An Accurate Biceps Muscle Model with sEMG and Muscle Force Outputs
Katherine Anne Wheeler,
Dinesh Kant Kumar,
A differential, time-invariant, surface electromyogram (sEMG) model has been implemented. The model uses realistic physiological parameter values to simulate both electrical sEMG and muscle force output signals. The combination of these signals is used to validate the accuracy of the model with respect to experimental results. The novelty of this sEMG model implementation is that it assigns more realistic distributions of variables to create life-like motor unit (MU) characteristics and defines individual parameter values to type I and type II muscle fiber types. Variables such as muscle fiber conduction velocity, jitter (the change in the inter-pulse interval between subsequent action potential firings) and motor unit size have been considered to follow normal distributions about mean values reported by experts in the field. In addition, motor unit firing frequencies have been considered to have non-linear and type-based distribution that is in accordance with reported experimental observations. Motor unit recruitment is also related to the motor unit type. The model has been simulated to predict single-channel differential sEMG signals and force outputs from voluntary, isometric contractions of the biceps brachii muscle. This model has been experimentally verified by conducting experiments on ten participants who performed isometric contractions of the biceps brachii at three different force levels. Signal features of the simulated signals were compared with experimental results, and it has been shown that the RMS of the sEMG increases linearly with contraction strength in both cases, despite the non-linearity of some simulation parameters. The simulated sEMG signals show similar values and rates of change of RMS to the experimental signals. To verify the accuracy of the model, the force output was simulated at varying contraction levels. This simulated force increased linearly at a comparable rate to the experimental force exerted.