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Longing for a Longitudinal Proxy: Acutely Measured Surface EMG Amplitude is not a Validated Predictor of Muscle Hypertrophy

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Abstract

Surface electromyography amplitudes are commonly measured in acute sports and exercise science studies to make inferences about muscular strength, performance, and hypertrophic adaptations that may result from different exercises or exercise-related variables. Here, we discuss the presumptive logic and assumptions underlying these inferences, focusing on hypertrophic adaptations for simplicity’s sake. We present counter-evidence for each of its premises and discuss evidence both for and against the logical conclusion. Given the limited evidence validating the amplitude of surface electromyograms as a predictor of longitudinal hypertrophic adaptations, coupled with its weak mechanistic foundation, we suggest that acute comparative studies that wish to assess stimulus potency be met with scrutiny.

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Notes

  1. By sEMG amplitudes, we refer to statistics summarizing the average degree of variation of the amplitude of the raw sEMG over a given period into a single value, with the most popular estimate being the root mean square amplitude.

  2. Similar findings have been reported in other studies and muscles [4,5,6,7,8,9,10,11].

  3. Changing a muscle’s state over time (e.g., dynamic contractions or changes in force) will complicate the otherwise straightforward neuromuscular excitation-muscle state relationship [2, 21]. Although this process can be modeled, it is typically not in applied sEMG studies in sports science.

  4. Morton et al. [23] also demonstrate that sEMG amplitudes can be decoupled from (a) muscle state changes, as measured via muscle glycogen depletion, which spans Premises 1 and 2, and (b) anabolic signaling, which spans Premises 1–3. However, the authors employed between- rather than within-subject correlations. Here, we think the more relevant question is the within-subject relationship (see [24]), which may be a fruitful avenue for future research.

  5. For a more complete and nuanced detailing of the MPS-hypertrophy relationship, we direct readers to the recent review by Witard et al. [27].

  6. We also acknowledge the \(T_2\)-weighted magnetic resonance imaging (MRI) and regional hypertrophy work by Wakahara et al. [59,60,61] in the triceps brachii and quadriceps and Illera-Dominguez et al. [62] in the hamstrings, quadriceps, and adductors. Despite their mixed findings, there are two caveats to note. Principally, this work used MRI rather than sEMG; to our knowledge, MRI has not been validated against sEMG for intramuscular heterogeneity. Secondly, these studies did not model within-subject relationships directly.

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Correspondence to Andrew D. Vigotsky.

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This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1324585.

Author's contributions

ADV and IH devised the paper and wrote the first draft. ADV, IH, GST, and TMV edited the manuscript for content and clarity and approved the final version for publication.

Acknowledgements

We would like to thank David Behm, Thiago Torres da Matta, Roger Enoka, Franco Impellizzeri, Greg Lehman, Robert Morton, Jeff Nippard, Greg Nuckols, Stu Phillips, Brad Schoenfeld, James Steele, Nicolas Place, and Jim Potvin for their thoughtful comments and feedback.

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Vigotsky, A.D., Halperin, I., Trajano, G.S. et al. Longing for a Longitudinal Proxy: Acutely Measured Surface EMG Amplitude is not a Validated Predictor of Muscle Hypertrophy. Sports Med 52, 193–199 (2022). https://doi.org/10.1007/s40279-021-01619-2

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