For any well-rounded fitness program, there are three key elements that should be covered in every workout:

• Strength
• Cardio
• Flexibility

There are countless possibilities in how you approach this mix, depending on your needs, limitations and preferences.

Here are just a few examples of needs and preferences: muscle mass, muscle tone, weight management, improved posture, improved endurance, improved joint mobility, improved core strength. You might have aesthetic needs: a great beach body, a set of six-pack abs, a great set of pecs, or just an overall lean look.

Once you have covered those three bases, there is a lot to be said for mixing things up from time to time. The word “plateau” gets used a lot in this context; you progress to a certain point and then stay there. Once you have done a fitness routine for while and seen positive results, it’s easy to do the same thing over and over; after all, you’re getting good at it…why change?

I’ll explain by way of example. Recently, after about six months of doing body weight exercises, I decided to do a couple of sets of dead lifts and squats. I didn’t pile on the weights–I stayed within my safety zone. The next day, my entire lower body was sore. It felt as if I hadn’t set foot in gym for five years. Muscle conditioning is part of the process of adaptation–you break down tissue and allow it rejuvenate. Adaptation can happen on a very subtle level; stop doing the bench press for a few months, replace it with push-ups, then try going back to the bench press and see what happens.

When making a customized program, a top personal trainer should maintain a balance of repetition and change. Doing the same exercises again and again leads to a plateau and leveling off effect. At the same time, throwing a bewildering array of exercises at your client creates confusion. There should be enough predictability to see progress, and enough change to prevent plateauing (not to mention boredom).

Here are a few ideas:

• Change the equipment (e.g., medicine ball instead of dumbbells)
• Change the surface (e.g., push-up on a stability ball instead of the floor)
• Change the distribution (higher weights and fewer reps)

This balance of repetition and change is something I now strive for in my own workouts and the workouts with my clients.