My question refers to training programs that call for multiple sets of, for instance 10-12 reps. Do I need to use the same weight for each set, or increase the weight on each set? I've been doing the beginner blast off program for about 2 weeks now, and that last set is very tough, and I always try to increase the weight for the next workout whenever I can do more than 12 reps with good form.
If the last set becomes difficult, then logic would dictate me to either: decrease the weight (so as not to compromise form), or lessen the reps (same reason). If you want to increase the weight, then you would perform less reps.
Here's what I did for the first six weeks: It's not perfect, but it works.
Upper body: Set of 10 (add weight), set of 8 (add weigh), set of 6 (don't add weight). If I could a last set of 6 - I'd increase weight for next time (if I couldn't do four, I'd lower the weight for the next time).
Lower body is basically the same but we started with sets of 15(12,10,8,8). Why? Cause legs are pretty strong. It worked for me, but I changed routines after a bit.