You’ll need a decent aerobic base, which means you’re okay running and walking for at least three hours. While you don’t have to run 21K in training, regular long runs are a must. Bodyweight exercises like pull-ups and pushups, and weighted functional training, will prepare your body for the onslaught. Test your nutrition and hydration strategy during training runs.
The Beast is off-road, so you’ll need gear to get you through dirt, water, and mud. Wear a sturdy pair of trail running shoes with good grip. If you’re racing in the cold, you might consider layers or compression for warmth. You’ll have access to regular hydration points at aid stations, but many will carry a pack, vest or belt with fluids and a nutrition stash.