When an individual has worked hard, kept the comittment and seen the 'fruits' of their labor, it's difficult to get them to change the routine that has gotten them the results, reached the goals and acheived the body they wanted. However, if you do not CHANGE your routine in some subtle ways, the progress and the changes will stop!
The body is an amazingly effecient machine... It hates stress, whether it be mental (stress at work, under a deadline, home alone with the kids, ect...) or physical (working out, resistance training). Your body will strive to find the path of least resistance when under stress. This is called Homeostasis.
Whenever you begin to exercise or start a new routine, the body will not know what muscles to activate in order to overcome the movement. For example, lets say you begin step aerobics and in the first month you lose 10lbs. What is happening is the body is activating your muscles in order to overcome the stress your putting it through. In month 2, your body is beginning to learn what muscles it needs the most and the ones that it may not need to work as hard. By month 3, the body has become efficient at identifying exaclty what muscles should be stimulated and what muscles do not need to be stimulated. This reduces the amount of stress your body is under, but the less muscle you stimulate the less calories your burning thus the less weight you lose.
There are a few set of rules that one should follow in order to keep their routine interesting and effective. These are fail-safe, effective rules that I ALWAYS teach my clients to empower them. You can take these rules to any gym across the world and feel competent and confident in your routine.
Rule #1: FITT Principle
Frequency - How often your working the muscle group. (Days/week)
Intensity - How many reps are you doing. (8-12, 12-20, 20+, 4-8 optional)
Time - The amount of time taken in between sets. (30 secs., 60 secs., 120 secs.)
Type - What type of exercises are your doing.
Follow these rules to maximize your time in the gym. I always tell my clients to make sure your getting "100 pennies on the dollar" when it comes to your time in the gym and this principle is one way to make sure your making every minute inside the gym... COUNT!!