On the stepped thread side one of the threadings should be reversed threading. And I'm in agreement that the fixed side was probably for off season training and conditioning.

And if you wanted to get really creative (if not goofy) you could rig up a chain driven generator for the left side while running the freewheel on the right side. Call it an alternative to a dyno hub. Last time I priced a decent dyno hub it was way out of my budget.