Bob,
I do carry both of my D700's at the same time. On one of the bodies I'll have the 70-200mm and on the other body I'll have either my Tamron 28-75mm or the Nikon 17-35mm. But, as I've gotten older, I've gotten wiser, I'll bring along either a tripod or monopod for the D700 combo with the 70-200mm lens because like you, as the day wears on, that equipment gets quite heavy.
By the way, I do work out, but more cardio instead of strength training.

Cheryl