The heavy ball supplies the resistance as Gilad takes you through all the core muscle groups. Lots of core workouts neglect the mid and upper back muscles--but not this one!
Core Challenge is beautifully designed to work both the entire abdominal region and the opposing back muscles, to help you develop a stronger, balanced midsection.
NOTE: A 3- to 5-lb. dumbbell can be used instead of a heavy ball
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