To train core, legs and upper body it helps to be on the ball

The laws of physics say there will be an equal and opposite reaction in such an event.

That’s where it gets funny. Someone always goes flying backward or crashing into something.

Stability balls are good for other things besides breaking furniture and causing whiplash. You can get a pretty good workout if you use them correctly.

I use the stability ball, also called the Swiss ball or balance ball, to help my clients not only train the core but also the legs and upper body. What you work depends on how you use it.

To call something a “stability ball” seems like an oxymoron. How can you have a ball that’s stable?

You become the stabilizing force when exercising with the stability ball. The ball creates an environment of controlled instability in which you perform. As you master easy exercises, you can progress to harder ones.

That’s where the exercises in today’s column apply. They are more on the unstable side of the spectrum.

If you have mastered the stability ball crunches and the plank, then the hamstring curl and the toe crunches should be simple to learn.

You should start by choosing the correct ball. I try to find one that is about knee height. Having a stability ball that is too big or too small will lead to awkward positioning and frustration.

Have a trainer or gym buddy close by to watch your form. Hip position is important with today’s exercises. If the hips sag, then you’re not doing them right. The hips tend to be sneaky. You may start with the core tight and glutes contracted but they will undoubtedly sink if you’re not concentrating.

If you find the exercises today are a bit challenging, you can easily regress them by holding the starting position for 60 seconds. When you feel comfortable, add the action. Ask a trainer or gym buddy to spot your wobbles and keep an eye on your hip position.

I like to use the hamstring curl because it is easy on the knees and requires substantial effort from the core. Toe curls may take a little more practice to master but the rewards are sweet. If ether exercise becomes too easy, progress either of them to a single leg exercise instead of a double leg exercise

Chris Huth is a Las Vegas trainer. You can contact him at 702trainer@gmail.com. Before beginning any exercise program, consult your physician.