There is an old saying, "If you do what you've always done, you'll get what you've always gotten." That motto applies to all facets of our lives, but especially to our diets and our exercise routines.
If you continue to eat high-calorie, low-nutrient foods, you'll continue to resemble the round muffins and squishy bowls of noodles that are entering your body. And if you do the same exercises week after week, your body will stop responding and remain stuck in neutral until you rev it up again by moving it a new way.
This phenomenon is evident at every gym in the world. If you spend much time at a fitness center, you'll see plenty of women who look exactly the same week after week. That's because they have found an exercise routine they enjoy and have been faithfully doing it ever since. Yet they wonder why they still can't lose that jiggly underarm fat or why they've performed 10,000 crunches over the last few years but still can't see their abs. It's because their bodies adapted to the old routine, so those same moves aren't effective anymore.
Another reason to alter your workouts every few weeks is to avoid boredom. Once your exercise time becomes ho-hum, you're more likely to find excuses to avoid it. One day your excuse will be that you don't feel well. The next day you'll have too many things to do. Then a doctor's appointment, house cleaning, and a sick child will become the excuses du jour until before you know it, it's been a week since you've exercised and suddenly you've become sedentary.
Avoid falling into an exercise rut by trying something new this week. It can be a little intimidating to take up a new sport, try a new class, or attempt a new set of strength exercises from a DVD or book. You may wind up doing some exercises you don't enjoy, but you'll probably find a few that you didn't know you liked, because you've never tried them before. (Zumba, anyone?) It's up to you to take the initiative and exercise outside of your comfort zone. If you want to see change, you gotta make a change!