The ADA prohibits asking directly about disabilities or anything else that's not directly related to the job. However, it is legal to ask questions that might reveal a disability, as long as it relates to the job.
For example, if I'm hiring for warehouse stocking, I could ask if you're capable of lifting a 20-pound box, if the job involves that. I couldn't ask, though, if you have any physical disabilities, or ask somebody who wouldn't be required to lift boxes fairly regularly.
If the person I'm hiring might have to lift one box maybe once or twice a month, but it's not a significant proportion of their job responsibilities, then if they had a disability, letting them ask somebody else to do it or providing some mechanical means would be considered a reasonable accommodation.