How is trunk extensor strength evaluated in manual muscle testing (MMT)?

How is trunk extensor strength evaluated in manual muscle testing (MMT)?

• A. Seated row with resistance
• B. Prone, raise the upper trunk off the table or hold extension against resistance; stabilize the pelvis
• C. Supine, perform knee extensions
• D. Prone with hip flexion

Answer: (B)

The key idea is isolating the spinal extensor muscles (the trunk extensors) during testing. In the standard trunk extensor MMT, the person lies face down (prone) and actively extends the spine to raise the upper trunk off the table, or the examiner resists this extension. The pelvis is held steady to prevent movement from the hips or lower back in a way that would recruit other muscles. This setup specifically targets the erector spinae and related back extensors, giving a true read on their strength. Other positions don’t isolate these muscles. Seated rowing mainly tests muscles of the upper back and shoulder girdle in a seated posture, not the spinal extensors. Supine knee extensions primarily assess the quadriceps. A prone position with hip flexion would engage hip flexors and other compensatory movements rather than isolate the trunk extensors.

The key idea is isolating the spinal extensor muscles (the trunk extensors) during testing. In the standard trunk extensor MMT, the person lies face down (prone) and actively extends the spine to raise the upper trunk off the table, or the examiner resists this extension. The pelvis is held steady to prevent movement from the hips or lower back in a way that would recruit other muscles. This setup specifically targets the erector spinae and related back extensors, giving a true read on their strength.

Other positions don’t isolate these muscles. Seated rowing mainly tests muscles of the upper back and shoulder girdle in a seated posture, not the spinal extensors. Supine knee extensions primarily assess the quadriceps. A prone position with hip flexion would engage hip flexors and other compensatory movements rather than isolate the trunk extensors.