How Muscles Move Bones: Contraction, Not Pushing

Muscles only pull—they never push. Movement occurs through:

1. Contraction: Sarcomeres shorten → muscle pulls its insertion toward its origin.
2. Relaxation: Elastic recoil + antagonist contraction returns bone to start position.

Key Concepts

• Origin: Proximal/less mobile attachment.
• Insertion: Distal/more mobile attachment.
• Lever systems: Bones act as levers; joints are fulcrums; muscles provide effort.
• Agonist/antagonist pairs: Biceps (flexion) vs. triceps (extension).

Types of Contraction

• Concentric: Muscle shortens under load (lifting).
• Eccentric: Muscle lengthens under tension (lowering).
• Isometric: Tension without length change (holding).

This pull-only mechanism underlies all voluntary movement, posture, and respiration.