This morning I deadlifted 130 kilos 1x5 (doin starting strenght) for the first time. The warm up and the first 2 reps of the work set went well, but in the ascending phase of the 3rd rep I felt a sharp pain in my lower back. In that case there's the stupid thing and the smart thing to do, well I did the stupid thing and went on to complete the set. As a result I had to spent most of my day lying in bed because I could hardly walk properly. Now I'm wondering, why did that happen ? I noticed that I have a tendency to arch my upper back when the weight is very heavy for me. Problem is that when this happens I can't feel whether my lower back is arched or not. I've postponed wearing a belt (never wore one as of now), following Rippetoe's advice to not begin wearing one until I stall. Would it be a good time to start wearing one ?