title: Caffeine increases endurance and attenuates force sensation during submaximal isometric contractions.
abstract: Caffeine has known ergogenic effects, some of which have been observed during submaximal isometric contractions. We used 15 subjects in a randomized, double-blind, repeated-measures experiment to determine caffeine's ergogenic effects on neuromuscular variables that would contribute to increased endurance capacity. Subjects performed repeated submaximal (50% maximal voluntary contraction) isometric contractions of the right quadriceps to the limit of endurance (T(lim)) 1 h after oral caffeine administration (6 mg/kg). Time to reach T(lim) increased by 17 +/- 5.25% (P < 0.02) after caffeine administration compared with the placebo trial. The changes in contractile properties, motor unit activation, and M-wave amplitude that occurred as the quadriceps reached T(lim) could not account for the prolonged performance after caffeine ingestion. In a separate experiment with the same subjects, we used a constant-sensation technique to determine whether caffeine influenced force sensation during 100 s of an isometric contraction of the quadriceps. The results of this experiment showed that caffeine reduced force sensation during the first 10-20 s of the contraction. The rapidity of this effect suggests that caffeine exerts its effects neurally. Based on these data, the caffeine-induced increase in T(lim) may have been caused by a willingness to maintain near-maximal activation longer because of alterations in muscle sensory processes.
authors.affiliation: Kinesiology and Health Science, Faculty of Pure and Applied Science, York University, Toronto, Ontario, Canada M3J 1P3.
authors.forename: C J
authors.initials: CJ
authors.lastname: Plaskett
authors.forename: E
authors.initials: E
authors.lastname: Cafarelli
mesh_terms: D000328:Adult; D002110:Caffeine / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D004558:Electric Stimulation; D004576:Electromyography; D004594:Electrophysiology; D006439:Hemodynamics / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000187:drug effects*; D008297:Male; D018763:Muscle Fatigue / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects*; D010807:Physical Endurance / Q000187:drug effects*
chemical_list: D000697:Central Nervous System Stimulants; D002110:Caffeine