As the other guy said, if check your inventory screen towards the bottom right there's an indicator of whether you have a "low load, med load, heavy load". Every item you equip including weapons that you can hotswap to add to your carry weight, at 70% and above of your maximum, you will "fat roll" which is incredibly ineffective. Swap to lighter armour until you're med. rolling. Endurance is your key stat as it increases not only your stamina bar but also your max equip load.
Once you're med. rolling, it is by far the most effective way to play but it still takes time for it to "click". You're invincible for the middle frames of the animation so it's about getting used to rolling just before an attack connects.