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; Gaff), or theophylline (4.5 mg/kg Theolair; Thee). There was a significant increase in time to exhaustion in both the Caff (41.2 +/- 4.8 min) and Thee (37.4 +/- 5.0 min) trials compared with placebo (32.6 +/- 3.4 min) (P < 0.05). In part B, the effects of Thee on muscle metabolism were investigated and compared with Gaff. 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 Thee. This demonstrates that both MX are ergogenic and that this can be independent of muscle glycogen.