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Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada N1G 2W1
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 O2 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 O2 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.
adenosine antagonism; ergogenic; methylxanthines; adenosine 3',5'-cyclic monophosphate; catecholamines
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