I saw this guy on the lakefront here in Chicago late last week:
In case you can't tell, those are two tires he's dragging, tethered to his waist, across an snowy/icy dirt path along the lakefront. I wasn't close enough to see if there was anything inside the tires.
He wasn't running, he was power-walking with trekking poles. I'm not even completely sure what he was training for, though I assume it was a workout for the lower body power muscles. (Maybe it was a final training session for this race, which just started yesterday.) He covered at least 4 or 5 miles like that, because I saw him headed back in the other direction 40 minutes later.
I wonder what happened when he passed the dog play park a mile down the path?