Different Smoothing Window Lengths can Estimate the Neuromuscular Fatigue Threshold at The same Intensity of the Lactate Threshold During the Leg Press Exercise

Runer Augusto Marson1, 2
, Nuno Manuel Frade de Sousa3
, Robson Dias Scoz4, 5, *
, Jose Joao Baltazar Mendes5
, Luciano Maia Alves Ferreira5
, Marco Aurélio Anunciação de Melo4, 7
, Vilmar Baldissera8
, Lucas Filgueiras Freitas4, 7
, César Ferreira Amorim4, 5, 6, 7

1 Instituto de Pesquisa da Capacitação Física do Exército, Rio de Janeiro, Brasil
2 Neuromuscular Research Laboratory & Warrior Human Performance Research Center, School of Health and Rehabilitation Sciences, University of Pittsburgh, Pittsburgh, PA, USA
3 Laboratório de Fisiologia do Exercício e Medidas de Avaliação, Faculdade Estácio, Vitória, Brasil
4 Programa de Mestrado e Doutorado em Fisioterapia, Universidade Cidade de São Paulo (Unicid), São Paulo, Brasil
5 Laboratório de Avaliação Física e Funcional em Fisioterapia (LAFFFi), Centro de Investigação Interdisciplinar Egas Moniz (CiiEM), Setúbal, Portugal
6 Laboratoire de Recherche BioNR, Université du Quebec, Saguenay, Canada
7 Lab Corinthians R9, Sport Club Corinthians Paulista, Sao Paulo, Brazil
8 Laboratório de Fisiologia do Exercício, Departamento de Ciências Fisiológicas da Universidade Federal de São Carlos (UFSCar), São Paulo, Brasil

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Creative Commons License
© 2023 Marson et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Programa de Mestrado e Doutorado em Fisioterapia, Universidade Cidade de São Paulo (Unicid), São Paulo, Brasil; Tel: +55 48991446644;



This study aimed to compare different smoothing window lengths used to compute the RMS and their impact on RMS slope during leg press exercise and to compare the RMS slope behavior with lactate threshold.


Twelve subjects performed an incremental test on a leg press machine where blood lactate concentration was measured at each stage. The RMS of vastus medialis (VM), vastus lateralis (VL) and rectus femuralis (RF) were computed for 200, 1500 and 3000ms windows length periods, and the RMS linear slope was used to interpret the results in the amplitude domain. The EMG fatigue threshold (EMGth) was determined for the quadriceps muscle during the three smoothing window lengths.


There was no significant difference (p> 0.05) in RMS slope between the three different RMS window length analyses for VM and VL muscles. The RMS slope was significantly higher (p ≤ 0.05) for the window length period of 1500 and 3000ms compared to 200ms in some intensities of exercise. The ICCs between the RMS slopes were 0.94 for RF and 0.95 for VL and VM. There was no significant difference (p> 0.05) between the EMGth at different window length periods and the lactate threshold (28.0 ± 3.7% of 1RM).


Different smoothing window lengths to computed RMS could be used during resistance exercise without differences in RMS slope. The smoothing window lengths don´t influence EMGth intensity and are related to the lactate threshold.

Keywords: Surface electromyography, Root mean square, Window length, Anaerobic threshold, Resistance exercise, Lactate threshold.