Mechanical function of major joints

Understand how major joints bend, rotate, lock, and glide within their mechanical limits.

What it is

You identify the possible, limited, and impossible movements of each major joint. You distinguish hinge, rotational, and gliding movements between bones.

In poses, you show movement through the correct joints. An arm lift includes shoulder rotation, and a crossed leg uses hip movement with pelvic rotation while the knee bends correctly.

You picture the bones within a pose and track how one joint affects the next. This supports invented poses that remain mechanically possible with limited reference.

Why it matters

Joint mechanics support physically possible figure poses. Weak control can produce elbows or knees bending incorrectly, shoulders reaching beyond their structure, or hips remaining fixed while the legs move. Clothing folds and muscle forms may then conflict with the skeleton.

You can check it when

• ✓Sketch a stick figure in varied poses and mark how each major joint bends without accidental double joints.
• ✓Reduce a complex pose to bones and label which joints hinge, rotate, or glide, including the approximate range of each movement.
• ✓Check invented poses for stable, mechanically possible joint positions without hiding joints behind props or crops.

Related skills

• Torso dynamics (directions of torso and pelvis; rib cage–pelvis relationship)
• Muscle changes during movement
• Figure in space (perspective, foreshortening, mental rotation)
• Weight, balance, and contrapposto
• Hand construction (palm, fingers, thumb mechanics)
• Quadruped foundation (skeleton, major muscle groups)