I've been lifting for two years and I've seen some results, but I want to maximize them. My question is, how important is knowing your 1 rep max as far as judging how much you should be lifting and progressing. I.E. should my base start out as lifting 20% of my 1RM one week and then move up 2% the next week, and so on?
Also, how do you structure that particular workout day, does it count as a workout or not, what exercises/body parts should I do and when should I redo my one rep max to see if I've gotten stronger??
Unless you follow a strength-oriented program, based on percentages of your 1RM, knowing it is not dramatically important... Anyway, if you want to test it, follow the protocol shown in the "How to warm up for a One-Rep max" article. Of course, test only "big lifts" (bench, squat, deadlift...), but, again, it is not necessary.
Knowing your 1RM is just a reference point. A 3 rep PR is just as good as a 1 rep PR.
As far as where you should start, that depends on your goals and your routine. As a general rule, when I switch routines, I'll start with less than what I know I can do. So I'll start with 80-85% of 1RM for 8x3, and increase by 5lbs each week. When I get to a weight that I can't do for all eight sets, I'll drop back 10lbs.
I usually just do that one exercise for that day. It definitely counts as a workout.
You don't have to max out that often. You'll know when you've gotten stronger because your workout log will show it. You do keep a log, right?
It doesn't matter at all. A lot of coaches/trainers dont even use % of 1rm anymore because they vary too much. It kinda depends on the program you are doing, but say you are doing 3 sets of 10. If you use the same weight on all the sets and on the last set you can do more than 10 then you need to raise the weight.
One use for it (not that there aren't others) that has relevance for anyone is that there is such a thing as a weight that is too light for productive training, at least for the most part.
There's no exact cut-off but for example it's reasonable to not go lower than 60% 1RM most of the time, and with sub-50% 1RM almost always being lighter than what really should be used.
Now, one doesn't have to determine an actual 1RM value to be able to make such a judgment. For example, if you have a 5RM, using a value of 125% of that as an estimated 1RM is acceptable for this purpose; or if having a 3RM, a value of 110% of that.
Yes, one could also re-define the lower end of most-useful weights as being 75% of 5RM or 67% at the bottom end, but the more common practice would be to generate the estimated 1RM number and work off of percents of that.
Doing this doesn't count as a real 1RM: if someone wants to know what you can lift, a calculated value is not the answer to that question.