Small addition that makes the numbers concrete, because "it becomes heat" can sound like a technicality rather than a real quantity.
An adult descending one storey releases roughly the energy of a small biscuit. Descend a tall building's worth of stairs and it adds up to a meaningful amount of heat dumped into your legs, which is part of why long descents make you warm even though you are working less hard than on the way up.
Hikers know this from the other direction: the descent is when you take a layer off, not the climb.