Alternating needs up the body
The joint-by-joint approach, associated with Gray Cook and Mike Boyle, proposes that the body's joints tend to alternate in their primary need as you travel up the chain: some are biased toward mobility and others toward stability. The ankle is framed as wanting mobility, the knee stability, the hip mobility, the lumbar spine stability, the thoracic spine mobility, and so on.
The idea is a planning lens: it suggests where to look first when a movement feels restricted or strained, rather than a rigid rule that each joint does only one job.
Why neighbors compensate
A central observation is that when a joint that should be mobile becomes stiff, a neighboring joint that should be stable often takes up the slack and moves more than it should, which can concentrate stress there. Stiff hips, for instance, can lead the lower back to move more during bending and lifting.
The model is a simplification and the strict mobility-or-stability labels do not capture every joint's real demands, so it is best used as a starting framework. Treat persistent pain as a reason to see a qualified clinician rather than to self-diagnose. This is general educational information, not medical advice.