Obligatory drive-by treadmill post
This page shows some photos of a harness meant to pull a pulk sled. A pulk is a runnerless sled used to haul supplies for winter camping or expeditions or, closer to home, a small child or a pet who can’t ski or walk through the snow on a daytrip or on the way to a winter cabin.
Seems to me the basic idea would work for manhauling with a cart, too.
edited to add: Pulk adapted for carrying a kidlet.
Yes, But since the events are timed, I they don’t seem to be having that many injuries I would assume that the harnesses are designed to allow maximum force applied without injury.