People who want to do sports, but find exertion unpleasant, can probably benefit from a high dose of caffeine. Psychologists at Leeds Metropolitan University discovered that caffeine makes physical exertion more pleasurable.
The researchers were interested to find out more about the mental effects of caffeine. As we know, caffeine is a stimulant. Endurance athletes run five kilometres faster if they've had a dose of caffeine, [J Sci Med Sport. 2008 Apr;11(2):231-3.] and caffeine also helps strength athletes to get more reps out of their sets. [Int J Sport Nutr Exerc Metab. 2007 Oct;17(5):468-77.] But how come this is the case? Does caffeine banish fatigue? Or does caffeine improve your mood, and thus enhance your performance?
To find out the Brits got 12 endurance athletes to cycle for ninety minutes at 70 percent of their VO2max. On one occasion the subjects took a placebo an hour before the experiment started, and on the other occasion they took 6 mg caffeine per kg bodyweight. By the way, this is a dose that can cause side effects in some people.
In an American study performed in 2010, at this dose some of the female subjects "exhibited intense emotional responses, including an expressed inability to verbally communicate, focus, and/or remain still, as well as the feeling of wanting to cry." You have been warned.
During the cycling and the first hour afterward the researchers asked the subjects how they felt at regular intervals. When they asked the athletes how tired they were, the researchers received a predictable response: caffeine reduced feelings of exhaustion.
This effect is shown in the figure below.
The researchers also asked the subjects to what extent they were experiencing feelings of pleasure. This is when they discovered that caffeine prevented the athletes from feeling less happy about the experience while they were cycling. So caffeine makes exertion more pleasurable, or at least less unpleasant. This effect is shown in the figure above.
"The findings have demonstrated that this supplementation regime was associated with a maintenance effect in relation to feelings of pleasure and lowered perceptions of effort", the researchers write. "The observation of positive subjective effects may partially explain the ergogenic effects of caffeine".
Appetite. 2011 Aug;57(1):247-52.