EMG Explained: What Does Electromyography Really Measure?

Electromyography (EMG) is widely used to study muscle activation and neuromuscular function — but what does a surface EMG signal actually tell us? And does a larger EMG amplitude really mean more force, more motor-unit recruitment, or even more muscle growth? In this evidence-based MiniLecture, I explain how surface electromyography (sEMG) works, where the EMG signal comes from, and how it should — and should not — be interpreted. Topics covered: 00:00 Introduction 01:20 What does an EMG signal actually measure? 08:09 Why does raw EMG fluctuate above and below zero? 13:00 Why does EMG amplitude increase with force demand? 15:20 EMG, muscle force and fatigue 16:45 Can acute EMG predict muscle hypertrophy? 25:19 Why normalize EMG to an MVC? 22:00 What can high-density EMG tell us? I also discuss an important practical question from resistance-training research: Does higher acute EMG mean greater hypertrophy? A longitudinal comparison of hip thrusts and back squats provides a particularly useful example of why acute surface-EMG amplitude should not be treated as a simple quantitative measure of the hypertrophic stimulus. Key message: EMG is an extremely powerful tool for studying neuromuscular function — provided that the physiological question matches what the measurement can actually tell us. A practical Lab-Talk on how we record and analyse surface EMG in the laboratory will follow. SCIENTIFIC REFERENCES [1] Clancy EA, Morin EL, Hajian G, Merletti R. Tutorial. Surface electromyogram (sEMG) amplitude estimation: best practices. J Electromyogr Kinesiol. 2023;72:102807. doi:10.1016/j.jelekin.2023.102807. [2] Besomi M, Hodges PW, Clancy EA, van Dieën JH, Hug F, Lowery M, et al. Consensus for experimental design in electromyography (CEDE) project: amplitude normalization matrix. J Electromyogr Kinesiol. 2020;53:102438. doi:10.1016/j.jelekin.2020.102438. [3] Besomi M, Hodges PW, van Dieën JH, Carson RG, Clancy EA, Disselhorst-Klug C, et al. Consensus for experimental design in electromyography (CEDE) project: electrode selection matrix. J Electromyogr Kinesiol. 2019;48:128-144. doi:10.1016/j.jelekin.2019.07.008. [4] Dick TJM, Tucker K, Hug F, Besomi M, van Dieën JH, Enoka RM, et al. Consensus for experimental design in electromyography (CEDE) project: application of EMG to estimate muscle force. J Electromyogr Kinesiol. 2024;79:102910. doi:10.1016/j.jelekin.2024.102910. [5] Muceli S, Merletti R. Tutorial. Frequency analysis of the surface EMG signal: best practices. J Electromyogr Kinesiol. 2024;79:102937. doi:10.1016/j.jelekin.2024.102937. [6] Vigotsky AD, Halperin I, Trajano GS, Vieira TM. Longing for a longitudinal proxy: acutely measured surface EMG amplitude is not a validated predictor of muscle hypertrophy. Sports Med. 2022;52(2):193-199. doi:10.1007/s40279-021-01619-2. [7] Plotkin DL, Rodas MA, Vigotsky AD, McIntosh MC, Breeze E, Ubrik R, et al. Hip thrust and back squat training elicit similar gluteus muscle hypertrophy and transfer similarly to the deadlift. Front Physiol. 2023;14:1279170. doi:10.3389/fphys.2023.1279170. [8] Karacan I, Türker KS. A comparison of electromyography techniques: surface versus intramuscular recording. Eur J Appl Physiol. 2025;125(1):7-23. doi:10.1007/s00421-024-05640-x. [9] Lecce E, Casolo A, Nuccio S, Felici F, Bazzucchi I. Analysis of motor units with high-density surface electromyography: methodological considerations and physiological significance. Eur J Appl Physiol. 2026;126(1):61-86. doi:10.1007/s00421-025-05996-8. [10] Sena CM. Integrating electromyography into the physiology curriculum. Adv Physiol Educ. 2026;50(1):261-279. doi:10.1152/advan.00237.2024. #EMG #Electromyography #MuscleActivation #ExercisePhysiology #SportsScience