To get started, try this three-exercise progression. Once you've mastered a variation, try the next level up. As you experiment with these moves, you will feel your weight shift from side to side on your foot, which means the muscles that support your arch and ankle are working. If you find your feet cramping, spread your toes wide always exercise in just socks or barefoot.
Standing single-leg biceps curl: Taking this basic arm exercise and creating the double instability of standing on a soft surface and on one leg transforms the move into a full-body exercise. Begin standing on the foam cushion holding five- to 10-pound dumbbells with your arms by your side. Lift your right leg up so your hip and knee are at 90-degree angles. Hold the leg and torso still while you bend your elbows, bringing the weights to your shoulders doing a classic biceps curl. Slowly lower the weights. Do six reps on each leg for three sets.
Single-leg deadlift: Stand on the balance pad and lift your right knee up until it's even with your hip. Keeping your back neutral, hinge forward at the hip, bringing your right leg behind you. Reach your right hand toward your left foot making a long line with with your body from your head to your right knee. Your torso should be parallel to the floor. Return to standing bringing the right knee forward, without touching the foot to the floor. The first few reps will most likely feel awkward, but hang in there, it gets easier. Do 10 reps on each leg for three sets.
Single-leg deadlift with overhead press: To increase the difficulty of the above exercise, increase the range of motion and add some weight to move and hold a five- to 10-pound dumbbell. After completing a deadlift, do a biceps curl into an overhead press. As you bend forward, reach the weight to your standing foot, and once standing, press the weight overhead. Do 10 reps on each leg for three sets.
If you're not sure if your gym has a foam pad, there's probably one stashed with the BOSUs and foam rollers. If not, try standing on a soft exercise mat. It will surely provide enough instability to challenge you.