Effects Of Low-temperature Environment Exercise On Mucosal Immune Function And Stress Level In The Saliva Of Cross-country Skiers

Research Purpose:Scientific sports training monitoring can help achieve breakthroughs in competitive sports performance.Among them,physiological and biochemical monitoring is a major component of training monitoring.Cross-country skiing,as the foundation of the Winter Olympic Games,is the focus of the world’s winter sports powers competing for medals.The athletes of this event train and compete for a long time in low temperature environment,which leads to the decrease of mucosal immune function and the enhancement of stress response,which affects the training and competitive state.Saliva,as a non-invasive detection method,plays an increasingly important role in sports training monitoring.To explore the change characteristics of the indicators of mucosal immune function and stress level in saliva of cross-country skiers during exercise in low temperature environment can provide theoretical basis and practical guidance for training evaluation and function monitoring of cross-country skiers.Research Methods:In a randomized crossover experiment design,fifteen male professional cross-country skiers（19.93±1.65 years old,181.93±5.38cm,68.6±5.74kg,average training years of 3.80±0.83 years）were selected as the research subjects.In the environment of 23±1.1℃at normal temperature and-5±0.8℃at low temperature,and relative humidity of about 60%,the power bike was cycled for 1h at the intensity of about50%maximal oxygen consumption(VO_2max)and 75%VO_2max.A total of 4 experiments were performed(50%VO_2max at normal temperature,75%VO_2max at normal temperature,50%VO_2max at low temperature,75%VO_2max at low temperature),each experiment was separated by at least 7 days.Saliva samples were collected before exercise,immediately after exercise,1h after exercise,and 24h after exercise.The indicators reflecting mucosal immune function（Secretory Immunoglobulin A（Secretory Immunoglobulin A,s Ig A）,alpha-amylase,lysozyme,and lactoferrin）and stress level（testosterone and cortisol）were detected in the samples.The data were analyzed by repeated measurement of variance in 2（ambient temperature:normal temperature and low temperature）×2(exercise intensity:50%VO_2maxand 75%VO_2max)×4（time:before exercise,immediately after exercise,1h after exercise and24h after exercise）,and Bonferroni correction was used for post-event analysis.P<0.05indicates a significant difference and P<0.01 indicates a very significant difference.Research results:（1）Indicators of mucosal immunity:（1）The interaction between time×temperature×intensity of s Ig A concentration and secretion rate was significant（F=14.456,P=0.000;F=3.526,P=0.019）.At either temperature,the intensity of 75%VO_2max immediately after exercise and 1 h after exercise were very significantly lower than before exercise（all P<0.01）.At either temperature,exercise at 75%VO_2max intensity immediately after exercise was significantly lower than after exercise at 50%VO_2max intensity（all P<0.01）.Exercise at75%VO_2max intensity immediately after exercise and 1h after exercise in low temperature environment were very significantly lower than exercise at 75%VO_2max intensity at normal temperature（P<0.01）.（2）The time×intensity interaction betweenα-amylase concentration and secretion rate was significant（F=10.087,P=0.000;F=54.000,P=0.000）.The concentration immediately after exercise at 50%VO_2max intensity was significantly higher than that before exercise（P<0.05）.The immediate concentration and secretion rate after exercise at 75%VO_2max intensity were significantly lower than before exercise（P<0.01）,and the secretion rate at 1h after exercise was still significantly lower than before exercise（P<0.05）.The concentration and secretion rates immediately and 1h after exercise at 75%VO_2max intensity were significantly lower than those after exercise at 50%VO_2max intensity（P<0.05）.（3）The time×intensity interaction between lysozyme concentration and secretion rate was significant（F=25.636,P=0.000;F=21.643,P=0.000）.Immediately after exercise and 1 h after exercise at 50%VO_2max intensity were significantly higher than before exercise（P<0.05）,immediately after exercise at 75%VO_2max intensity were significantly lower than before exercise（P<0.01）,and the secretion rate 1h after exercise was still significantly lower than that before exercise（P<0.05）.Immediately after exercise and 1h after exercise at 75%VO_2maxintensity were significantly lower than those at 50%VO_2max intensity（P<0.01）.（4）The interaction of time×temperature×intensity between lactoferrin concentration and secretion rate was significant（F=4.661,P=0.005;F=2.632,P=0.041）.At any temperature,immediately after exercise at 75%VO_2max intensity was significantly lower than before exercise（P<0.01）,and 1h after exercise at low temperature was still significantly lower than before exercise（P<0.01）.Immediately after exercising at 75%VO_2max intensity at low temperature was significantly lower than that after exercising at 50%VO_2max intensity and at normal temperature（all P<0.01）.（2）Indicators of stress level:（1）The time×intensity interaction of testosterone concentration was significant（F=10.320,P=0.000）.The concentration of testosterone immediately after exercise at 75%VO_2max intensity was significantly higher than that before exercise and after exercise at 50%VO_2max intensity（P<0.01）.（2）The interaction of time×temperature×intensity of cortisol concentration was significant（F=3.893,P=0.010）.At any temperature,the cortisol concentration immediately after and 1h after exercise at 75%VO_2max intensity was significantly higher than that before exercise（P<0.05）and after exercise at 50%VO_2max intensity（P<0.01）.In a low temperature environment,immediately after exercise at any intensity and 1h after exercise,it was very significantly higher than that in normal temperature environment（P<0.01）.（3）The time main effect of testosterone/cortisol was very significant（F=12.986,P=0.000）,and the level immediately after exercise and 1h after exercise was significantly lower than that before exercise（P<0.05）.The temperature main effect was very significant（F=12.055,P=0.001）,and it was significantly lower at low temperature than at room temperature（P<0.01）.Research conclusions:（1）Cross-country skiers who perform long-term high-intensity exercise at any temperature will reduce the level of mucosal immunity level;The degree of mucosal immunosuppression was greater after high-intensity exercise at low temperature.（2）Cross-country skiers who perform long-term high-intensity exercise at any temperature will increase the level of physical stress;After high-intensity exercise in a low temperature environment,the body’s stress response is greater.