Are Extensor Digitorum Brevis and Gastrocnemius Working Together? Surface EMG Analysis in Healthy Children

Abstract

A relationship between intrinsic and extrinsic foot muscles is acknowledged during walking. Literature on foot-muscle recruitment in children is not very extensive. Purpose of the study was the surface-EMG-based evaluation of possible concomitant recruitment of intrinsic and extrinsic foot muscles during healthy-children walking. Gastrocnemius lateralis (GL) was analyzed as representative for extrinsic foot muscles (ankle plantar flexor). Extensor digitorum brevis (EDB) is one of the main intrinsic foot muscles, controlling foot movement and stability. In this study, EDB was considered as representative of foot muscles. Surface-EMG signals during 4-min walking trial were acquired in eight healthy school-age children (mean ± SD: age 8.3 ± 1.7 years; height 136 ± 8 cm; mass 30.9 ± 6.2 kg) to fulfill the goal of the study. Then, Statistical gait analysis, a recent methodology performing a statistical characterization of gait, was applied to process EMG data. An exceptional number of strides were analyzed to consider the expected variability (mean ± SD = 265 ± 30 strides for each child, nearly 2500 in total). The research was undertaken in compliance with ethical principles of Helsinki Declaration and approved by institutional expert committee. Results showed that EDB activity is localized in two separate regions of gait cycle: mid-stance (from 8.2 ± 7.0 to 50.3 ± 15.0% of gait cycle) and swing phase, from 73.8 ± 13.8 to 95.1 ± 4.7%. Main GL activity occurred in the same regions: mid-stance (from 5.7 ± 2.5 to 49.7 ± 4.6% of gait cycle) and swing phase, from 69.2 ± 18.7 to 95.4 ± 5.4%. These findings showed that regions of activity of EDB and GL were practically overlapped, suggesting that EDB and GL worked synergistically for foot and ankle-joint control in children walking, in a large percentage of strides. Present study produced novel data on the variability of the reciprocal role of EDB and GL during children walking, providing a deeper insight in mechanisms regulating ankle-foot stability.