Table 1. Trunk Muscle Training Program.

Muscle Group	Importance of Muscle	Examples of Exercise Progression
Transversus Abdominus	Draws in abdominal wall, increases intra abdominal pressure w/o flexing the trunk TrA may activate in a feed-forward mechanism to stabilize the trunk for extremity motions³⁷	Abdominal Bracing in supine>> Bracing in hook-lying with leg movements>> Bracing in hook-lying with bridging>> Abdominal Bracing in standing Possible Substitutions: holding breath
Erector Spinae/Multifidus	Extend the spine Segmental extensors co-contract w/ antero-lat. abdominals to stabilize trunk	Single arm or leg lifts-standing with elbows leaning on counter>> Opposite arm and leg lifts standing with elbows on counter >> Single arm or leg lifts-prone over bolster^{35, 60}>> Opposite arm and leg lifts-prone over bolster>> Same exercises performed in quadruped
Rectus Abdominus	Primary flexor of the trunk	Curl ups as described by McGill^35--careful to maintain neutral spine and avoid excessive flexion
Oblique Abdominals	Co-contracts w/ multifidus for trunk stabilization, generates side-bending and rotation forces in trunk Obliques activate in anticipation of extremity movement	Remedial side bridge against wall>> Remedial side bridge with leg lift on floor/bed Horizontal side bridge (hips and knees fully flexed >> knees flexed >> knees extended)^{35, 61}
Quadratus Lumborum	Suggested to be the primary stabilizer of side-bending movements³⁵	Same as above for obliques