The joint-by-joint idea
The joint-by-joint approach, popularized by physical therapist Gray Cook and strength coach Michael Boyd, proposes that joints alternate up the kinetic chain in their primary need. The ankle is treated as a mobility joint, the knee as a stability joint, the hip as mobility, the lumbar spine as stability, the thoracic spine as mobility, and the scapula and glenohumeral joint as a blend leaning toward mobility with controlled stability.
It is a coaching heuristic rather than a strict anatomical law. Every joint actually needs both qualities; the model simply highlights which quality tends to be the limiting factor when movement breaks down.
Why coaches map it this way
The pattern reflects what often goes wrong in practice. Stiff ankles and hips push extra demand onto the knee and low back, which are built to transmit load more than to move freely. Framing each joint by its dominant need gives a quick checklist for where to look when a movement looks compensated.
How to use it sensibly
Treat the continuum as a starting hypothesis, not a diagnosis. Individual anatomy, training history, and injury all shift where someone sits on the mobility-to-stability scale. This is general educational information about a training framework, not medical advice; a qualified clinician should assess persistent joint pain or restriction.