Kinesiology

Lesson 9 of 16

Chest and abdomen

Chest and abdominal muscles move the trunk, support pressure regulation, and contribute to breathing and force transfer. Their actions vary with whether the ribs, pelvis, or limbs are fixed. Respect privacy and boundaries in these regions, explain draping, and obtain explicit consent before any area-specific work. Use gentle observation rather than interpreting abdominal appearance as a diagnosis.

Key points

• Pectoralis major acts on the humerus and can assist forced inspiration when the upper limb is fixed.
• Pectoralis minor acts on the scapula and may assist rib elevation when the scapula is fixed.
• Rectus abdominis flexes the trunk and helps manage abdominal pressure.
• Obliques rotate or side-bend the trunk, with different contributions by side and fiber direction.
• Transversus abdominis contributes to trunk stiffness and abdominal-wall tension.
• A relaxed position and clear consent are essential before chest or abdominal contact.

Key terms

Pectoralis major

O: medial clavicle, sternum, and upper costal cartilages; I: lateral lip of intertubercular groove; A: adducts and medially rotates arm, assists flexion.

Pectoralis minor

O: ribs 3-5; I: coracoid process; A: draws scapula anteriorly/inferiorly and may assist inspiration with scapula fixed.

Rectus abdominis

O: pubic crest and symphysis; I: xiphoid process and costal cartilages 5-7; A: flexes trunk and compresses abdomen.

External oblique

O: external surfaces of lower eight ribs; I: linea alba, pubis, and iliac crest; A: flexes trunk, ipsilaterally side-bends, contralaterally rotates.

Transversus abdominis

O: lower costal cartilages, thoracolumbar fascia, iliac crest, and inguinal ligament; I: linea alba and pubis; A: compresses abdomen and supports trunk stiffness.