TABLE 1.

Placement of surface electromyography electrodes and measurement of the maximum voluntary contraction of trunk muscles.

Muscle	Placement of electrodes	Maximum voluntary contraction test
Rectus abdominis	3 cm lateral to the umbilicus	Participants were in the supine position with knees bent and feet flat and were asked to flex against manual resistance at the shoulders
External oblique	15 cm lateral to the umbilicus	Participants were in the supine position with knees bent and feet flat and were asked to laterally bend and axially twist against manual resistance at the shoulders
Erector spinae	3 cm lateral to the L3 spinous process	Participants were in the prone position. Then, trunk extension was performed against manual resistance at the shoulders
Lumbar multifidus	3 cm lateral to the L5 spinous process	Test was the same as the test of the erector spinae muscle