Effects of caffeine ingestion on exercise performance at low and high altitudes in cross-country skiers.

The effect of caffeine on exercise time over a specified distance (approx. 21 km) was investigated in well-trained cross-country skiers (14 subjects) both at low (300 m above sea level) and high (2900 m above sea level) altitudes. Each subject participated in two races at both altitudes--one after caffeine ingestion (6 mg/kg body weight) and one after placebo on a double-blind basis. In each race 50% of the participants were medicated with caffeine, thereby after normalization (where the mean time was set at 100%), when the influence of weather and snow conditions were minimized, the difference between the race time with caffeine and placebo could be calculated for each individual and expressed as a percentage of the mean. At low altitudes, after half the distance, the race time with caffeine was decreased 0.94% of the mean time (corresponding to approx. 33 s) as compared to placebo (P less than 0.05), whereas after the full distance the corresponding decrease was 1.7% of the mean time (corresponding to approx. 59 s) (0.05 less than P less than 0.10). At high altitudes, the race time was significantly faster with caffeine than with placebo (P less than 0.001), both after one and two laps, 2.19% and 3.18% of the mean time, respectively (corresponding to approx. 101 s and 152 s). The perceived exertion was similar at low and high altitudes independent of medication. In conclusion, there are indications that caffeine induces an increased performance capacity for cross-country skiers at low altitudes. Furthermore, an even more marked improvement after caffeine as compared to placebo was found at high altitudes.