Assessment and sensitivity analysis of a motor units recruitment model during isometric contractions of the Biceps Brachii

The purpose of this study is to evaluate parameters impacting the Motor Units (MUs) recruitment during isometric contractions. For this purpose, a MUs recruitment scheme extracted from a multi-layered cylinder analytical upper limb model is used. This model generates a High-density surface electromyogram (HD-sEMG) signals. The approach consists to assess the influence of each parameter involved in the recruitment pattern model using a global sensitivity analysis method (GSA). The assessment of this model explores the effect of gender and ageing on the recruitment of MUs. Simulations with 150 different muscle anatomies and 150 different motor unit recruitment patterns were computed at five contractions levels 20%, 40%, 50%, 60% and 70% of the maximal voluntary contraction (MVC). Four subjects' categories were studied: Young and Elder men, and Young and Elder women. The obtained results show that the recruitment range slope (RR_slope) is the most sensitive parameter compared to parameters related to the MUs (repartition, size, number) for all contractions levels and for all categories. Furthermore, result shows that considering a fixed value for this parameter for all subjects' categories is not reliable.