Three planes, in plain language
"Assessed in three planes" is on most of this website, so it is worth explaining properly rather than leaving it as a phrase.
The three directions
Every movement your body makes can be described as some mix of three directions.
- Forward and back. Walking, running, squatting, bending to pick something up. This is the one almost everybody trains.
- Side to side. Stepping sideways, leaning, reaching across your body, changing direction.
- Rotation. Turning. Throwing, swinging, twisting to look behind you, and every single step you take — walking is a rotational movement that happens to move you forwards.
Clinically those are the sagittal, frontal and transverse planes. The names matter less than the fact that there are three of them.
Why one is not enough
Gym equipment is mostly built for the first direction. Machines hold you still and let you push or pull forwards and back. That is useful for building strength and it is easy to measure, which is why it dominates.
The trouble is that very little of ordinary life or sport happens in one direction. You step off a kerb at an angle. You turn to catch something. You load a bag onto one shoulder and walk with it. If a joint has lost its range in rotation and you have only ever tested it forward and back, it will test perfectly well and still fail you on the field.
A knee that is strong in a straight line and uncontrolled in rotation is not a strong knee. It is a knee that has not been asked the question yet.
What it changes
Assessing in three planes mostly changes what you find. The exercises that come out of it often look fairly ordinary — a lunge, a step, a reach — but with the direction, the foot position or the arm path chosen deliberately, because that is the direction the assessment said was missing.
It also changes what "ready" means. Returning to sport is not a date on a calendar or a pain score. It is a set of things your body can do, in every direction the sport will demand, under enough load to be convincing.
