Abdominal hollowing and bracing strategies increase joint stability in the trunk region during sudden support surface translation but not in the lower extremities

BACKGROUND AND OBJECTIVE: Application of hollowing and bracing, abdominal activation strategies (AAS), has focused on improving trunk stability. This study aimed to clarify the AAS effect on body sway during support surface translation while standing. MATERIALS AND METHODS: Twenty healthy subjects (10 male, 10 female; aged 25.45 ± 3.22 years) performed hollowing, bracing, and natural strategies while standing, and exerted to maintain their balance during forward and backward translation. Ultrasonography evaluations confirmed the appropriate application of the 3 strategies by measuring abdominal muscle thickness. Additionally, a motion analysis system was used to capture the whole body sway along the sagittal plane. RESULTS: During backward translation, angular displacements of the trunk were significantly different among the 3 strategies (upper thoracic: F = 13.758, p < 0.001; lower thoracic: F = 8.477, p = 0.001; and lumbopelvis: F = 8.651, p = 0.001). AAS significantly decreased the sway by 25-36% in all inter-spinal segments compared with the natural strategy (p < 0.05). During forward translation, only angular displacement of the lower thoracic was significantly different among the 3 strategies (F = 7.640, p = 0.002), and bracing decreased the sway by 33.48% compared with the natural strategy (p = 0.003). No significant differences were seen between hollowing and bracing during forward and backward translation. CONCLUSIONS: AAS increased joint stability only in the trunk where joints are adjacent to abdominal muscles, but not in the lower extremities. The low impact of AAS on the lower extremities might have important implications on the paradigm of standing balance.