Influence of the variability in motor unit discharge times and neural drive on force steadiness during submaximal contractions with a hand muscle

The fluctuations in force during steady submaximal contractions can be caused by either or both the variability in discharge times of individual motor units and in the neural drive. After careful alignment of the force and discharge times within an optimal bandwidth (0.75-5 Hz), the fluctuations in force at the lower target force were strongly correlated with both measures of variability, whereas those at the higher target force were best explained by the variability in neural drive.