Altered Peroneus Longus Activation Strategies in Male Athletes with Chronic Ankle Instability: Insights from Traditional and Spike Shape EMG Analyses.

Individuals with chronic ankle instability (CAI) show reduced peroneus longus (PL) activity during dynamic actions such as walking, running, and jumping. The strategy by which motor units (MUs) are activated in this dysfunction remains unclear, hindering targeted rehabilitation. We assessed PL electromyographic (EMG) activity during submaximal and maximal isometric foot pronation and plantar flexion (IFPPF), mimicking the biomechanical function of the PL during dynamic actions. Seventeen male athletes with CAI and 17 control athletes without CAI (CO) participated. From 1-s EMG signals recorded at 30 % and 100 % of maximal voluntary contraction (MVC) while performing IFPPF, traditional EMG parameters [root mean square (RMS), median frequency (MdF), and mean frequency (MF)] and spike shape analysis metrics [mean spike amplitude (MSA), mean spike frequency (MSF), mean spike duration (MSD), mean spike slope (MSS), and mean number of peaks per spike (MNPPS)] were analyzed. Compared with control athletes, those with CAI exhibited lower MdF, MF, and MSF and higher MSD and MNPPS at both 30 % and 100 % MVC-IFPPF, whereas MSS was reduced in CAI athletes only at 100 % MVC (p < 0.05). The observed decreases in MSF, along with higher MSD values in male athletes with CAI, may correspond to a reduced firing rate of PL motor units, which requires future verification using decomposition-based methods.