I have heard that sentiment many, many times. While it seems logical, delayed onset muscule soreness (DOMS), or that soreness you feel days after your workout, does not indicate a workout's quality at all. You can be sore from walking 35 miles, but walking 35 miles is not an effective workout (note: unless you're muscles are very weak, walking is unlikely to stimulate positive changes to your muscular, cardiovascular, or skeletal systems).
In short, here is what you need to know about DOMS:
- It is a result of performing an activity you haven't performed before, or at least not in a while. The only clients I have that usually experience soreness are beginners in their first 10 workouts or have just returned from a long absence. If you are continuing to feel soreness after workouts and have been exercising for a while, it is possible that you are switching up the routine too often to measure and experience progress.
- DOMS usually starts around 24 hours after a workout and can last over 72 hours in extreme cases for beginners.
- Stretching does not prevent DOMS from happening. The most effective technique in decreasing soreness that I have witnessed is actually repeating the activity at the intensity that first made you sore. For example, if your gluteus maximus (the largest hip muscle) is sore two days after peforming a set of squats till muscle exhaustion at 135 lbs., then perform a set of squats to exhaustion with 135 pounds again (you can read more about these points in my post about stretching, "Closing Bridges").
- The best precaution you can take to avoiding soreness is to gradually work your way into a routine. Start with only a few exercises at a modest effort and weight, and gradually increase all three with each subsequent workout until you're working till muscular exhaustion on at least eight exercises in less than 90 seconds.