A client who uses the erector spinae to perform a hip extension is exhibiting which...

Synergistic dominance occurs when synergist muscles compensate for a weak or inhibited prime mover, taking over its primary function. In this case, the erector spinae—normally a spinal stabilizer—are performing hip extension instead of the gluteus maximus, which is the prime mover for that action.

The NASM CPT7 Study Guide explains that altered length–tension relationships and poor neuromuscular recruitment patterns can cause helper muscles to dominate, leading to inefficient movement and potential injury.

This is distinct from reciprocal inhibition (agonist-antagonist relationship), autogenic inhibition (GTO-mediated relaxation), and neuromuscular efficiency (optimal recruitment patterns).