咖啡因和耐力的运动员

Caffeine is naturally occurring chemical compound that functions in the body mainly as a mild nervous system stimulant. It has been shown to enhance performance in sprints, in all-out efforts lasting 4-5 minutes, and in longer performance tests.

性能和咖啡因

It appears caffeine enhances performance in shorter events through four interrelated neuromuscular effects:

1. Lowering the threshold for muscle recruitment.
2. 改变激发收缩耦合。
3. Facilitating nerve impulse transmission.
4. 增加肌肉内的离子运输。

In longer events, caffeine delays fatigue by reducing the athlete’s perception of effort. It increases the concentration of hormone-like substances in the brain called ß-endorphins during exercise. The endorphins affect mood state, reduce perception of pain, and create a sense of well-being.

Caffeine has also been found to delay fatigue during exercise by blocking adenosine receptors on fat cells. As a result, caffeine increases the level of free fatty acids in the bloodstream and thereby increases fat burning during exercise. This latter effect of caffeine used to be considered the major mechanism by which is enhanced endurance performance, but it is not known to be a minor factor. In fact, for those who normally maintain a high-carbohydrate diet it is virtually a non-factor.

许多研究表明，摄入咖啡因后，各种耐力学科的表现显着提高。在一项研究中，精英跑步者用咖啡因在跑步机中的时间提高了1.9％。在另一项研究中，咖啡因在循环测试中增加了15分钟的耗尽时间。在一项涉及游泳者的研究中，发现咖啡因可在最多25分钟的最大游泳时提高咖啡因的表现。

Caffeine Is A Diuretic

Caffeine is a diuretic, meaning that it increases urine production, which could theoretically exacerbate dehydration during exercise. However, exercise negates this effect if caffeine. In a recent scientific review, researchers from the University of Connecticut wrote, “Dietitians, exercise physiologists, athletic trainers, and other sports medicine personnel commonly recommend that exercising adults and athletes refrain from caffeine use because it is a diuretic, and it may exacerbate dehydration and hyperthermia. This review, contrary to popular beliefs, proposes that caffeine consumption does not result in the following: (a) water-electrolyte imbalances or hyperthermia and (b) reduced exercise-heat tolerance.”

咖啡因的使用

咖啡因通常在比赛前30到60分钟被耐力运动员使用，以提高竞争性能。咖啡因的细胞生成作用是剂量依赖性的。最大效果以每公斤体重5至6毫克的剂量观察到最大效果。对于150磅的跑步者来说，这大约为340-400毫克，或者您在14至17盎司滴水的咖啡中获得的咖啡因量。平均跑步者必须消耗的最小咖啡因量为可测量的麦克形效应约为每公斤体重2 mg。

It makes less sense to use caffeine as a daily workout performance enhancer, for two reasons. First, workouts are seldom maximal efforts. Second, the ergogenic effects of caffeine consumption decrease with habituation. For this reason, if you are a regular coffee drinker, you should cease coffee consumption four to six days before participating in a race.

In moderation, caffeine consumption does not cause any health problems. In fact, a daily cup of joe is good for you. The health benefits of coffee come from its caffeine content and its unique blend of antioxidants. According to Harvard Medical School, “Studies show that the risk for type 2 diabetes is lower among regular coffee drinkers than among those who don’t drink it. Also, coffee may reduce the risk of developing gallstones, discourage the development of colon cancer, improve cognitive function, reduce the risk of liver damage in people at high risk for liver disease, and reduce the risk of Parkinson’s disease.”

However, heavy caffeine use can cause or exacerbate problems ranging from headache to insomnia, and it is possible to become physically dependent on the drug. Caffeine is especially harmful when used as a means to stimulate artificial wakefulness or energy in those suffering from conditions such as chronic fatigue. So if you do like caffeine, limit yourself to one mug of coffee or green tea in the morning. Those who rely on regular “caffeine injections” throughout the day are well advised to cut back.

Caffeine and Sports Drinks

An alternative to taking a single large dose of caffeine prior to racing is to consume a caffeinated sports drink throughout races. In a recent study, conducted at the University of Birmingham in England, looked at the effect of caffeine on exogenous carbohydrate oxidation (i.e. the rate at which carbs consumed in a supplement are burned) during exercise. Cyclists received either a 6% glucose solution, a 6% glucose solution plus caffeine, or plain water during a two-hour indoor cycling test. Researchers used indirect calorimetry to measure the amounts and proportions of fat and carbohydrate oxidized during the test.

他们发现，接受咖啡因碳水化合物的骑自行车的人的外源碳水化合物氧化速率比没有咖啡因的碳水化合物高26％。该研究的作者得出的结论是，咖啡因可能会增加肠中葡萄糖吸收率，从而更快地为工作肌肉提供燃料。对性能的可能影响可能是能够在更长的时间内更加努力而不会疲劳。

最近的另一项研究研究了在温暖的环境中食用含咖啡因的运动饮料对性能的影响。16名受过训练的骑自行车的人完成了三项试验。受试者循环135分钟，在头120分钟内每15分钟每15分钟交替在60％至75％的VO2max之间，然后进行15分钟的性能。在一次试验中，他们消耗了风味的水；在另一种情况下，一种常规的碳水化合物运动饮料；在另一种情况下，一种含咖啡因的运动饮料。

在咖啡因试验期间，骑自行车的人比其他两项试验完成了15％至23％的工作。与安慰剂和传统的运动饮料相比，用含咖啡因的运动饮料的感知劳累的评分低于含咖啡因的运动饮料。骑自行车后，发现含咖啡因的饮料的最大强度损失比其他饮料要少三分之二。