Effects Of HIT And MCT On Heart Rate Variation In Young Women And Their Training Adaptation

Background:The dynamic balance between sympathetic and parasympathetic nervous system regulates the steady-state control of cardiovascular functions.The dominance of sympathetic control during acute exercise and exercise recovery increases the risk of cardiovascular events,and the risk decreases with exercise training.In addition,high-intensity interval training?HIT?has recently become a popular way of fitness and rehabilitation.However,it is still not clear whether HIT exercise has higher cardiac risk than traditional moderate-intensity continuous exercise.The risk characteristics of different types of HIT training during acute exercise and the adaptation characteristics of different types of training are also unclear.This information will help to assess the cardiac risk of acute exercise in different training programs in training practice.Objective:This study tested the heart rate variability before,during and after five bouts of acute exercises during three typical HIT and one traditional moderate-intensity continuous training in order to understand the regulatory changes of autonomic nerves.Methods:90 young women with no training experience?age:21�2 years old?were randomly divided into four groups:classical high-intensity interval training?HIT?,sprint-interval training?SIT?,repeated-sprint training?RST?,moderate-intensity continuous training?MCT?and no training control group?CON?.HIT is repeated exercise for 4 minutes at 90%V?O_2max exercise intensity with 3min interval;SIT is repeated exercise for 1min at 120%V?O_2max exercise intensity with 1.5min interval;RST is sprint for 6s and rest for 9s with 40 cycles;MCT is continuous exercise at60%V?O_2max exercise intensity.Among them,HIT group,SIT group and MCT group overcome 100kj of mechanical work in the 1st-6th and 13th exercise,200kJ in the 6th-12th and 14th exercise.RST group overcomes 1kg of resistance in the 1st-6th and 13th exercise,1.5kg of resistance in the 6th-12th exercise and 2kg of resistance in the 14th exercise.In the process of four-week training?a total of 14 exercises?.The first exercise test was conducted one week after the end of the first V?O_2max test,the interval between the first exercise and the second exercise was 48 hours,and the 13th exercise was carried out 48 hours after the end of the 12th exercise.The second V?O_2max test and the 14th exercise test were conducted with an interval of 48 hours.The rest of the exercise training subjects are free to arrange in their spare time,and they are guaranteed to train 3 times a week.Select the 1st exercise,the 2nd exercise,the 6th exercise,the 13th exercise and the 14th exercise?updated to high load?to record before exercise?supine position:PRE1;standing position:PRE2?,during exercise?4observation points:the whole exercise process was divided into four parts according to the overcoming mechanical work or the duration of the movement,which is 1ST,2ND,3RD and4TH?and within 30 minutes after exercise?6 observation points:the RR intervals of 256consecutive heartbeats were selected forward to calculate heart rate variability at 5.5min,9.5min,15.5min,19.5min,25.5min and 29.5min respectively,during the recovery period after exercise.Abbreviated as:POST1,POST2,POST3,POST4,POST5 and POST6?.and extract heart rate variability data.It mainly includes root mean square of successive RR interval differences?rMSSD?,standard deviation of normal-to-normal RR intervals?SDNN?,low frequency power?LF?,high frequency power?HF?and the ratio of low frequency power to high frequency power?LF/HF?.Results:In five ECG tests,compared to the supine position before exercise,rMSSD,SDNN and HF decreased significantly while LF and LF/HF increased significantly during acute exercise in the four training programs,and did not return to the pre-exercise level 30min after exercise.Compared with the four training schemes,the highest value of LF/HF was found in RST exercise,while the recovery of rMSSD,SDNN,HF,LF and LF/HF was the fastest after MCT exercise.Compared with the 1st exercise,there was no significant difference in rMSSD,SDNN,HF,LF and LF/HF during and after the second exercise?P>0.05?.The overall results of the6th exercise were similar to those of the 1st and 2nd exercise,except that rMSSD and/or HF increased significantly at the two observation points after the 6th exercise of HIT and SIT?P<0.05?.Compared with the 1st or 2nd exercise,rMSSD increased significantly after the 13th and14th exercise in HIT?P<0.05?,rMSSD increased significantly after 13th exercise in SIT?P<0.05?,and rMSSD decreased significantly after the 14th exercise in RST?P<0.05?.Conclusion:The heart rate variability decreased and the decrease lasted over 30 min after exercise,which reflected the increase of cardiac sympathetic nerve activity and/or the decrease of parasympathetic nerve activity.Compared with the other three training programs,RST exercise showed the highest sympathetic nerve activity,while MCT exercise showed the fastest cardiac autonomic nerve function recovery.After the first or the first to the fifth exercise of the four training programs did not show obvious exercise preconditioning in the improvement of cardiac autonomic nerve functions.Four-week HIT and SIT could improve parasympathetic nerve activation in the recovery period after acute exercise,but four-week RST did not prevent the deterioration of the initial activation of increased motor resistance.