Caffeine Ingestion Attenuates Fatigue-induced Loss of Muscle Torque Complexity.

The temporal structure, or complexity, of muscle torque output decreases with neuromuscular fatigue. The role of central fatigue in this process is unclear. Purpose: We tested the hypothesis that caffeine administration would attenuate the fatigue-induced loss of torque complexity. Methods: Eleven healthy participants performed intermittent isometric contractions of the knee extensors to task failure at a target torque of 50% maximal voluntary contraction (MVC), with a 60% duty factor (6 s contraction, 4 s rest), 60 min after ingesting 6 mg[middle dot]kg-1 caffeine or a placebo. Torque and surface EMG signals were sampled continuously. Complexity and fractal scaling of torque were quantified using approximate entropy (ApEn) and the detrended fluctuation analysis (DFA) [alpha] scaling exponent. Global, central and peripheral fatigue were quantified using MVCs with femoral nerve stimulation. Results: Caffeine ingestion increased endurance by 30 +/- 16% (mean +/- SD, P = 0.019). Complexity decreased in both trials (decreased ApEn, increased DFA [alpha]; both P

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