Research On Human Body's Heart-muscle Electrophysiological Changes In The 45-day-6° Head-down Bed-rest (HDBR)

Working for long in micro-gravity environment makes astronauts face physical deconditioning which usually represents in the way of changes of motor function.It has become a core research focus of space physiology to understand the mechanisms of physiological changes and to develop countermeasures to alleviate deconditioning progression through the investigation on motor system.However,studies on changes of human physiological system under microgravity or simulated microgravity focus more frequently on lower limbs' antigravity muscle but less on upper limbs.This study mainly focused on the change of upper limbs' EMG under pushing and pulling task and HRV under resting state.Moreover,this study also attempted to make a conjoint analysis between muscle system and cardiovascular system.The simulated microgravity experiment was processed in China Astronaut Research and Training center.Eight healthy males participating in this study performed strict 45-day head-down bed-rest(HDBR).On the 5th day of pre-HDBR,and the 15 th,30th and 45 th days of HDBR,the subjects performed maximum pushing task and maximum pulling task,and sEMG was collected from upper limbs synchronously.Combining one-way ANOVA,this study extracted time-domain,frequency-domain and non-linear features to analyze HRV and sEMG during HDBR.Through the analysis of HRV,we found that as the time of HDBR prolonged,the excitability of sympathetic nervous system increased,but the excitability of vagus nervous system decreased.Each subject's maximum volunteer contractions of both the tasks during these days were compared,showing no significant change.However,changes were detected by sEMG-based analysis.It was found that integrated EMG,root mean square,mean frequency,fuzzy entropy of deltoid,and integrated EMG,root mean square,fuzzy entropy of triceps brachii changed significantly when comparing pre-HDBR with HDBR.The variation trend of these features presented a recovery tendency after significant decline.This finding suggests that electrophysiological parameters are more sensitive to muscle deconditioning than muscle force during prolonged microgravity.Using sEMG's time-domain,frequency-domain and non-linear features,this study processed SVM-RFE pattern recognition and got the accuracy of 73%-98%.This finding shows that selected features have good time sensitivity,also indicates the cross-individual robustness and stability of HDBR.To analyze the correlation effect of cardiac system and muscle system,this study defined conjoint function of HRV features and sEMG features.We found that HDBR influenced on correlation effect of cardiac system and muscle system.These findings could provide technical support for designing countermeasure during space flight and development of space rehabilitation method.