Differential Activation of the Multifidus and Erector Spinae During Asymmetric Spinal Stabilizing Exercise in...

To identify the asymmetric spinal stabilizing exercise (ASSE) postures that selectively activate the multifidus (Mu) relative to the erector spinae (ES) in patients with adolescent idiopathic scoliosis (AIS), thereby supporting the development of curve-specific exercise programs for three-dimensional spinal deformities.

Surface electromyography recordings were obtained bilaterally from the ES and Mu muscles during ASSE postures. Signals were normalized to the maximal voluntary isometric contraction. The asymmetry ratio, Mu/ES ratio, and additional asymmetric contraction of the Mu were analyzed.

The study included 40 patients with AIS. The Mu demonstrated greater ipsilateral activation in the side-lying posture, whereas greater contralateral activation was observed during unilateral lower extremity lifting and combined upper-lower extremity lifting in the prone posture, as well as during combined upper-lower extremity lifting in the bird-dog posture. In the prone and bird-dog postures, the Mu/ES ratio exceeded 1.0, indicating relatively stronger Mu recruitment under rotational loading. Additional asymmetric contraction of the Mu was greatest in the side-lying posture (47%), with differences<15% in all other postures.

ASSE induces posture-specific asymmetric activation of the paraspinal muscles in patients with AIS. Although the side-lying posture produced the largest asymmetry, this reflected increased ES activity for trunk elevation rather than true selective Mu contraction. In contrast, the prone and bird-dog postures demonstrated a greater Mu contribution relative to the ES under rotational loading. These findings suggest that ASSE can be adapted to target specific paraspinal muscle components: side lying for lateral bending and bird-dog variations to enhance rotational stability.