My wife had me buy her a treadmill last year. It wasn't too bad when
it was in the main part of the house. But it was moved to a guest
bedroom that was usually left closed up.
When you opened that door, it was like you opened a gym locker that
was left for a whole year closed up and rotting.
Everything in the closet in that room (mostly our winter coats, etc.)
smelled just old sneakers.
We tried washing in this and washing in that, even used 1/2 a gallon
of OdorBan from Sam's in the things that could be washed, sprayed
those that couldn't be washed with the Odor Ban using it like Fabreze,
but nothing helped.
A cousin stopped by and went out to his car and came back in with that
Knight & Hale Body wash and washed down the treadmill belt, and then
told us to buy some of the spray for our coats.
It removed all of the smell from the clothes quite well, but the belt
still has a slight odor but not enough to permeate the room like it
did. A little plastic clip on fan blows across the belt now too and
in only a few weeks, you don't notice the odor much anymore and it's
still in a closed room.
FWIW: My brother is in the used car business. They slip a sliver of
these treadmill belts up under the passenger seat and a couple of
slivers under the rear seat, up in the springs.
Makes the car smell like a new car for a long long time.
Me, I think it makes them smell like dirty sneakers!