The Effect Of Caffeine On The Performance Of Endurance Athletes Under Incremental Exercise And Stead State Exercise In Hypoxic Condition

Objectives:The aerobic capacity is the key to the performance of endurance athletes.Hypoxic training has been widely used as one of the effective ways to improve aerobic capacity.The intensity and volume of training during hypoxic training are important factors affecting the training effect.Due to the individual differences in the reduction of peak oxygen consumption(VO_2peak)under hypoxic condition,some high-level endurance athletes with a large degree of decline cannot maintain the set training intensity and volume,resulting in neuromuscular decline and no improvement in performance.Studies have shown that the degree of decrease in VO_2peak is negatively correlated with the degree of increase in peak minute ventilation(VE_peak).Therefore,if there is any way to increase VO_2peak by increasing VE_peak under hypoxic conditions,it may be possible to maintain the intensity and volume of training.Objective 1 of this study:To investigate the effect of moderate doses of caffeine（6 mg/kg）on the gaseous metabolism of endurance athletes during incremental exercise under hypoxic condition equivalent to simulated altitude of 2500 m,in order to verify the effect of caffeine on improving training intensity in hypoxic condition and to ensure the effectiveness of hypoxic training.Objective 2 of this study:To investigate the effect of moderate doses of caffeine（6 mg/kg）on metabolism and time to exhaustion of endurance athletes during stead state exercise under hypoxic condition equivalent to simulated altitude of2500 m,and to evaluate the improvement effect of caffeine on training volume.Methods:This study contains 2 research.Method of research 1:In a double-blind,crossover,randomized placebo-controlled trial,16 male endurance athletes ingested caffeine capsules（6 mg/kg,caffeine group）and empty capsules（placebo group）.One hour after capsule ingestion,5-min resting measurements were collected by Cortex.Afterwards,the athletes entered the hypoxic condition with a simulated altitude of 2500 m and began exercising at a work load of 60 Watt while the load was increased by an additional 30 Watt every minute until the subject could not maintain the desired pedal frequency.During this period,gaseous metabolism indexes and heart rate（HR）were recorded in real time,and the subjective feeling of exertion（Rating of Perceived exertion,RPE）and dyspnea were asked and recorded every two minutes.Fingertip blood was taken to measure blood lactic acid（BLA）at 1,3,and 5 minutes after exhaustion.Indicators include:Minute ventilation（VE）,Tidal volume（VT）,Breath frequency（BF）,Oxygen consumption（VO₂）,Carbon dioxide production（VCO₂）,Respiratory exchange rate（RER）,Partial pressure of end-tidal carbon dioxide（PetCO₂）,Partial pressure of end-tidal oxygen（PetO₂）,HR,arterial oxygen saturation（SpO₂）,BLA,incremental exercise time,Peak power output（PPO）,All statistical calculations were conducted with SPSS28.0 software.All data were presented as mean and standard deviation（SD）.Method of research 2:In a double-blind,crossover,randomized placebo-controlled trial,16 male endurance athletes ingested caffeine capsules（6 mg/kg,caffeine group）and empty capsules（placebo group）.One hour after capsule ingestion,5-min resting measurements were collected by Cortex.Afterwards,the athletes entered a hypoxic condition with a simulated altitude of 2500 m and cycled at 80%of the PPO until exhaustion.During the period,gaseous metabolism indexes and HR were recorded in real time.RPE and dyspnea were asked every two minutes.Fingertip blood was taken to measure BLA at 1,3,and 5 minutes after exhaustion.The indicators are the same as in research 1.All statistical calculations were conducted with SPSS 28.0 software.All data were presented as mean and SD.Results:Research 1:（1）In terms of ventilation indicators,there was no interaction between ingested substances and time（P>0.05）,and VE,VT,and BF increased significantly as exercise progressed.VE_peak and BF_peak of the caffeine group were significantly higher than those of the placebo group at the time of exhaustion（P<0.05）,but there was no significant difference in VT_peak（P>0.05）.（2）In terms of metabolic indicators,there was no interaction between ingested substances and time（P>0.05）,and VO₂ and PetO₂ increased significantly as exercise progressed.VO_2peak and PetO₂ of the caffeine group were significantly higher than those of the placebo group at the time of exhaustion（P<0.05）,but there was no significant difference in SpO₂（P>0.05）.（3）In terms of exercise performance,the incremental exercise time and PPO of the caffeine group were significantly higher than those of the placebo group（P<0.05）.（4）In terms of HR,there was no interaction between intake of substances and time（P>0.05）,and HR increased significantly as exercise progressed.There was no significant difference in HR_peak between the caffeine group and the placebo group at the time of exhaustion（P>0.05）（5）In terms of RPE and dyspnea,there was no significant difference in RPE and dyspnea between the caffeine group and the placebo group（P>0.05）Research 2:（1）In terms of exercise performance,the TTE of the caffeine group was significantly higher than that of the placebo group（P<0.05）.（2）In terms of ventilation indicators,the VE of the caffeine group was significantly higher than that of the placebo group at the time of exhaustion（P<0.05）,but there was no significant difference between VT and BF（P>0.05）.（3）In terms of BLA,the BLA of the caffeine group was significantly higher than that of the placebo group（P<0.05）.（4）In terms of HR,the HR of the caffeine group was significantly higher than that of the placebo group（P<0.05）.（5）In terms of RPE and dyspnea,the RPE of the caffeine group was significantly higher than that of the placebo group（P<0.05）,but there was no significant difference in dyspnea（P>0.05）.Conclusion:This study found that ingestion of 6 mg/kg caffeine can significantly improve ventilation capacity in hypoxic condition and improve aerobic endurance performance in hypoxic condition.Research 1 proves that caffeine intake can improve aerobic capacity in hypoxic condition,and can increase VO_2peak by increasing VE_peak.In addition,research 2 demonstrated that caffeine intake can increase VE under stead state exercise and prolonged exercise time.