title: Caffeine potentiates low frequency skeletal muscle force in habitual and nonhabitual caffeine consumers.
abstract: The mechanism of action underlying the ergogenic effect of caffeine is still unclear. Caffeine increases the force of muscular contraction during low-frequency stimulation by potentiating calcium release from the sarcoplasmic reticulum. Studies have also suggested an enhancement of lipid oxidation and glycogen sparing as potential mechanisms. Given that several studies have found an ergogenic effect of caffeine with no apparent metabolic effects, it is likely that a direct effect upon muscle is important. Twelve healthy male subjects were classified as habitual (n = 6) or nonhabitual (n = 6) caffeine consumers based on a 4-day diet record analysis, with a mean caffeine consumption of 771 and 14 mg/day for each group, respectively. Subjects were randomly allocated to receive caffeine (6 mg/kg) and placebo (citrate) in a double-blind, cross-over fashion approximately 100 min before a 2-min tetanic stimulation of the common peroneal nerve in a custom-made dynamometer (2 trials each of 20 and 40 Hz). Tetanic torque was measured every 30 s during and at 1, 5, and 15 min after the stimulation protocol. Maximal voluntary contraction strength and peak twitch torque were measured before and after the stimulation protocol. Caffeine potentiated the force of contraction during the final minute of the 20-Hz stimulation (P<0.05) with no effect of habituation. There was no effect of caffeine on 40-Hz stimulation strength nor was there an effect on maximal voluntary contraction or peak twitch torque. These data support the hypothesis that some of the ergogenic effect of caffeine in endurance exercise performance occurs directly at the skeletal muscle level.
authors.affiliation: Department of Neurology and Rehabilitation Medicine and Kinesiology, McMaster University Medical Center, Hamilton, Ontario L8N 3Z5, Canada. tarnopol@mcmaster.ca
authors.forename: M
authors.initials: M
authors.lastname: Tarnopolsky
authors.forename: C
authors.initials: C
authors.lastname: Cupido
mesh_terms: D000328:Adult; D002110:Caffeine / Q000008:administration & dosage*; D000697:Central Nervous System Stimulants / Q000008:administration & dosage*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004558:Electric Stimulation; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D018763:Muscle Fatigue / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology*; D010807:Physical Endurance / Q000187:drug effects / Q000502:physiology; D019966:Substance-Related Disorders / Q000503:physiopathology*; D019415:Torque; D014836:Volition / Q000187:drug effects
chemical_list: D000697:Central Nervous System Stimulants; D002110:Caffeine