The Altus Athletic - Fitness By Cathe Fitness Ball is a safe and fun way to build hand and forearm strength and increase flexibility. It's a weighted ball, with soft vinyl exterior and flexible sand core for comfort, durability and safety. Ideal for yoga, pilates, light resistance or rehab workouts. User-determined handgrip for comfortable and flexible use. Fitness balls have become very popular due to their vast array of exercise possibilities. The Altus Athletic Fitness Ball is the superior choice in this category, and is an essential component to many exercise programs, including aerobics, flexibility and toning, strength rehabilitation and sports-specific training.