Consider the arm most people bring forward when they roll. If you tense up the arm and shoulder than the impact on you will be much greater than if you relax and just hold the arm in the alignment you require to meet and combine with the floor. Not everything is smooth and straight so you have to learn how to roll up a hill, in a furnished room and so on. Try for example rolling on the spot so you don’t advance as you roll. Easy to do if you for example have a leg of a chair to pivot around without placing your mass on it. Again to the roll: Lower your body toward the ground and place your hand on it as you turn the shoulder so your surface is more suitable to meet the ground (less edgy and more soft tissue on hard surface) now slowly at start move forward and remember, this is not a fall. There is no need to bring yourself off balance or jump. Just move the same as you do in a normal step. This applies to diverting a hit to and to anything really. It takes very little movement and power to move an arm off course. If you are tense and leaning on the arm moving than you are getting all energy inside of you. If you just move with a relaxed body relying more on your structure (bones and connective tissue) and relaxation (an even nerve activation or full awareness) than the job is done and no hurt has been done to you and hopefully to anyone else. A coin well placed on the tracks can run a train off. Think about it.