Protip: Sprint your full stamina bar, then turn around and look at how far you went. It can't be more than 100m, which any reasonably fit person could cover no sweat. Remember that gear disperses well across your body, and even carrying ammunition, canteens, and backpacks, you could reasonably sprint ~100m. I've done it several times in weekend-long airsoft games where I had to carry a dozen magazines, water, and food supplies with me. I was perfectly capable of running at near-top speed through rough terrain (thick underbrush, up and down light slopes, etc.) for 50-100m bursts, and I'm not in the greatest shape.
Again, RO2 has been retooled to be a lot more realistic than RO1. Everything is represented in realistic distances, and weapons and soldiers behave like their real life counterparts. This will take some getting used to for those of use used to RO1s sluggish plodding, but it is FAR more realistic now than just about anything else on the market.