Aha but who said in RWR they were carrying so much equipment? The character models seem to only have a few pockets and things for small stuff, and a gun (with unlimited ammo

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So it seems to me that 30 pounds of M240 + maybe 10 pounds of pockets stuff = a very dive-able character

Anyways, even if I were carrying 100 pounds of equipment, the rigorous training it takes to become a soldier (assuming these two teams had formal training) and the adrenaline rushing through your body, combined with knowing that if you don't book ass now, you will die, may just be enough to let you dive out of the way of a grenade. Now I never envisioned diving halfway across the map but far enough that if you were on the edge of the grenade kill-zone, you can make it out or if you were a little out of cover, you could make it back with a high probability of survival. As someone above said, getting up could take a while to balance the maneuver and also for your character to get his breath back.
ComJak