The between-day reliability of peroneus longus EMG during walking

The peroneus longus (PL) is a rearfoot evertor, important in frontal plane foot motion. Studying PL function has been limited by previous electromyography (EMG) studies reporting poor between-day reliability. Due to its close proximity to adjacent muscles, EMG measures of PL may be susceptible to crosstalk, thus correct electrode placement is vital. The aim of this study was to use ultrasound to aid placement of small surface EMG electrodes and determine the between-day reliability of PL EMG in healthy participants' walking. Ten participants walked barefoot and shod at a controlled, self-selected speed. Six trials per condition, per session, were recorded over two days (mean (SD): 5 (3) days apart). The muscle belly was located using ultrasound. EMG was recorded with surface electrodes (Trigno™ Mini, Delsys, Inc.) at 2000 Hz. Amplitude was normalized to the peak per gait cycle and time normalized to the gait cycle. Reliability of discrete variables were primarily assessed with the standard error of measurement (SEM), plus the coefficient of multiple correlation (CMC), the coefficient of variation (CV) and the intra-class correlation coefficient (ICC). The pattern of the EMG profile was consistent. The SEM of peak amplitude was 4% (3-8%) and 3% (2-5%) for barefoot and shod respectively. For timing of the peak the SEM was 2% (1-3%) and 1% (1-2%) for barefoot and shod respectively. Low SEM of discrete variables suggests good reliability of PL EMG during walking supporting the future use of this protocol. Therefore activation of PL can be confidently studied in repeated-measures study designs.