In each Outbreak Mission you’ll be chased from behind by an enemy horde (like zombies, aliens, robots and more). If you fall behind, you risk being captured or assimilated. You stay ahead of the horde and progress toward your distance target using your steps.
Along the way, you’ll run into obstacles that block your path. Obstacles range from everyday packs of enemies to creatures, monsters, barricades, and boss villains. You use your exercise to battle/conquer obstacles, as well as heal yourself and/or your teammates when you take health damage.
In game, you get some exercise points just for walking, but you can make overcoming obstacles much easier by tracking non-walking exercise.