Take control and meet your fitness goals without expensive exercise equipment. Using a stability ball will improve the strength of your abs and lower back. Since a Yoga ball is unstable, you have to use your body& 39;s core strength to remain balanced, which in turn improves proprioception, flexibility and body alignment. Feature - Color: Random. - Material: PVC. - Size: About 55 x 55 x 55cm. - Enjoy Outdoor Fitness Sessions: Take the yoga ball outdoors, exercise in the fresh air, and let nature be your coach. - Train in the Comfort of Home: Train, stretch, and take care of your body without even leaving the house. - Keep Fit at Work: Experience a new way to stimulate your muscles by simply sitting in the office. - Exercise balls are perfect to increase balance, strength and flexibility. - With this versatile piece of fitness equipment you can get trim and toned by exercising abs, back, hips, etc. making it the full-body tool.