Hypothesis testing with a computer model for force production in muscle

A computer model was designed based on the concept of common drive which suggests that motor units (group of muscle fibers and the single alpha-motoneuron that innervates them) in a muscle are controlled by a common input to the entire motoneuron pool. Where possible, the model utilized experimentally determined data and supplemented these with findings reported in the literature. It was validated by matching the simulated mean firing rates, power spectra, and compound muscle force outputs to that produced by data from the Tibialis Anterior muscle. The model was implemented using Matlab´s^® SIMULINK^® tool. In this form, the model allows easy modification of parameters to allow for virtual experimentation that would otherwise be impossible with human or animal models. The developed model was used to evaluate a commonly used technique, spike-triggered averaging (STA), to estimate the twitch force of an individual motor unit. It was concluded that STA has the potential to produce valid estimates only at firing rates below 3 pulses per second which are physiologically unfeasible. Simulations suggest that the effects of common drive on reliable MU twitch estimation may not be as extensive as initially expected. Additionally, hypotheses regarding the effect of various mechanical characteristics under certain physiological paradigms such as hand dominance or fatigue on the electrical properties can be investigated using the model.