Caffeine increases endurance and attenuates force sensation during submaximal isometric
contractions.
Plaskett, C. J., and E. Cafarelli.
Kinesiology and Health Science, Faculty of Pure and Applied Science, York University,
Toronto, Ontario, Canada M3J 1P3
APStracts 8:0340A, 2001.
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 (Tlim) 1 h after oral caffeine administration (6 mg/kg). Time to reach Tlim 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 Tlim 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 Tlim
may have been caused by a willingness to maintain near-maximal activation longer because of
alterations in muscle sensory processes.
Received 27 October 2000; accepted in final form 25 May 2001
APS Manuscript Number A1006-0.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 29 June 2001