From The Art of Manliness:

“Modern soldiers ruck with packs that can weigh 100 pounds or more. As Jason McCarthy, a former Green Beret and the founder of GORUCK told me in my podcast with him, “rucking is the foundation of all special forces training.”

Thanks to GORUCK — a company that manufactures rucksacks and puts on rucking-centered challenges — rucking has become a popular fitness activity amongst civilians. Their events have introduced thousands of people to the idea of walking around with a heavy backpack while doing hard things like carrying logs and doing push-ups.”

Read more here.