Abstract
Research demonstrates that the magnitude of torque variability is influenced by joint angle. However, complexity-based measures seem to provide distinct information than the traditional magnitude-based measures of variability, being more sensitive to detect subtle changes in physiological outputs’ dynamics. Therefore, this study aimed to investigate the effect of joint angle on torque complexity and intermuscular coordination. Twenty-five male adults performed a sustained isometric knee extensor task at 110% of their end-test torque for 30 s at five different joint angles. Torque complexity and variability were assessed using Sample Entropy (SampEn) and Coefficient of Variation (CV), respectively, while intermuscular coordination was evaluated through Co-Contraction Index (CCi). Results revealed that SampEn at OA−30º was significantly lower than at OA (p = 0.014) and OA + 15º (p = 0.022), indicating reduced torque complexity at shortened muscle lengths. CV and CCi exhibited similar behaviors by presenting a trend for a U-shape relationship with joint angle. Our findings suggest a decrease in the individuals’ capacity to regulate the torque production with the shortening of the knee extensors which can possibly be explained by the mechanical properties of the muscle and central and peripheral neuromuscular factors or, most importantly, by the complex interaction between all the mechanisms involved in torque regulation.
Data availability
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.
Code availability
All Matlab® R2023a codes are deposited in Zenodo repository [65] and available on reasonable request.
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Acknowledgements
This work was supported by FCT - Fundação para a Ciência e Tecnologia, I.P. by project referenceUID/4585/2025 (https://doi.org/10.54499/UID/04585/2025) . João R. Vaz was partly supported by the Fundação para a Ciência e Tecnologia, I.P. under grant number UIDB/00447/2020 to CIPER - Centro Interdisciplinar para o Estudo da Performance Humana (unit:447). João R. Vaz was partly funded by Fundação para a Ciência e Tecnologia through Egas Moniz Center for Interdisciplinary Research (CiiEM) under grant number UIDB/04585/2020. João H. Oliveira, João S. Gomes and Philipp Bauer were supported with PhD scholarships from Fundação para a Ciência e Tecnologia with grant numbers 2021.08271.BD, 2022.10952.BD and UI/BD/154379/2023, respectively.
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J.H.O.: Conceptualization, Methodology, Software, Validation, Formal Analysis, Investigation, Writing—Original Draft, Writing—Review and Editing, Visualization, Project administration; J.R.V.: Conceptualization, Methodology; Software, Validation, Formal Analysis, Resources, Data Curation, Writing—Original Draft, Writing—Review and Editing, Visualization, Supervision, Project administration; J.S.G.: Validation, Investigation, Writing—Review and Editing, Visualization; P.P.C.: Conceptualization, Methodology, Resources, Writing—Review and Editing, Visualization, Supervision, Project administration; Philipp Bauer: Validation, Writing—Review and Editing, Visualization.
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Oliveira, J.H., Gomes, J.S., Bauer, P. et al. Torque regulation is affected by joint angle during isometric contraction in young male adults. Sci Rep (2026). https://doi.org/10.1038/s41598-026-42754-y
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DOI: https://doi.org/10.1038/s41598-026-42754-y
