re: Who were the most physically fit presidents?

Lincoln.

Derisively called "rail splitter" because he split railroad ties [for fences] as a youth, Lincoln was uncommonly strong ... [Once, a]s the presidential party lounged on the deck, Lincoln playfully demonstrated that in "muscular power he was one in a thousand," possessing "the strength of a giant." He picked up an ax and "held it at arm's length at the extremity of the [handle] with his thumb and forefinger, continuing to hold it there for a number of minutes. The most powerful sailors on board tried in vain to imitate him."