Motor unit double discharges, or doublet firings, have been described as two consecutive motor unit discharges that occur with short interspike intervals. By the use of electrical stimulation protocols, short interspike intervals inserted at the beginning of a stimulation train have been shown to increase both the peak force and the rate of rise of force production [S.J. Garland and L. Griffin, Motor unit double discharges: statistical anomaly or functional entity? Can. J. Appl. Physiol. 24 (1999), pp. 113–130]. The aim of this article is to estimate possible mechanical effects of simulated motor unit doublets in selected motor unit pools (MUPs) during the initial isometric contractions. Five different MUPs with varying ranges were simulated considering important nonlinearities in the force response to pairs of stimuli according to Thomas et al. [C.K. Thomas, R.S. Johansson, and B. Bigland-Ritchie, Pattern of pulses that maximize force output from single human thenar motor units. J. Neurophysiol. 82 (1999), pp. 3188–3195]. The results support the hypothesis that double discharges represent a functional entity: expected increases depend on the properties of the MUP as a whole. Relative timing of the doublet discharges occurs, but has only little effect.
Mathematical and Computer Modelling of Dynamical Systems
Methods, Tools and Applications in Engineering and Related Sciences
Volume 16, 2010 - Issue 5: Selected examples in biomechanical modelling and simulation
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