Your feet carry the weight of your entire body so give them a relaxing treatment using the Gymba Massage Balls. The grey massage ball is slightly softer, and the black massage ball is harder. Start off slowly with the softer ball and increase pressure gradually. The massage balls are removable, so you can place them on the board anywhere you wish. For a more precise massage use one ball, and if you wish to massage a larger area place two balls side-by-side. The best massage effect is obtained when using this feature without shoes on.