Stay balls can increase the effectiveness and difficulty of any core exercise.
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Like your standard stability ball, the stay ball offers an unstable, balance-challenging surface for exercises that would otherwise be done sitting or lying down. However, as the name implies, stay balls don't roll around as much as standard stability balls. This makes them a more manageable tool for strengthening and defining the core muscles, especially for beginning exercisers, as they can worry less about the ball rolling out from under them and concentrate more on doing the exercise properly.
Many core exercises can be adapted to use stay balls. Two popular exercises that beginners use when starting a stay ball core routine are the crunch and oblique crunch, which work the rectus abdominis and obliques. The instability will increase the intensity of these exercises, while the pliable surface of the ball supports your lower back as you move. To strengthen the erector spinae of your back, do back extensions by facing down with the ball beneath your hips and lifting your torso. You can also use stay balls as light weights for exercises like seated Russian twists that work the entire core.
Advanced stay ball exercises can really challenge the muscles of the entire body as well as the rectus abdominis, obliques and erector spinae. For instance, ball exchanges, in which you pass the stay ball back and forth between your hands and feet, engage the hip adductors along with the abs. An extremely difficult full-body and core exercise is the plank pike-up, in which you start with a straight-armed plank with your knees on the ball and your arms holding you off the ground, then roll the ball forward, lifting your hips until your torso is almost vertical.
Sample Stay Ball Routine
Adding a few stay ball exercises to your normal core routine can make your workout both more exciting and effective. A good workout begins with a light full-body warm-up followed by a series of stay ball exercises made up of: crunches, windshield wipers -- holding the ball between your extended legs -- reverse crunches, back extensions, plank twists, Russian twists, ball exchanges and ball roll-outs. Finish with an easy five to 10-minute cool-down. Do this circuit for one to three rounds, performing each exercise for 30 to 60 seconds or 10 to 20 repetitions.
Tips for Sizing
Stay balls come in a variety of sizes ranging from 45 to 85 centimeters in diameter, or about 17 to 33 inches. Different stay ball sizes are designed to accommodate people of various sizes and weights. Most brands and gyms will offer 55 to 75 centimeter stay balls that accommodate individuals from five to six-and-a-half feet tall who weigh up to 250 pounds. The proper sized ball is one on which your knees are bent at 90 degrees when you sit on it with your feet flat on the floor and about hip-width apart.