Acute Neuromuscular And Physiological Changes Before And After Repeated Sprint Training Under Normoxic And Hypoxic Conditions

Background:In recent years,more and more studies have found that compared with repeated sprint training in Normoxia（RSN）,repeated sprint training in Hypoxia（RSH）can effectively improve maximum repeated sprint ability of athlete,interval exercise efficiency,and performance of sport.Studies have shown that hypoxia may promote the recruitment of fast-twitch fibers,thereby improving athletic performance,but the effect of RSH on the degree of muscle activation is still unclear.Therefore,the purpose of this study is to compare the differences in physiological stress,fatigue and repeated sprint performance after acute RSH and RSN,as well as the effects of RSH and RSN on the activation of skeletal muscle,which provides new ideas for improving the performance of specific athletes,and provides reference for scientific researchers and coaches in the practical application of hypoxic training.Methods:13 amateur male athletes participated in the study.Subjects are physically active on an endurance exercises（at least 3 times a week）,The test performs repeated sprint training for 10×6 seconds under different oxygen concentrations（RSH:Fi O₂=13%,RSN:Fi O₂=21%）and 24 second passive recovery under normoxic and hypoxic.Measuring the subject’s blood oxygen saturation,blood lactate concentration,and the cross-sectional area of the lateral femoral and rectus femoris before the test.Collect the repeated sprint performance indicators,heart rate,and surface EMG signals of the lateral femoris and rectus femoris muscles during the test.RPE and blood oxygen saturation were recorded immediately after the test,and the blood lactate was measured at the 5,7 and 9 minutes after the test.There should be at least 48 hours between tests under the two oxygen concentrations to ensure that the test content and sequence are exactly the same.The study performs paired-samples T test to compare the differences in cross-sectional area of muscle between the two groups.Performing two-way analyses of variance for repeated measures（ANOVA）to compare the blood lactate concentration and blood oxygen saturation before and after the test（group×time）under two oxygen concentrations and performing linear regression and paired-samples T test to determine whether there are differences in the performance indicators of repeated sprints under different oxygen concentrations and surface EMG indicators.Result:（1）Compared with RSN,arterial oxygen saturation after RSH decreaseds significantly（p<0.05）,but arterial oxygen saturation and heart rate changes slightly decrease but not significantly different（p>0.05）.（2）The cross-sectional area of the rectus femoris and lateral femoris muscles of the two groups are significantly increase after repeated sprint protocol（p<0.001）,and the increase after RSH was significantly greater than that of RSN（p<0.05）.（3）After simple linear regression and paired-samples T test,it is find that the mean frequency of EMG of the rectus femoris under hypoxic is significantly lower than that in RSN（p<0.05）.（4）Compare with the normoxic,the peak velocity,mean velocity,and percentage decrement score also decrease significantly in RSH（p<0.05）.Conclusion:The blood oxygen saturation of human body in hypoxic condition is significantly lower than that in normoxic,which makes the mean power frequency of lower limb muscle surface EMG in repeated sprint training in hypoxic significantly lower than that in repeated sprint training in normoxic,and the muscle swelling of lower limb is significantly higher than that in repeated sprint training in normoxic.The increase of fatigue will eventually lead to the decline of performance in repeated sprint training in hypoxic,which is significantly higher than that in repeated sprint training in normoxic.