Standardizing fatigue-resistance testing during electrical stimulation of paralysed human quadriceps muscles, a practical approach

Martin Schmoll (1, 2) , Ronan Le Guillou (2, 1) , David Lobato Borges (3) , Charles Fattal (4) , Emerson Fachin-Martins (3) , Christine Azevedo Coste (2, 1)

1 UM - Université de Montpellier
2 CAMIN - Contrôle Artificiel de Mouvements et de Neuroprothèses Intuitives
3 UnB - Universidade de Brasilia [Brasília]
4 CRRF - Centre de Rééducation et de Réadaptation Fonctionnelles de La Chataigneraie [Menucourt]

Background: Rapid onset of muscular fatigue is still one of the main issues of functional electrical stimulation (FES). A promising technique, known as distributed stimulation, aims to activate sub-units of a muscle at a lower stimulation frequency to increase fatigue-resistance. Besides a general agreement on the beneficial effects, the great heterogeneity of evaluation techniques, raises the demand for a standardized method to better reflect the requirements of a practical application. Methods: This study investigated the fatigue-development of 6 paralysed quadriceps muscles over the course of 180 dynamic contractions, evaluating different electrode-configurations (conventional and distributed stimulation). For a standardized comparison, fatigue-testing was performed at 40% of the peak-torque during a maximal evoked contraction (MEC). Further, we assessed the isometric torque for each electrode-configuration at different kneeextension-angles (70°-170°, 10° steps). Results: Our results showed no significant difference in the fatigue-index for any of the tested electrode-configurations, compared to conventional-stimulation. We conjecture that the positive effects of distributed stimulation become less pronounced at higher stimulation amplitudes. The isometric torque produced at different knee-extension angles was similar for most electrode-configurations. Maximal torque-production was found at 130°-140° kneeextension-angle, which correlates with the maximal knee-flexion-angles during running. Conclusion: In most practical applications, FES is intended to initiate dynamic movements. Therefore, it is crucial to assess fatigue-resistance by using dynamic contractions. Reporting the relationship between produced torque and knee-extension-angle can help to observe the stability of a chosen electrode-configuration for a targeted range-ofmotion. Additionally, we suggest to perform fatigue testing at higher forces (e.g. 40% of the maximal evoked torque) in pre-trained subjects with SCI to better reflect the practical demands of FES-applications.

Mots clés: Dynamic movement; Fatigue testing; Functional electrical stimulation; Distributed stimulation; Spinal cord injury; Knee dynamometer

Domaines: Automatique / Robotique

Martin Schmoll, Ronan Le Guillou, David Lobato Borges, Charles Fattal, Emerson Fachin-Martins, et al.. Standardizing fatigue-resistance testing during electrical stimulation of paralysed human quadriceps muscles, a practical approach. Journal of NeuroEngineering and Rehabilitation, 2021, 18 (11), ⟨10.1186/s12984-021-00805-7⟩. ⟨hal-03118295⟩