Background: Caffeine is a popular nutritional supplement among athletes. It is frequently used as an ergogenic aid to improve physical performance, delay fatigue, and increase muscle power. However, these effects have not been tested in CrossFit athletes. The aim of this study was to evaluate the effects of acute caffeine supplementation on workout performance, power, markers of muscle damage, and soreness in trained CrossFit men. Methods: Nine men (28 ± 2 years) with experience in CrossFit (2 ± 0.3 years) were investigated in a randomized, double-blind, placebo-controlled crossover trial, with a 7-day washout between treatment periods. The athletes received anhydrous caffeine (CAF: 6 mg / kg body mass) or placebo (PLA) 60 minutes before a CrossFit workout with tasks that involved muscle strength, power, gymnastic movements, and metabolic conditioning. Blood samples were collected for creatine kinase (CK), C-reactive protein, and glucose determination. Workout performance, rating of perceived exertion (RPE), delayed-onset muscle soreness (DOMS), muscle strength (handgrip strength) and power (bench throw, jump squat and countermovement jump) were also evaluated. Results: CAF resulted in higher glucose concentration after workout compared to PLA (+3.2 mmol/L, 95%CI: 2.1 to 4.3 vs +1.5, 95%CI: -0.1 to 3.0 mmol/L, p = 0.01). No differences were found between treatments in workout performance, CK, DOMS, RPE, muscle power and strength. Conclusions: Acute CAF supplementation did not alter performance, markers of muscle damage, power, and RPE in trained CrossFit men.

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