Recently a very dear friend and former client asked me some questions about how to change up his workouts so that they'll keep him challenged over the long run. Should he increase his reps? Keep trying to add weight? Juggle dumbbells while eating a ham sandwich?
The obvious answer would be that it's time for a new routine, knowing that he's kept to the same one---in various incarnations---for a few months now. Most of us know when we need to mix things up. But he brings up a valuable question, one I suspect many regular exercisers have pondered: What do you do after that? How are you supposed to make this stuff work for you in the long run?
It's true that you should alter one or more variables in your routine every 6-8 weeks or so. This can mean changing the number of sets and reps, changing the order of your exercises, or choosing new exercises all together. Whatever changes you make should introduce new challenges: the lunges you've been doing should start hurting all over again (but this will subside as you adapt to your new routine).
This doesn't mean, however, that you'll constantly have to overhaul your workout. You might only have a couple of routines that you're familiar with. This is okay---you just need to get familiar with the practice known to fitness experts as periodization.
Traditionally, this was a practice developed for training athletes and bodybuilders, and it involved cycling periods of working out using heavier weights/lower reps with periods of lighter lifting and increased repetitions. The point was to avoid overtraining, or getting to the point where the lifter's body became exhausted by lack of change in the workout.
But periodization can also be be applied to any resistance-training regimen, whether your goals are to get huge or just tone up a bit. Here's an example of what I recommended to my client (who I should mention is fairly well adapted to strength training): alternate a period (the length will depend on how long it takes you to get out of the "alarm phase" of training to the point where you're no longer experiencing soreness from a specific routine) of doing the machine-based, more isolated exercises he's accustomed to with a period of more dynamic, bodyweight-focused exercises. This will ensure that over time he trains a variety of muscle groups and fiber types.
After he's switched it up for a while, he's then free to go back to his machine-based routine, provided that he experiment with variations on the exercises he knows so well. You can do the same: If you have two familiar routines you can alternate between, consider consulting a trainer for ways to shake these up over time. He or she might show you a new way of doing a familiar move, or how to do the same exercise with a different piece of equipment, or how to reorder your routine so it feels fresh. It's not an overhaul---think of it as a reinvention.