Introduction: The reliability of estimated motor unit parameters using spike triggered averaging (STA) of the surface electromyogram (sEMG) has not been tested thoroughly. We investigated factors that may induce amplitude bias in estimated motor unit action potentials (MUAPs) and shape variations.
Methods: An sEMG record was simulated. MUAPs were then estimated from the STA of the simulated EMG.
Results: Variations in MUAP duration led to under-estimation of real MUAP amplitude, while synchronized firing led to over-estimation of amplitude. Spurious firing resulted in over-estimation of the amplitude of small motor units but under-estimation of the amplitude of large ones. Variability in amplitude and high firing rates had minimal influence on amplitude estimation. High firing rates and variation in MUAP duration led to large variations in MUAP shape. Estimation errors also correlated with shape variations.
Conclusions: Recommendations to enhance the accuracy of the STA estimates have been proposed.
Keywords: Spike triggered average; action potential amplitude variation; action potential classification; duration variation; firing rate; synchronized firing.
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