Strengthening ME sufferers

I've been seeing a few ME sufferers recently and we talk a lot about graded exercise. Not doing too much and not doing too little, but having to strike that balance to get progressively better.

I was wondering whether imagining doing physical exercise in trance in order to build them up would tire them out. Would it have any effect on them or would it only help?

Imaginary exercise - would it wipe them out for a few days?

Andy.