Caffeine increases isometric muscle strength regardless of expectation: a balanced placebo design study

Introduction: Caffeine (CAFF) is the most widely consumed psychoactive substance in the world. A recent meta-analysis showed that the effect of caffeine supplementation in maximum strength (MS) is modest. Thus, is caffeine’s effect actually a placebo effect? Purpose: The aim of this study was to evaluate the effect of caffeine supplementation on MS differentiating its physiological effect of the expectation effect (placebo effect). Methods: Young men (n=16) participated in six sessions: Familiarization, control and four experimental sessions. First a familiarization with a dynamometer (System IV, Biodex Medical) was performed and personal and anthropometric data were collected. In the second session (control), the isometric MS test was performed after a standardized warm-up; this was repeated in all experimental sessions. All four of them were performed using the balanced placebo design. Session C/C: Subject was informed that he would receive CAFF and was given CAFF; Session C/P: Subject was informed that he would receive CAFF but was given placebo (PLA); Session P/C: Subject was informed that he would receive PLA but was given CAFF; Session P/P: Subject was informed that he would receive PLA and was given PLA. Subjects waited 1h to perform the isometric MS test after receiving CAFF (5 mg/kg of body weight) or PLA. A 2x2 ANOVA (informed x received) was performed. An alpha level of 5% was adopted. Results: Figure 1 presents Peak Isometric Torque in each experimental session. Use of CAFF significantly increased strength (p<0.05) compared to placebo – 326.5±49,4 N.m vs 313.2±49,1 N.m. Post-hoc analysis (Bonferroni) showed differences in absolute peak torque in C/C (given caffeine/received caffeine) and P/P (informed placebo/received placebo) sessions (327.0±55.4 N.m vs 310.0±54.4 N.m). There was no interaction between caffeine usage and the information received. Conclusion: CAFF supplementation increases MS, and this is not affected by the information given. The expectation of receiving CAFF by itself did not increase MS. CAFF supplementation may be especially beneficial for competitive athletes, where small differences separate the first from the last - further research on this subject is needed.

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