Data from: Physiological tremor reveals how thixotropy adapts skeletal muscle for posture and movement

People and animals can move freely, but they must also be able to stay
still. How do skeletal muscles economically produce both movement and
posture? Humans are well known to have motor units with relatively
homogeneous mechanical properties. Thixotropic muscle properties can
provide a solution by providing a temporary stiffening of all skeletal
muscles in postural conditions. This stiffening is alleviated almost
instantly when muscles start to move. In this paper, we probe this
behaviour. We monitor both the neural input to a muscle, measured here as
extensor muscle electromyography (EMG), and its output, measured as tremor
(finger acceleration). Both signals were analysed continuously as the
subject made smooth transitions between posture and movement. The results
showed that there were marked changes in tremor which systematically
increased in size and decreased in frequency as the subject moved faster.
By contrast, the EMG changed little and reflected muscle force requirement
rather than movement speed. The altered tremor reflects naturally
occurring thixotropic changes in muscle behaviour. Our results suggest
that physiological tremor provides useful and hitherto unrecognized
insights into skeletal muscle's role in posture and movement.