"Control" in general is not particularly well defined as a yes/no proposition. You can likely rigorously define an agent's control of a resource by finding the expected states of that resource, given various decisions made by the agent.

That kind of definition works for measuring how much control you have over your own body - given that you decide to raise your hand, how likely are you to raise your hand, compared to deciding not to raise your hand. Invalids and inmates have much less control of their body, which is pretty much what you'd expect out of a reasonable definition of control over resources.

This is still a very hand-wavy definition, but I hope it helps.