The Correlation Between HRV And Acclimatization And Aerobic Performance Of Athletes At Two Simulated Altitude

Objects:The aim of this study was to investigate the changes of heart rate variability(HRV)at different simulated altitude in different time before and after the incremental-load exercise,and the correlation between HRV and acute mountain sickness(AMS),hypoxic acclimatization,aerobic performance.Methods:12 male middle-distance athletes were tested the V02max by incremental-load exercise on cycle ergometer at the normoxic environment and in the two simulated altitude hypoxic room after 8 hours.Before and after the exercise,Sp02 was tested.The AMS was evaluated after exposure to hypoxia 8 hours,and the indexes of HRV in supine position were tested after 4hous(T4)and 8hours(T8)exposure to the hypoxia and at the normoxic environment and after the incremental-load exercise.Between the two simulated altitude tests there was one-week intermittence.Because of the small number of subjects,nonparametric tests were used:Friedman's test was used to analyze the indexes of HRV at different time for each condition,and the Wilcoxon test to analyze differences between each index of HRV at corresponding time in two conditions or in each condition at two different time.Pearson test or Spearman test were used to determine the degree of association between the variables measured.All analyses were completed using SPSS software.Results?1)The VLF at T4 and TP,VLF,LF,HF,RMSSD at T8 of 2500m are increased compare to ones in normoxia.The VLF,LF and LF/HF both at T4 and T8 of 3500m are increased compare to ones in normoxia,and HF at T8 is decreased.At the 3500m compare to 2500m,the LF/HF increased and pNN50 and RMSSD decreased at T4,HF and pNN50 decreasde at T8.2)Compare to before exercise,the LF/HF increases and other indexes of HRV decrease after exercise both at normoxia and two hypoxic conditions.But there was almost no difference between indexes of HRV in three conditions.3)The LF at normoxia of subjects with AMS is higher than ones without AMS.The LF at normoxia positively correlates with AMS at two hypoxic conditions.4)The LF at normoxia negatively correlates with Sp02 at T8 of 3500m.At T8 of 2500,the TP,LF,HF and RMSSD positively correlate with Sp02.After exercise at 3500m,the HF and RMSSD positively correlate with Sp02,the LF/HF negatively correlates with Sp02.5)The VLF and LF at normoxia have negative correlations with V02max at 3500m.And the TP and VLF of normoxia after exercise have positive correlations with V02max at 3500m.The LF and LF/HF negatively correlate with V02max at T8 of 3500m.The RMSSD of 2500m after exercise negatively correlates with V02max at 2500m.Conclusions:1)At acute hypoxia of 2500m elevation,the regulation of sympathetic and parosympathetic nerves enhances together and maintain the balance of autonomic nerve system with the extension of time.At acute hypoxia of 3500m elevation,the autonomic nerve system lost its balance,but getting better with the extension of time.2)There is no accumulated effect on the changes of HRV from hypoxia and exercise.3)HRV at normoxia could predict the ability of acclimatization at hypoxia above 3000m elevation.HRV at hypoxia below 3000m elevation could predict the ability of acclimatization at the same hypoxic environment.4)Both at nornoxia and hypoxia at rest and after high-intensity exercise HRV could predict the ability of aerobic performance to some extent,but it is different according to the different hypoxic environment.