I've heard of this idea before, but it popped up on the radar again, it's a "common military exercise" since ancient times, and a good form of exercise for lots of people: https://infogalactic.com/info/Loaded_march
Walking is thought to be a good cardio exercise for just about anybody; all this does it add a backpack with some weight to the equation, which turns it in to a lifting exercise and increases the amount of exercise you get per step versus walking with no backpack.
Any thoughts on rucking, or backpacking, or such related exercises?