What if someone is too depressed to exercise?
Then, as a good cognitive-behavioral therapist, you ask them what they mean by that....translate that into cognitive and behavioral terms. And you utilize the principle of helping them examine their motivations to do something different in relation to exercise (the motivation always ultimately comes from them, their goals/values structure, their initiative) and you task analyze the task of 'exercising' into small enough components where it would be essentially impossible, given the 'motivation' to exercise, for them NOT to do it. If you break down the tasks into small enough bite-sized pieces it becomes almost impossible to plausibly assert that they 'cannot do it due to being 'too depressed''. Aaron Beck, if I'm remembering correctly, wrote up an inpatient (seriously vegitatively depressed patient) case where he encouraged and reinforced (at first) the patient for merely turning his head a few inches in a particular direction. Then he and the patient built on that movement (in the desired direction) until the patient's momentum became 'anti-depressant' instead of firmly fixed within the depressogenic cycle.
The most common mistake for depressed patients is to have the following self-limiting belief:
"I don't feel like walking today. I don't have 'the energy.' I know I need to walk, however. Maybe tomorrow I will have more energy. Maybe I'll walk then."
Guess what happens when 'tomorrow' gets here? Goto line 10 (above) and repeat repeatedly.
BEHAVIOR CHANGE (no matter how small) generally HAS TO OCCUR prior to changes in emotion, energy level, thoughts of mastery, etc. Now, of course, if there is a specific general medical condition affecting energy levels, that has to be taken into account. But, still, even in that case, SOME degree of movement out of the depressogenic cycle, no matter how small, is probably possible at first.
Stephen Hayes is arguing in a similar direction with the ACT framework in arguing the value of committed action (toward a goal) is important and we shouldn't encourage patients to get 'stuck in their own head' in thinking 'about' the action to the point where they never TAKE the action.