Caffeine is a common ingredient in sports drinks and supplements with manufactures making claims such as ‘improves mental focus’ or ‘aids fat burning’, but what effects does caffeine really have on exercise performance?
Many people report a perceived improvement in exercise performance or enjoyment after caffeine, but any coffee addict will tell you the world is generally a better place after a cup whether exercising or not. Simply put, caffeine makes us feel good, and therefore could make hard exercise more bearable. Caffeine can also heighten alertness and concentration in the short term which could have a beneficial effect in sports or activities where improved mental acuity will impact performance.
In a 2011 study the Carnegie Research Institute, Leeds Metropolitan University found that caffeine ingested 1 hour prior to exercise “maintains a more positive subjective experience during prolonged cycling”. It is possible then that if you feel better during exercise you may work harder. However, according to a study by the Department of Sports Studies, University of Stirling, performance itself was not affected by caffeine during a 100km cycling time trial. The experiment tested eight trained male cyclists over a 100km time trial including pre-determined periods of high intensity exertion. Three separate trials were carried out using 6mg caffeine per kg of body-weight versus a placebo. They concluded that “Caffeine may be without ergogenic benefit during endurance exercise in which the athlete begins exercise with a defined, predetermined goal measured as speed or distance.” Interestingly the study did show that mean heart rates during the high intensity intervals were slightly elevated for the caffeine group without any impact on performance, although no explanation was offered for this effect.
Caffeine reduces blood supply to the heart
Researchers at the University Hospital Zurich and Center for Integrative Human Physiology CIHP inZurich, found that caffeine reduced blood supply to the heart during exercise.
The subjects ingested a 200mg caffeine tablet 50 minutes prior to exercising on a stationary bicycle. They were tested immediately prior and post exercise. One group carried out the exercise in a chamber designed to mimic the effects of high altitude (approximately 15,000ft). Blood flow normally increases in response to exercise, and the results indicated that caffeine reduces the body’s ability to boost blood flow to the muscle of the heart on demand. The ratio of exercise blood flow to resting blood flow, called the myocardial flow reserve, was 22 percent lower in the group at normal air pressure after ingesting caffeine and 39 percent lower in the group in the high-altitude chamber.
Lead researcher Dr. Kaufmann said: “We now have good evidence that, at the level of myocardial blood flow, caffeine is not a useful stimulant. It may be a stimulant at the cerebral level in terms of being more awake and alert, which may subjectively give the feeling of having better physical performance. But I now would not recommend that any athlete drink caffeine before sports. It may not be a physical stimulant, and may even adversely affect physical performance.”
Caffeine levels in drinks and supplements
Exactly how much caffeine is safe to consume is hard to determine as individuals have different tolerances. The Food Standards Agency only gives guidance for pregnant women, saying that 200mg per day should not be exceeded.
A 2011 Glasgow University study tested caffeine content in single cups of coffee in varying sizes from 20 high street coffee shops. They found that caffeine levels varied widely from 50mg to 322mg with three of the shops serving coffee at over 200mg per cup.
A quick look at some popular energy drinks and supplements also shows large variations in caffeine levels:
- Red Bull 80mg per 250ml can
- Monster Energy Drink160mg average (flavours vary) per can
- Grenade Fat Burners 225mg (2 capsule recommended dose, up to 3 times per day!)