Meeting Abstract
The control process underlying a signal can be quantified by assessing features of variability using measures like Sample Entropy (SampEn). Evaluating the time scale at which transition between SampEn values reflecting order to those reflecting randomness occurs within a signal can quantify short-term fluctuations that describe adjustments in the underlying signal process and are applicable to studying neuromuscular function during motor tasks. Here we investigate whether changes in features of myoelectric signal structure occur in response to altered locomotor demand. Myoelectric signals were recorded from three ankle extensor muscles of rats running on a treadmill at nine velocity/incline combinations. Standardised total intensity time series of recorded signals were reshaped to provide increasingly larger time intervals between consecutive data points prior to SampEn calculation. The time scale at which SampEn transitioned from structured to random (Entropic Half Life, EnHL) quantified the time scale over which structure within the signal persisted. To ensure results reflected structure within recorded signals EnHL values were also determined for phase randomised surrogate signals. A significant effect of locomotor velocity on EnHL values occurred in each muscle. The longest EnHLs occurred at the fastest velocities. Incline also had a significant effect. The shortest EnHLs occurred for locomotion on 0o incline. EnHL values were significantly different between original and phase randomised signals indicating that phase related structure within them (i.e. the position of each of the data points in time) underpinned the EnHLs. Therefore, changes in EnHL reflect changes in underlying structure of recorded myoelectric signals. EnHL could have significant value as a novel marker of neuromuscular responses to changes in demand and intensity of a given motor task.
