From RECOIL OFFGRID:

“Ruck marching is the latest trend in the world of “survival athletics.” It’s inspired by the tradition of military marches, where soldiers carry heavy packs to build endurance. When proper precautions are taken, “rucking” is a safe and highly-effective exercise for burning calories and building functional strength. More importantly to survivalists, it’s a great way of testing yourself for any future bug-out scenarios.“

Read more here.