We can all agree that progressive resistance and high intensity training are the key to seeing serious strength and size gains. But warming up properly is equally important, and in fact, warming up is an integral part of HIT--too few warm-up sets and you could miss out on strength and power during your working set, too many and you'll end up in the same boat. Here's my guide to a great warm-up (and a great workout).
Depending on your joints and fitness level, more or less warming up may be necessary to function optimally during training. For someone with no injuries or problem areas, a fairly simple warm-up can be implemented before starting in on your first exercise. For individuals with some sore spots or other problems, a more extensive and specific program can be used. I like to start with a very simple but thorough warm-up, one for lower body and one for upper (regardless of target muscle groups). For upper body, I like to do one set of each of the following, each with ultra-light weight and in this order: side laterals, front raises, rear delt flyes, dumbbell curls, triceps pushdowns, and cable lat pullovers. For lower body, leg extensions, hip adduction/abduction, and leg curls are on the menu. Now even though these are being done with very light weight, I still like to approach failure--approach, not reach! This means I'm starting to get some blood into the muscle, I'm feeling the muscle contract and stretch, but I'm not getting fully pumped quite just yet. For someone with pain in any type of movement, a more extensive warm-up will be necessary. I recommend simply performing a few more ultra-light sets of the exercises described above, in addition to some joint-specific exercises. For shoulder stiffness or discomfort, try adding some very light rotator cuff exercises and stretches; for knees and hips, try adding some stability exercises, such as side-to-side and front-to-back heel slides, as well as a few minutes of cardiovascular exercise to the beginning of your workout.
After my little "upper or lower hemisphere" warm-up, I start in on my first exercise. I've touted HIT and one working set for years, but that doesn't mean I don't do multiple warm-up sets on each exercise. For my first exercise for a target muscle group, I may perform as many as 4 or 5 warm-up sets, and up to 2 for each additional movement. I like to keep my progression fairly even, meaning I like to increase my weight by the same poundage after each set--individuals who are moving significantly more iron may want to think about percentage-based increases rather than going strictly by the numbers (because a 10 lb increase on a 200 lb lift doesn't make a whole lot of sense).
In addition to increasing the weight each set, I also reduce the number of repetitions performed. Early in the warm-up I'll do as many as 10 or 12 reps, but as I approach my working set, I taper off significantly. My rule of thumb, especially when I may be trying to reach a new working weight, is to stop after 6 reps in the warm-up set(s) immediately preceding my working set--if I can do that many reps without feeling like failure is only a few more reps away, it's time to slap more weight on there and go again in a minute or two. It's tempting to keep going, because that pump feels sooo good, but trust me, you don't want to miss out on even just one rep later.
Set timing plays a role here as well. Trying to perform a working set too soon after your last warm-up set is just as detrimental as overdoing it during the set in question. Yes, warm-up sets prime the muscle, but it is still necessary to allow for some waste removal and re-oxygenation prior to lifting again. Your body will tell you when it's ready again--all you have to is listen! And then lift the weight of course.. But that's the easy part, right?