Running is a very useful infantry skill. It’s a very necessary part of a military drill we called “Getting out of Dodge.”
For our SAW, the M60, we had the gunner who carried the weapon, an ammo belt, and gloves, the assistant gunner who carried extra barrels, tools to change them, gloves, an M-16, magazines, and ammo belts, and just about half the rest of the guys would carry a belt of ammo for them. You always selected football lineman types for Gunner and Asst Gunner.
I’ve read that nowadays, you want a ground pounder to be able to carry 1/3 to 1/2 of his body weight. A mantra that I learned back then and that still works for me is “You’d be surprised at what you can get used to.”