sEMG-based evaluation of muscle recruitment variability during walking in terms of activation length and occurrence frequency

Surface electromyography (sEMG) is commonly used in gait analysis for detecting muscle activity in a non-invasive way, preserving the normal mobility of the subject. The purpose of the study was to assess the variability of sEMG signals acquired from lower-limb muscles during walking. To this aim, a statistical analysis of sEMG signals from a large number (hundreds) of strides per subject was performed in twenty-two healthy young caucasian volunteers. Tibialis Anterior, Gastrocnemius Lateralis, Rectus Femoris, Biceps Femoris and Vastus Lateralis were selected to represent both proximal and distal leg segments. Besides the muscular activation onset-offset instants, the study was aimed to analysed the occurrence frequency of muscle recruitment, a parameter seldom considered because of the low number of strides usually analysed in classic EMG studies. Findings illustrated that a single muscle showed a different number of activation intervals in different strides of the same walking. The number of times when muscle activates during a single gait cycle defined the modality of muscle recruitment, that in the present study was referred to as activation modality, i.e. n-activation modality consists of n-activation intervals for the considered muscle, during a single gait cycle. For each of the selected muscles, five activation modalities were detected. Each of these activation modalities is characterized by a different occurrence frequency and by different onset-offset activation instants. Concomitance of these results indicates a large variability in onset-offset muscular activation and occurrence frequency, which should be considered in discriminating pathological from physiological behaviour and for designing focused gait studies.