Some system stress is required to function: Mitochondria, our cellular energy and power factories are always producing Free Radicals at a low level, but weak and damaged ones don’t get weeded out, so background free radicals are higher.
Motion speeds up the process of free radical production, which leads to more sparks from the energy “burn”, which then kills and culls out weak Mitochondria and therefore reduces background free radicals. So motion keeps things cleaned up and thus increases energy efficiency.