The longer you do a particular exercise, the less your body will respond to it. Eventually, no matter how hard you try, you can't make any further progress with it. If you foolishly persist, you'll likely have a new injury to add to your resume.
Many commercial exercise programs like P90X make sure you never experience adaptive resistance by prescribing maximum variety in their workouts. The problem with excessive variation is that you never do any one exercise enough to become competent with it.
A second issue is that too much exercise variation makes it all but impossible to enforce progressive overload, which is why those TV infomercial programs don't work very well for most people.
The more experienced you are with any given exercise, the faster you'll experience adaptive resistance with it, which means you'll only be able to run it for a short time – perhaps 3-5 weeks – before it grinds to a screeching halt. On the other hand, if an exercise is brand new for you, you'll be able to do it for a significantly longer time before you'll need to sub it out for another exercise.
The 3 Questions
When considering whether or not to give any given exercise a break, ask yourself:
- Am I still making progress on this exercise?
- Is this exercise still comfortable and pain-free?
- Does this exercise still directly correspond to my current training status and goals?
If you answered yes to these questions, suck it up and stay the course. But if you answered no, it's time for a change.