Maybe the word "obviously" should be "most likely".
I understand there is great interest in having work sessions during the off season. The Colorado Springs Team has been active all seasons of the year, every other weekend, for many years. The Antonito CRF allows projects to continue year round, if somebody can just get the ball rolling. Occasionally there are other special activities on the railroad at other times.
Historically, the Friends have always tried to accommodate those with handicaps. There have been volunteers who have been paraplegic; the Site Helper positions are available for those who cannot perform the strenuous work.
There are other ways to help these types of organization such as committee work, publications, the Library/Collection work, and project planning. I would imagine that if a person became very knowledgeable of it's values and on how the organization worked through these activities then they would be a good candidate too.