It is exceedingly apparent that caffeine is not effective for non-trained individuals participating in high-intensity exercise. This may be due to the high variability in performance that is typical for untrained subjects. Results, however, are strikingly different for highly-trained athletes consuming moderate doses of caffeine. Collomp et al. [46] examined the use of 250 mg of caffeine (4.3 mg/kg) in trained and untrained swimmers. Swimmers participated in two maximal 100 m freestyle swims; significant increases in swim velocity were only recorded for the trained swimmers. Similar results were reported by MacIntosh and Wright [74] in a study

that examined the effects of caffeine in trained swimmers, but the caffeine treatment was provided at a higher dose (6 mg/kg) and the protocol involved a 1,500-meter MDV3100 swim. Results indicated a significant improvement in swim times for those subjects who consumed caffeine, as compared to placebo. Moreover, time was measured at 500-m splits, which resulted in significantly faster times for each of the three splits for the caffeine condition [74]. As suggested

by Collomp et al., [29] it is possible that specific physiologic adaptations present in highly trained ZD1839 anaerobic athletes, such as enhanced regulation of acid-base balance (i.e., intracellular buffering of H+), is intrinsic for caffeine to exert an ergogenic effect [29]. Participants in a study published by Woolf et al. [30] were highly trained anaerobic athletes, and results of that investigation demonstrated a significant increase PR-171 solubility dmso in peak power with a moderate dose

of caffeine (5 mg/kg) as compared to placebo [30]. Wiles et al. [44] reported a 3.1% improvement in performance time for a 1-kilometer time trial (71.1s for caffeine; 73.4s for placebo) at a caffeine dose of 5 mg/kg, and results also included a significant increase in both mean and peak power [44]. Wiles et al. [44] indicated that subjects in the study reported regular interval sprint training, which may support the theory that caffeine is most beneficial in trained athletes who possess physiological adaptations to specific high-intensity training P-type ATPase [44]. A recent study published by Glaister et al. [31] examined a 5 mg/kg dose of caffeine on sprint interval performance. Subjects were defined as physically active trained men and performed 12 × 30 m sprints at 35 s intervals. Results indicated a significant improvement in sprint time for the first three sprints, with a consequential increase in fatigue for the caffeine condition [31]. The authors suggested that the increase in fatigue was due to the enhanced ergogenic response of the caffeine in the beginning stages of the protocol and, therefore, was not meant to be interpreted as a potential negative response to the supplement [31]. Bruce et al. [32] tested two doses of caffeine (6 mg/kg, 9 mg/kg) on 2000 m rowing performance in competitively trained oarsmen.