Need not be anything strenuous. Just a dozen pushups are good enough and take hardly half a minute. Jumping up and down like a little kid is fine too! The idea is to divert the mind away from the source of stress.
Right, but when it is exhaustion from not sleeping for days at a time and working 14+ hours days 7 days a week for weeks at a time it stops being about stress and simply trying to stay physically and mentally conscious. It sounded to me original question was about dealing more with exhaustion than stress. For stress, I would consider exercise an excellent suggestion.