and with the increase of BFR,the range of change increased.For SO₂ and rHb,there were no differences between BFR₄₀0 and BFR₆₀?P>0 05?,as well as BFR₈₀ resulted the greatest changes in SO₂ when compared to the other conditions except BFR₆₀?P?0.003?,and BFR₈₀ also contributed to the substantial growth in rHb when compared to LLRT and BFR₄₀?P<0.05?,so this condition needed more time to recover.For blood flow,BFR₆₀0 increased clearly when LLRT decreased significantly after exercise?P?0.014?.?3?The neuromuscular activation in LLRT and BFR₄₀ were significantly lower than that of HLRT?P?0.007?,when BFR₆₀ and BFR₈₀ could result similar activation when compared to HLRT?P>0.05?.?4?HLRT contributed significantly decreased in Tc post exercise?P<0.05?.For Dm and Vc,LLRT and BFR₄₀ had no effect on them?P>0.05?,and the decline in BFR₆₀ was the least?P<0.05?and could recover within 15min post exercise.Dm and Vc in BFR₈₀ was clearly lower than LLRT and BFR₄₀?P<0.05?,and could recover within 30min post exercise.The decrease in HLRT was the most and significant lower than LLRT,BFR₄₀0 and BFR₆₀?P<0.01?,and this condition could not recover within 30min post exercise.?5?Blood lactate and RPE in LLRT were significantly lower than other conditions?P<0.05?,and RPE in BFR₈₀ was the most obvious when that of BFR₄₀ and BFR₆₀ were similar?P>0.05?.?6?SO₂ was significantly correlated with RMSSD,HF nu and LF nu?P<0.05?,and RPE was significantly correlated with SO₂,LF nu and HF nu?P<0.05?.In addition,Dm and Vc were significantly correlated with SO₂,rHb and RMSSD?P<0.05?.Conclusion:1.LLRT and BFR₄₀ had no significant effect on cardiac autonomic function when BFR₆₀ changes cardiac autonomic function,but it can recover within 30min post exercise.The changes in cardiac autonomic function were similar between BFR₈₀ and HLRT,and they all reduce HRV and take longer time to recover.2.BFR₄₀ does not enhance the training effect when compared to LLRT,and has the disadvantages of reduced SO₂,increased RPE and the accumulation of lactate.BFR₆₀ can produce similar muscle activation and has the characteristics of rapid recovery of skeletal muscle contractility when compared to HLRT.In addition,BFR₆₀ enhances the hyperemia response post exercise.BFR₈₀ does not further enhance the training effect,and RPE in BFR₈₀ is obviously aggravated due to the high levels of BFR.It also results in a significant decline in microcirculation and contractility of working muscle,so it takes longer time to recover.3.Cardiac autonomic function is highly correlated with SO₂ in working muscle,and both of them are related to the contractility of muscle and RPE.4.We recommend BFR₆₀ to underweight women for daily resistance training.