Soares, E. M., Molina, G. E., & Fontana, K. E. (2016). Caffeine supplementation and muscle endurance – a balanced placebo design study. Medicine & Science in Sports & Exercise, 48(5), Supplement abstract number 257.

This study analyzed the effect of caffeine supplementation on muscle endurance using a balanced placebo-design to study the physiological effects of caffeine (5 mg/kg of body weight) and a placebo. Young men (N = 5) underwent six sessions, one for familiarization, one as a control, and four experimental conditions. At the first session, Ss were measured anthropometricly, a caffeine consumption questionnaire was completed, and a one-repetition maximum test (1-RM) in the parallel squat (Smith’s machine) was completed. At the second session, Ss performed three sets to exhaustion with a three-minute interval between sets using 60%1-RM as the muscle-endurance test. The last four sessions were randomly distributed using a balanced placebo-design having four possibilities: i) Session C/C: S was informed about caffeine ingestion and given caffeine; ii) Session C/P: S was informed about caffeine ingestion but given a placebo; iii) Session P/C: S was informed about placebo ingestion but given caffeine; and iv) Session P/P: S was informed about placebo ingestion and given the placebo. Ss received caffeine or the placebo upon arrival at the laboratory then waited approximately one hour and 20 minutes to execute the muscle-endurance test.

No caffeine effects were observed for the maximum number of repetitions completed or on the number of repetitions completed on the first set or last set during the four experimental conditions. Three of the five subjects appeared to be caffeine-responders (increasing 2.2 repetitions on average) and two exhibited a placebo-effect (increasing 3.0 repetitions on average).

Implication. Caffeine had no effect on a muscle-endurance test. Some Ss were responsive to caffeine while others exhibited a placebo-effect. The use of a balanced placebo-design seems to be an important method for clarifying the effects of supplements on performance.

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