I feel the need to mention that I found early on arm fatigue is usualy a sign of need for a taller, or shorter bench. I started with a desk. After while my shoulder would get stiff, and then sore. A friend I mentioned it to suggested a taller bench, and helped me measure the proper height for me. It made a world of difference. I was able to go without the shoulder pain. (My shoulder has been through a rough life as has the rest of me. You could publish a manual on trauma care from a couple of years of my life.)
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.