Table 1 Measurement positions and measurement sites for trunk muscles

Rectus abdominis

Supine

3 cm lateral to the umbilicus

External oblique

Supine

2.5 cm anterior to the mid-axillary line, at the midpoint between the inferior rib and the iliac crest

Internal oblique

Supine

2.5 cm anterior to the mid-axillary line, at the midpoint between the inferior rib and the iliac crest

Transversus abdominis

Supine

2.5 cm anterior to the mid-axillary line, at the midpoint between the inferior rib and the iliac crest

Erector spinae

Prone

7 cm lateral to the L3 spinous process

Lumbar multifidus

Prone

2 cm lateral to the L4 spinous process

Psoas major

Prone

7 cm lateral from the L3 spinous process