If you have a couple spare minutes, check out the embedded propaganda video about U.S. Army Air Assault School.
Here's why this school is so hardcore: one of the requirements is a 12.0-mile ruck with a 50-lb. pack in under 3 hours. That may not sound that hard, because going 12 miles in three hours is *only* a 15-minute per mile pace.
Until you try it, that is.
At that type of pace with that type of pack, the ruck becomes something of a walk-run hybrid.
I recently read that the most frequently-made types of New Year's Resolutions involve personal health -- physical fitness and weight loss. To anyone looking for a phenomenal combination leg/core/cardiovascular challenge, resolving to go 4 miles in under an hour might be a good vow for the New Year.