Effects of exhaustive whole-body exercise and caffeine ingestion on muscle contractile properties in healthy men

Background: The influence of exhaustive whole-body exercise and caffeine ingestion on electromechanical delay (EMD) has been underexplored. This study investigated the effect of exhaustive cycling exercise on EMD and other parameters of muscle contractile properties and the potential ability of caffeine to attenuate the exercise-induced impairments in EMD and muscle contractile properties.Methods: Ten healthy men cycled until exhaustion (88 +/- 2% of VO2max) on two separate days after ingesting caffeine (5 mg.kg(-1) of body mass) or cellulose (placebo). Parameters of muscle contractile properties of the quadriceps muscles were assessed via volitional and electrically evoked isometric contractions, performed before and 50 minutes after ingestion of the capsules, and after exercise. Muscle recruitment during volitional contractions was determined via surface electromyography.Results: Exhaustive cycling exercise did not affect volitional and relaxation EMD (P>0.05) but increased evoked EMD. In addition, the exhaustive cycling exercise also increased muscle recruitment at the beginning of volitional isometric muscle contraction (P<0.05). The peak twitch force, maximal rate of twitch force development, and twitch contraction time were all compromised after exhaustive cycling exercise (P<0.05). Acute caffeine ingestion had no effect on muscle contractile properties (P>0.05), except that caffeine increased twitch contraction time at postexercise (P<0.05).Conclusions: Exercise-induced decline in peripheral components of the EMD might be compensated by an increase in the muscle recruitment. In addition, acute caffeine ingestion had minimal influence on exercise-induced changes in muscle contractile proprieties.