It is estimated that approximately 90 percent of dutch adults drink coffee regularly (Hameleers et al., 2000). Coffee contains caffeine which is known to be a stimulant that affects the central nervous system. The effects of caffeine are mainly caused by an antagonistic action on adenosine receptors. This is due to the increase in levels of many neurotransmitters such as dopamine, acetylcholine and serotonin (fredholm et al., 1999). Many studies have found to that caffeine has a beneficial effect on cognitive performance. It has a positive effect of on performance in terms of vigilance and alertness via acceleration of motor process through central and peripheral mechanisms. Caffeine may therefore play a important part in ones exercise, in order for concentration, time reaction and technical/tactical skills to have a greater effect on both physical and mental performance. .
The usage of caffeine in studies is not very consistent. There are differences in duration of caffeine abstinence, dose, and manner of administration. In some studies, subjects have to abstain from coffee for just one hour before the experiment, while other studies demand abstinence from caffeine for several days. As it has been shown that caffeine has a positive effect in subjects that had only been minimally deprived of caffeine (Christopher et al., 2005; Warburton, 1995; Warburton et al., 2001), we decided to allow subjects to drink their morning cup of coffee. In this way, detrimental effects of caffeine withdrawal symptoms were prevented and the daily ritual of subjects would not be affected (Lane and Phillips-Bute, 1998; Rogers et al., 2003). In previous studies, the doses of caffeine used vary from a single dose of 32 mg (Lieberman et al., 1987) up to 1400 mg of caffeine (Streufert et al., 1997), or bodyweight related doses of 1 (Yeomans et al., 2002) to 13 mg/kg (Pasman et al., 1995). According to Graham (2001), the optimal dose of caffeine is between 3 and 6 mg/kg bodyweight.