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Muscle co-contractions are particularly relevant in analyzing children pathologies. To interpret surface electromyography (sEMG) in pathological conditions, reliable normative data in non-pathological children are required for direct comparison. Aim of the study was the quantification of co-contraction activity between quadriceps femoris (QF) and hamstring muscles during walking in healthy children. To this aim, Statistical gait analysis was performed on sEMG signals from rectus femoris (RF), vastus medialis (VM), and lateral hamstrings (LH), in 16401 strides walked by 100 healthy school-age children. Co-contractions were assessed as overlapping period between activation intervals of considered muscles. Results showed full superimpositions of LH with both RF and VL activity from terminal swing, 80-100% of gait cycle, to successive loading response (0-15% of gait cycle), in around 90% of strides, as reported in adults. This indicates that children regularly use a cocontraction activity between QF and hamstring muscles in weight acceptance during walking, supporting the hypothesis of a regulatory role of co-contraction in providing knee joint stability. Concomitant activity of QF and hamstring muscles was detected also during push-off phase (30-50% of gait cycle), showing a large variability intra and inter subjects and a lower occurrence frequency (around 25% of strides). This could be intended for controlling rapid knee flexion and/or stabilizing pelvis during body progression. Present findings represent the first attempt to provide normative sEMG dataset on variability of QF and hamstring muscles co-contractions during child walking, useful for discriminating physiological and pathological behavior and for designing future studies on maturation of gait. [ABSTRACT FROM AUTHOR]

The study was designed to assess the natural variability of the activation modalities of vastus medialis (VM) and vastus lateralis (VL) during walking at a self-selected speed and cadence of 30 young, healthy, females. This was achieved by conducting statistical gait analysis on the surface electromyographic signals from hundreds of strides for each subject. Results revealed variability in the number of activations, occurrence frequency, and onset-offset instants across the thousands of strides analyzed. However, despite the variability, there was one activation occurrence which remained consistent across subjects for both VM and VL. This occurred from terminal swing to the following loading response (observed in 100% of strides). A second, less frequent, activation occurred between mid-stance up to pre-swing (observed in 39.3 ± 22.4% of strides for VM and in 35.1 ± 20.6% for VL). No significant differences ( p > 0.05) were observed in the onset–offset instants or in the occurrence frequency, which suggest a simultaneous recruitment of VM and VL. This “normality” pattern represents the first attempt at developing a reference frame for vastii sEMG activity during walking, that is able to include the physiological variability of the phenomenon and control the confounding effects of age and gender. [ABSTRACT FROM AUTHOR]