You could risk injury any time you touch the bar, or do anything. I do a full bodyweight warm-up (pull-ups, push-ups, squats, stuff like that) before I even touch a bar so the joints are warmed, which is literally all a warm-up does. The warm-up lifts are just to prime the CNS for a heavy load, but there really is no way to adequately prepare for a 1RM. And if you are fatigued, you mess up any chance of making the 1RM, which is literally the only lift that is important for that day.
Note the last 4-5 lines of that page. If you don't want to do it the way I do it, that's fine. I have reasonable confidence in my technique and methods, and like to be done inside 30mins in the gym because I'm lazy. But 7 warm-up sets at those volumes is waaaaay too much. At least cut it back to 3 sets of no more than 3-5, at like 60%, 80%, 90%. (I would go 5x, 1x, 1x at those %s myself but whatever you think best.) Just write down your results and change it up if it doesn't work.
Alternatively, look for some other explanation. Tired? Hungry? Injured? Technique slipping?
