目的：观察昼夜生物节律对自行车运动员运动能力的影响并探讨其生理学机制。方法：15名男子自行车运动员分别于清晨（8：00 a ．m ．）或傍晚（6：00 p ．m ．）在功率自行车上进行1次1 km计时赛测试，实验中，每200 m记录摄氧量（痹VO2）、心率（HR）、平均功率输出（MPO ）、有氧功率输出（APO ）和无氧功率输出（AnPO ）。记录计时赛前、后的口腔温度。于实验前、实验后即刻以及实验后60 min分别取静脉血测定血浆胰高血糖素（PG ）、去甲肾上腺素（NE）、肾上腺素（ADR）、皮质醇（CRT）、生长激素（GH）、胰岛素（Ins）、总睾酮（TTE）、游离睾酮（FTE）、乳酸（LA）和葡萄糖（Glu）含量。结果：与清晨比较，傍晚计时赛成绩提高（即运动时间缩短）（ P＜0．05），MPO、APO和 AnPO增加（ P＜0．05）；将赛程分段分析后发现，傍晚计时赛进行至200 m、400 m、800 m和1000 m时 MPO升高（P＜0．05），至800 m和1000 m时 APO和痹VO2升高（ P＜0．05），至200 m和400 m时 AnPO升高（ P＜0．05）。安静状态下傍晚时口腔体温高于清晨（P＜0．05），但计时赛后的口腔体温并无显著性差异（P＞0．05）。血浆Ins、CRT 、TTE和 FTE在清晨高于傍晚（P＜0．05），GH和 Glu则在清晨低于傍晚（ P＜0．05）；血浆NE和Glu对运动的反应在清晨高于傍晚（ P＜0．05）。结论：自行车运动员的运动能力在傍晚高于清晨（运动成绩提高、功率输出增加），其机制可能与傍晚时体温升高，有氧、无氧代谢供能效率增加，比赛配速调整以及在相关激素作用下形成有利于调动机体生理机能的代谢环境有关。建议运动员按照运动能力的生物节律特征科学、合理的安排日常训练（傍晚训练）以达到最佳训练效果，临近比赛期间通过调整生物节律以保持良好的机能状态与竞技能力。%Objective :To observe the effects of daily biorhythm on exercise capacity in cyclists , investigate the possible physiological mechanism .Methods :Fifteen male cyclists performed a 1000m time trial on cycle ergometer at either 8 :00 a .m .or 6 :00 p .m .and oxygen uptake (VO2 ) ,heart rate(HR) ,mean power output(MPO) ,aerobic power output(APO) and anaero‐bic power output (AnPO ) were recorded every 200m during the trial .Oral temperature was re‐corded pre‐and post‐time trial .Before ,immediately and 60 min post trial ,venous blood samples were collected respectively to determined plasma pancreatic glucagons (PG ) ,norepinephrine (NE) ,adrenalin(ADR) ,cortisol(CRT) ,growth hormone(GH) ,insulin(Ins) ,total testoster‐one(TTE) ,free testosterone(FTE) ,lactic acid(LA) and glucose(Glu) content .Results :Com‐pared with morning ,time trial performance enhanced (ie .the time to complete the time trial re‐duced)(P< 0 .05) ,MPO ,APO and AnPO increased (P< 0 .05) in evening ;by analysis of segmentation of time trial ,MPO at 200m ,400m ,800m and 1000m ,APO and VO2 at 800 m and 1000m ,AnPO at 200m and 400m tended to be higher in evening (P<0 .05) .At rest ,o‐ral temperature was higher in evening than morning (P<0 .05) ,after time trial ,oral tempera‐ture at both two time‐point did not reach significant difference(P>0 .05) .Plasma Ins ,CRT , TTE and FTE were higher in morning than evening (P<0 .05) while GH and Glu were lower in morning than evening ( P< 0 .05 );plasma NE and Glu response to the exercise was in‐creased in morning than evening ( P< 0 .05 ) .Conclusion :Exercise capacity was improved in evening than morning (exercise performance elevated and power output increased ) and the pos‐sible mechanism was related with elevated body temperature ,increased energy efficiency of aer‐obic and anaerobic metabolism ,regulation of pacing during competition ,and the optimal meta‐bolic milieu created under relevant hormonals to transfer physiological functions .Athletes should achieve optimal training effect by scientific and reasonable arrangement of daily training (i .e .training in evening ) according to biological rhythm characteristics of exercise capacity and maintain favorable function state and athletic performance through regulation of biological rhythm close to competition .
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