Pethick J, et al. - This study was performed to test the speculation that caffeine administration would attenuate the fatigue-induced loss of torque complexity. The current study showed that the caffeine ingestion slowed the fatigue-induced loss of torque complexity and increased the time to task failure during intermittent isometric contractions, in all the probability through central mechanisms.

Methods

• Total 11 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), 1 hour after ingesting 6 mg[middle dot]kg-1 caffeine or a placebo.
• In this study, torque and surface EMG signals were sampled continuously.
• Complexity and fractal scaling of torque were evaluated utilizing approximate entropy (ApEn) and the detrended fluctuation analysis (DFA) [alpha] scaling exponent.
• Global, central and peripheral fatigue were measured utilizing MVCs with femoral nerve stimulation.

Results

• They noticed caffeine ingestion increased endurance by 30 +/- 16% (mean +/- SD, P = 0.019).
• Complexity reduced in both trials (decreased ApEn, increased DFA [alpha]; both P < 0.01), as global, central and peripheral fatigue developed (all P < 0.01).
• Complexity reduced significantly more slowly following caffeine ingestion (ApEn, -0.04 +/- 0.02 vs. -0.06 +/- 0.01, P = 0.004; DFA [alpha], 0.03 +/- 0.02 vs. 0.04 +/- 0.03, P = 0.024), as did the rates of global (-18.2 +/- 14.1 vs. -23.0 +/- 17.4 N.m.min-1, P = 0.004) and central (-3.5 +/- 3.4 vs. -5.7 +/- 3.9 %[middle dot]min-1, P = 0.02) but not peripheral (-6.1 +/- 4.1 vs. -7.9 +/- 6.3 N.m.min-1, P = 0.06) fatigue.