Core neuromuscular co-activation mechanisms partly explain trunk kinematics in a perturbed postural task

When facing a ground translation, trunk neuromuscular control remains unclear, despite its importance in sport practice, because core neuromuscular co-activations have not been investigated. Indeed, the spinal stiffness and trunk kinematics are impacted by core co-activation in dynamic tasks. Therefore, the aim of this study was to determine whether core neuromuscular co-activations could explain its motion during perturbed postural tasks.

Thirty-six athletes (handball, karate, long jump) performed a perturbed postural task, facing six medial ground translations in unipedal stance. Trunk and hip kinematics were recorded with inertial measurement units and rectus abdominis, external obliques and erector spinal were measured with surface electromyography (EMG). Trunk and hip joint angles, as well as directed co-activation ratio and co-activation index between left and right EMG signals, were computed from 100 ms prior to the start of the translation until 800 ms after. Moreover, core neuromuscular latencies and trunk amplitude were calculated.

Core muscles co-activation ratios varied according to trunk kinematics during the perturbation. Furthermore, earlier activation for agonists' muscles combined with larger activation compared to antagonists' muscles in the early phase of the perturbation were noticed (p < 0.05). Lastly, co-activation ratios might partially predict trunk amplitude (R² between 19.3% to 39.1%) when participants were facing a medial translation on single leg stance. Early lateral trunk flexions could be considered as active control mechanisms ensuring postural stability.

Overall, our results supported the active role of the core to maintain postural balance and underlined that the neuromuscular co-activation analysis is useful to provide a better understanding of core control.