Abstract

This paper studies the clinical use of a mathematical model for the simulation of electromyographic signals during submaximal and sustained contractions. Results from the mathematical model regarding electromyographic changes during these sustained contractions are validated with electromyographic changes during experimental fatiguing force contractions. Amplitude changes in the EMG were quantified as RMS changes and ACT changes. Variations in the frequency content were quantified as changes in the mean power frequency (MPF). The mathematical model made it possible to simulate all fatigue parameters described in the literature individually or combined. Motor unit characteristics and neural excitation parameters in the model were modified to simulate fatigue processes during sustained contractions. The basic reference signal for the analysis of sustained contractions was a 20% force contraction. The maximum excitation (75% vs 100% of tetanic excitation) assumed in the model did not have a significant effect on changes in the EMG parameters. High correlations and significant increases for RMS and ACT were observed with increasing force level (p<0.01). No significant decrease or increase was noticed in MPF with increased force levels (p>0.05). This was also reported from other experimental studies. A decrease in conduction velocity, decrease in peak firing rate, decrease in individual force capacity of motor units, changes in excitatory drive and probably synchronisation seem to be the major factors influencing muscular fatigue and related EMG parameters. In general, MPF decrease was similar to the decrease in the experimental study. RMS and ACT revealed higher values in simulated conditions compared with experimental conditions. It is intriguing that the ACT parameter increased during simulations, as it is only influenced by force level which was kept constant. In further research, looking at synchronisation between motor units might reveal part of the solution.