Those treadmills are heavy as fuck. Probably just easier to load the firewood by hand.
My ex gf bought one off FB marketplace about 10 years ago and I had to go get it outta someone's basement. The stairs were about 6 steps up, a 90° turn, then another 20 steps up to the top. The dude selling it had one end and I had the other.
Got it in the back of the pick-up, paid the man, and went back to her place.
When I got there she'd called her cousin to help me move it into her house.
He looked at it in the back of the pick-up, looked at her, and said "
Wait. Didn't you just sell one of these a couple years ago?" She answered "yes" like it was no big deal.
Of course getting it into her house was two more sets of steps, but only about 6 each.
I can't imagine dragging a treadmill around whenever I need a load of firewood.