Joints

Your joint encyclopedia — anatomy, range of motion, actions, and injury prevention for every major joint

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🎯 Overview

This section covers the 8 major joint complexes relevant to training. Each page gives you everything you need to understand joint function, assess mobility, and train safely.

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🦴 Joint Complexes

Upper Body

Upper Body Joints

Joint	Type	Degrees of Freedom	Primary Actions
Shoulder	Ball-and-socket	3	Flexion, extension, abduction, rotation
Elbow	Hinge + Pivot	2	Flexion, extension, pronation, supination
Wrist	Condyloid	2	Flexion, extension, radial/ulnar deviation

Mobility Priority

The shoulder needs mobility; the elbow needs stability. Don't stretch where you need stiffness.

Spine

Spinal Joints

Region	Vertebrae	Primary Motion	Common Issues
Cervical	C1-C7	Rotation, flexion/extension	Neck pain, forward head
Thoracic	T1-T12	Rotation	Kyphosis, stiffness
Lumbar	L1-L5	Flexion/extension	Low back pain, disc issues

The spine is a series of joints, each with small movements that combine for significant total motion.

Training Principle

The lumbar spine should be stable; the thoracic spine should be mobile. Most people have this reversed.

Lower Body

Lower Body Joints

Joint	Type	Degrees of Freedom	Primary Actions
Hip	Ball-and-socket	3	Flexion, extension, abduction, rotation
Knee	Modified hinge	1 (+ rotation when flexed)	Flexion, extension
Ankle	Hinge + Gliding	1-2	Dorsiflexion, plantarflexion, inversion/eversion
Foot	Multiple	Variable	Pronation, supination, toe flexion

The Ankle-Hip Connection

Limited ankle dorsiflexion forces compensation at the knee and hip. Always check ankle mobility when assessing squat mechanics.

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📐 Understanding Joint Types

Joints are classified by structure and the movements they allow:

Type	Structure	Movements	Examples
Ball-and-Socket	Spherical head in cup	All planes + rotation	Shoulder, Hip
Hinge	Convex meets concave	Flexion/extension only	Elbow, Knee, Ankle
Pivot	Ring around process	Rotation only	Atlas/Axis (neck), Radioulnar
Condyloid	Oval in elliptical cavity	2 planes, no rotation	Wrist, MCP joints
Saddle	Two saddle-shaped surfaces	2 planes + some rotation	Thumb CMC
Plane/Gliding	Flat surfaces	Gliding/sliding	Intercarpal, Intertarsal

Why this matters:

• Joint type determines possible movements
• Training outside the joint's design causes injury
• Understanding joint type helps diagnose movement limitations

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📊 What Each Joint Page Includes

Every joint page follows the same structure for easy navigation:

Section	What You'll Find	Default State
⚡ Quick Reference	At-a-glance facts (type, bones, degrees of freedom)	Expanded
🦴 Anatomy	Structure, ligaments, key features	Expanded
📐 Range of Motion	Normal ROM values, limiting factors	Expanded
🎬 Joint Actions	Movements allowed, muscles responsible	Expanded
💪 Muscles Acting On It	Prime movers, synergists, stabilizers	Expanded
🧘 Mobility Work	Stretches, mobilizations	Collapsed
⚠️ Common Issues	Injuries, dysfunctions, causes	Collapsed
🔗 Related Joints	Joints in the kinetic chain	Collapsed
📚 Sources	Research references	Collapsed

Navigation

Click any section header to expand/collapse. Core information is expanded by default; reference material is collapsed.

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🔄 The Joint-by-Joint Approach

Developed by Gray Cook and Mike Boyle, this framework identifies joints that need mobility vs stability:

Joint	Primary Need	Common Dysfunction
Foot	Stability	Overpronation
Ankle	Mobility	Limited dorsiflexion
Knee	Stability	Valgus collapse
Hip	Mobility	Limited extension, rotation
Lumbar Spine	Stability	Excessive flexion/extension
Thoracic Spine	Mobility	Kyphosis, rotation loss
Scapula	Stability	Winging, poor positioning
Shoulder (GH)	Mobility	Limited rotation
Elbow	Stability	Valgus stress
Wrist	Mobility	Limited extension

Key Insight: Dysfunction at one joint creates compensation at adjacent joints. Limited hip mobility causes lumbar instability. Limited ankle mobility causes knee valgus.

→ See Movement Patterns for how this applies to training.

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⚡ Quick Joint Finder

By Pain Location

"My shoulder hurts"

• Top of shoulder → Shoulder (AC joint)
• Front of shoulder → Shoulder (anterior)
• Back of shoulder → Could be rotator cuff, scapular, or thoracic

"My back hurts"

• Upper back → Thoracic Spine
• Lower back → Lumbar Spine
• Pain down leg → Possible disc issue, see Spine

"My knee hurts"

• Front of knee → Knee (patellofemoral)
• Inside of knee → Knee (medial)
• Behind knee → Hamstring issue or Baker's cyst

By Exercise Problem

If you struggle with...	Check...
Deep squat	Ankle, Hip
Overhead press	Shoulder, Thoracic Spine
Deadlift lockout	Hip
Bench press shoulder pain	Shoulder
Knee cave in squat	Hip, Ankle

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📊 Section Status

Joint	Status	Notes
Shoulder	✅ Complete
Hip	✅ Complete
Knee	✅ Complete
Spine	✅ Complete
Elbow	📋 Planned
Wrist	📋 Planned
Ankle	📋 Planned
Foot	📋 Planned

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For Mo

When users report joint pain or movement limitations, reference this section to identify potential causes. Use the Joint-by-Joint approach to check adjacent joints for compensations. Direct users to the "Common Issues" section of the relevant joint page for specific guidance.