Rodríguez Falces, JavierMalanda Trigueros, ArmandoMariscal Aguilar, CristinaRecalde Villamayor, SilviaNavallas Irujo, Javier2025-03-032025-03-032024-10-26Rodríguez-Falces, J., Malanda, A., Mariscal, C., Recalde, S., Navallas, J. (2024) The probability density function of the surface electromyogram and its dependence on contraction force in the vastus lateralis. BioMedical Engineering Online, 23, 1-17. https://doi.org/10.1186/s12938-024-01285-11475-925X10.1186/s12938-024-01285-1https://academica-e.unavarra.es/handle/2454/53642Introduction: the probability density function (PDF) of the surface electromyogram (sEMG) depends on contraction force. This dependence, however, has so far been investigated by having the subject generate force at a few fixed percentages of MVC. Here, we examined how the shape of the sEMG PDF changes with contraction force when this force was gradually increased from zero. Methods: voluntary surface EMG signals were recorded from the vastus lateralis of healthy subjects as force was increased in a continuous manner vs. in a step-wise fashion. The sEMG filling process was examined by measuring the EMG filling factor, computed from the non-central moments of the rectified sEMG signal. Results: in 84% of the subjects, as contraction force increased from 0 to 10% MVC, the sEMG PDF shape oscillated back and forth between the semi-degenerate and the Gaussian distribution; the PDF–force relation varied greatly among subjects for forces between 0 and ~ 10% MVC, but this variability was largely reduced for forces above 10% MVC; the pooled analysis showed that, as contraction force gradually increased, the sEMG PDF evolved rapidly from the semi-degenerate towards the Laplacian distribution from 0 to 5% MVC, and then more slowly from the Laplacian towards the Gaussian distribution for higher forces. Conclusions: the study demonstrated that the dependence of the sEMG PDF shape on contraction force can only be reliably assessed by gradually increasing force from zero, and not by performing a few constant-force contractions. The study also showed that the PDF–force relation differed greatly among individuals for contraction forces below 10% MVC, but this variability was largely reduced when force increased above 10% MVC.application/pdfeng© The Author(s) 2024. This article is licensed under a Creative Commons Attribution 4.0 International License.Filling factorGaussianityInterference pattern analysisProbability density function (PDF)Surface EMGinfo:eu-repo/semantics/article2025-03-03info:eu-repo/semantics/openAccess