Comparison of caffeine and theophylline ingestion: exercise metabolism and endurance

This two-part investigation compared the ergogenic and metabolic effects of theophylline and caffeine. Initially (part A), the ergogenic potential of theophylline on endurance exercise was investigated. Eight men cycled at 80% maximum O(2) consumption to exhaustion 90 min after ingesting either placebo (dextrose), caffeine (6 mg/kg; Caff), or theophylline (4.5 mg/kg Theolair; Theo). There was a significant increase in time to exhaustion in both the Caff (41.2+/-4.8 min) and Theo (37.4+/-5.0 min) trials compared with placebo (32.6+/-3.4 min) (P<0.05). In part B, the effects of Theo on muscle metabolism were investigated and compared with Caff. Seven men cycled for 45 min at 70% maximum O(2) consumption (identical treatment protocol as in part A). Neither methylxanthines (MX) affected muscle glycogen utilization (P>0.05). Only Caff increased plasma epinephrine (P<0.05), but both MX increased blood glycerol levels (P<0.05). Muscle cAMP was increased (P<0.05) by both MX at 15 min and remained elevated at 45 min with Theo. This demonstrates that both MX are ergogenic and that this can be independent of muscle glycogen.