title: Caffeine ingestion and muscle metabolism during prolonged exercise in humans.
abstract: We examined the effects of a high-caffeine dose on endurance performance and muscle acetyl group metabolism during prolonged exercise. Eight subjects cycled to exhaustion at approximately 80% maximal oxygen uptake (VO2max) 1 h after ingestion of 9 mg/kg body wt dextrose (Pl) or caffeine (Caf). In the Pl trial, muscle biopsies were taken at rest (1 h postingestion) and at 15 min and exhaustion during exercise. The Caf trial followed the same protocol 1 wk later, with an additional biopsy at the time corresponding to Pl exhaustion. The subjects cycled significantly longer during the Caf trial (96.2 +/- 8.8 min) than in the Pl trial (75.8 +/- 4.8 min). Net glycogenolysis during the initial 15 min of cycling was reduced in the Caf vs. Pl trial (4.7 +/- 1.5 vs. 10.6 +/- 1.3 mmol.kg dry muscle-1.min-1; P less than 0.05). Muscle citrate concentration was increased at rest with Caf (0.59 +/- 0.07 vs. 0.37 +/- 0.05 mmol/kg dry muscle; P less than 0.05) but increased to similar values in both trials during cycling. Caf elevated the acetyl-CoA/CoA-SH ratio at rest (0.316 +/- 0.046 vs. 0.201 +/- 0.023; P less than 0.05) but had no effect on the increases in muscle acetyl-CoA and acetylcarnitine during exercise. The results indicate that Caf before exercise decreased muscle glycogenolysis by approximately 55% over the first 15 min of exercise at approximately 80% VO2max. This "spared glycogen" was available late in exercise and coincided with a prolonged time to exhaustion. Increased utilization of intramuscular triacylglycerol and/or extramuscular free fatty acids after caffeine ingestion may inhibit carbohydrate use at rest and early during exercise via elevations in muscle citrate and the acetyl-CoA/CoA-SH ratio. Muscle acetyl-CoA and acetylcarnitine were maintained above resting contents even at exhaustion when muscle glycogen was depleted.
authors.affiliation: School of Human Biology, University of Guelph, Ontario, Canada.
authors.forename: L L
authors.initials: LL
authors.lastname: Spriet
authors.forename: D A
authors.initials: DA
authors.lastname: MacLean
authors.forename: D J
authors.initials: DJ
authors.lastname: Dyck
authors.forename: E
authors.initials: E
authors.lastname: Hultman
authors.forename: G
authors.initials: G
authors.lastname: Cederblad
authors.forename: T E
authors.initials: TE
authors.lastname: Graham
mesh_terms: D000105:Acetyl Coenzyme A / Q000378:metabolism; D000108:Acetylcarnitine / Q000378:metabolism; D000109:Acetylcholine / Q000378:metabolism; D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology*; D002331:Carnitine / Q000378:metabolism; D002951:Citrates / Q000097:blood / Q000378:metabolism; D003065:Coenzyme A / Q000378:metabolism; D004837:Epinephrine / Q000097:blood; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D006801:Humans; D007773:Lactates / Q000097:blood; D008297:Male; D009132:Muscles / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009638:Norepinephrine / Q000097:blood; D010101:Oxygen Consumption / Q000187:drug effects*; D005082:Physical Exertion; D012016:Reference Values
chemical_list: D001786:Blood Glucose; D002951:Citrates; D005230:Fatty Acids, Nonesterified; D007773:Lactates; D002110:Caffeine; D000108:Acetylcarnitine; D000105:Acetyl Coenzyme A; D000109:Acetylcholine; D002331:Carnitine; D003065:Coenzyme A; D009638:Norepinephrine; D004837:Epinephrine