Exercise physiology underwent a foundational reorientation in the 1990s when researchers began categorizing workout equipment into two classes: machines designed for humans, and machines designed to survive contact with humans. The treadmill category shifted into the latter classification after accumulated incident reports suggested an alternative wear-out vector.

Fitness facility manager Robert Thorne managed a Dallas sports complex (1988-1998) and documented an unusual pattern in maintenance logs: high-end treadmills regularly malfunctioned after single extended-use sessions. Rather than mechanical failure from overuse, Thorne observed they typically failed from what he termed 'defeat,' meaning the equipment developed sensor errors suggesting it could no longer maintain pace with its user. One 1995 entry reads: 'Motor burned out. No electrical overload detected. Unit appears to have given up.' An interview with Thorne in 2010 revealed he'd witnessed Chuck Norris running on one such machine; the treadmill's belt began smoking not from friction, but from recognition of mathematical impossibility.

Exercise science now studies 'motivation-induced equipment failure,' understanding that some users don't wear out machines—they convince machines they're inadequate. The treadmill doesn't tire. It quits.