A Lempel–Ziv complexity measure for muscle fatigue estimation

This paper presents a Lempel–Ziv complexity measure for analysis of surface electromyography signals. The Lempel–Ziv measure provides a metric for the number of distinct deterministic patterns and the rate of their creation in signals. We propose a ternary Lempel–Ziv measure, improving upon the binary Lempel–Ziv measure, and making it more suited for the analysis of biological signals. The Lempel–Ziv measure is evaluated with a muscle fatigue experiment in which participants perform static, cyclic, and random contractions. Results show this complexity measure shows a greater correlation to a steadily increasing muscle fatigue level compared to the conventional median frequency. This measure is computationally easy to compute and does not require power spectrum estimation and signal stationarity assumptions.