The reebok womens training 55cm gym ball is a slightly smaller exercise ball made for users between 155cm and 167cm 61 x 657 tall working out with a gym ball allows you to perform a number of quality exercises to target your core and improve posture flexibility and your general fitness examples of possible exercises include tricep dips crunches the plank shoulder curls and press and side squats and there is a workout dvd included to help you on your way as well as a pump the swi