Caffeine Supplementation and Muscle Endurance - a Balanced Placebo Design Study

Abstract

1,3,7-trimethylxanthine is one of the most consumed psychoactive substances in the world, found in a wide variety of foods and drinks. About 74% of athletes during international and national competitions use caffeine (CAFF) aiming to improve performance. Its effect on aerobic exercise is well known; however, on strength training, more information is needed to determine it. A key point that might help explain such controversies is the placebo effect and its interactions with CAFF use. PURPOSE: We aim to analyze the effect of acute caffeine supplementation on muscle endurance using a balanced placebo design to study the physiological effect of CAFF (5 mg/kg of body weight) and the placebo effect. METHODS: Five young men underwent six sessions, one for familiarization, one as control and four experimental ones. At the first session, they were submitted to anthropometric measurements, CAFF consumption questionnaire and one repetition maximum test (1RM) in the parallel squat (Smith’s machine). At the second session they performed 3 sets to exhaustion with 3 minutes interval between sets using 60%1RM - it’s the muscle endurance test (MENT). The last four sessions were randomly distributed using a balanced placebo design having four possibilities: 1 - Session C/C: Subject was informed of CAFF ingestion and was given CAFF. 2 - Session C/P: Subject informed of CAFF ingestion but given placebo (PLA) 3 - Session P/C: Subject informed of PLA ingestion but given CAFF. 4 - Session P/P: Subject informed of PLA ingestion and given PLA. Subjects received CAFF or PLA on arrival at the laboratory then waited about 1h20min to execute the MENT. RESULTS: No CAFF effects were observed on the maximal number of repetitions done (p>0.05) - 32.6, 35.0, 33.8 and 32.0, neither on the number of repetitions done at first set (p>0.05) - 16.2, 15.6, 15.8, 15.0 - or on the last set (p>0.05) - 7.4, 8.2, 8.0, 7.2 - during sessions C/C, C/P, P/C, P/P, respectively. Three of the five subjects appeared as CAFF responders (increased 2.2 repetitions average) and two exhibited a PLA effect (increased 3.0 reps average). CONCLUSION: CAFF has no effect on the MENT. Some people may be responsive to CAFF while others may actually present a PLA effect. The use of balanced placebo design seems to be an important method for clarifying future studies results using CAFF supplementation.