It is well documented that caffeine ingestion increases the endurance of young people exercising at 60%-85% of their maximal oxygen uptake (13;15;47). It also seems to improve endurance as measured by repeated sub-maximal isometric contraction (42), and decreases the rate of perceived exertion during exercise (6;9;46). Typically, doses of approximately 6 mg/kg caffeine were used in these studies.