This Osteopathic principle of ‘the body is a unit’ describes how you can not affect one part of the body’s function without impacting all other parts.
For example anyone who has sprained an ankle before will be aware of how this causes them to limp, increases the energy required to walk, and even changes their upper limb and body posture and movements when attempting to get around. Restoring movement and function to the ankle will tend to resolve the other bodily compensations for this injury.
This is why when treating shoulder problems we will always look at global movements in 3 planes of motion through the body to see how and if other regions are impacting the success of movement in the shoulder complex (e.g. a stiff and tight hip complex). Hence the body is a unit and must be treated as such if the outcome is to be successful and lasting for the individual.