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No acute effects of placebo or open-label placebo treatments on strength, voluntary activation, and neuromuscular fatigue

Abstract

Purpose

Recent evidence suggests that deception may not be necessary for placebos to improve clinical outcomes. We tested the hypothesis that placebo and open-label placebo (OLP) treatments would acutely improve strength and voluntary activation, as well as minimize neuromuscular fatigue, in untrained participants.

Methods

Twenty-one males (n = 11) and females (n = 10) visited the laboratory on three occasions (placebo, OLP, control) to receive each treatment in a randomized, counter-balanced manner. Trials involved a pretest, a 15-min intervention, and posttests. For the placebo trial, participants were informed that they would be ingesting a capsule that would improve their performance and make them feel more energetic. For the OLP intervention, participants were told that the capsules would have no effects. In “Experiment #1”, knee extensor maximal voluntary contraction (MVC) peak torque and percent voluntary activation were evaluated. In “Experiment #2”, participants performed 20 consecutive MVCs while surface electromyographic signals were detected from the vastus lateralis. Subjective assessments of energy and perceived exertion were examined.

Results

The interventions had no effect on strength or voluntary activation, but energy levels increased following treatments (p = 0.016, η2 = 0.257). Neither treatment influenced neuromuscular fatigue. Though some variables showed moderate-to-large effect sizes, these results were consistent for individuals with lower voluntary activation.

Conclusion

Placebo and OLP treatments had minimal influence on strength, voluntary activation, and fatigue resistance. As these findings differ from recent reports, we speculate that placebos and OLPs are more likely to enhance muscle function in patient populations seeking medical care.

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Abbreviations

ANOVA:

Analysis of variance

OLP:

Open-label placebo

MVC:

Maximal voluntary isometric contraction

RMS:

Root-mean-squared

ITT:

Interpolated twitch technique

EET:

Electrically evoked torque

EMG:

Electromyographic

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Authors and Affiliations

Authors

Contributions

AS, DF, JS, and MS conceived and designed the research. AS, RM, DK, and MS conducted the laboratory experiments. AS, RM, DK, and MS analyzed the data. AS and MS wrote the manuscript. All the authors read and approved of the final manuscript.

Corresponding author

Correspondence to Matt S. Stock.

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Conflict of interest

All investigators declared no conflicts of interest in the reporting of this research.

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Communicated by William J. Kraemer.

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Swafford, A.P., Kwon, D.P., MacLennan, R.J. et al. No acute effects of placebo or open-label placebo treatments on strength, voluntary activation, and neuromuscular fatigue. Eur J Appl Physiol 119, 2327–2338 (2019). https://doi.org/10.1007/s00421-019-04219-1

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  • DOI: https://doi.org/10.1007/s00421-019-04219-1

Keywords

  • Open-label placebo
  • Placebo
  • EMG
  • Muscle activation