It takes five weeks of consistent repetition for tasks like working out to become routine. With that in mind, it is important that you shape your workout schedule in a way that you know you will stick with for at least that long. If you hate running, don't schedule a 5-mile run on the treadmill every other day. If you're a beginner, start off slow to avoid burnout. The more you ease into an exercise routine, the less likely you are to be extremely sore the next day and the easier it will be to stick with your routine.c 

If the exercises you incorporate into your workouts aren't fun, exciting things that you look forward to, you'll get bored and won't stick with it. Variety will help you look forward to your routine and not dread exercise. Get ideas from fitness magazines or try a new fitness class at your gym.

The other reason variety is important is that if you perform the same exercises over and over, your body will adapt to the way you're working it and stop improving. Changing your workout every four weeks will prevent you from plateauing. You can change the amount of weight you use, the exercises you perform or the type of cardio you do, but be aware that the more you exercise, the harder you will have to push yourself with each subsequent workout.c