Are wheelchairs in fact carbon neutral? Even disregarding carbon during manufacturing/delivery to the point where it is at your door, can you say positively that a user does not burn more calories using a wheelchair versus other alternatives of getting around? Can you say that calories not burned by someone wearing an efficient exoskeleton will never outweigh the energy savings of a wheelchair or alternatives?
To treat your questions seriously, yes a manual wheelchair is carbon neutral.
- Carbon from manufacturing/delivery is comparable to a artisan-made bicycle - approx same manufacturing process, and style and size of business.
- Pushing a wheelchair burns about as many calories as walking. If you think about this it makes sense - you have smaller muscles called upon to do the work, but you're engaging less of your body in the effort, and you have the mechanical advantage of wheel.
Some data's available here, which puts wheelchair in the middle of light exertion walking.
Finally, using a wheelchairs all about sitting on your ass all day - how couldn't it burn less calories!