Article continues below advertisementHailey Bieber has been working on her fitness.Almost exactly one year after the birth of her son, Jack, the model looked toned as ever during a workout.On Wednesday, August 20, Hailey stretched out on a table and flaunted her slim tummy at the exclusive Alo gym in Los Angeles, Calif.Article continues below advertisementSource: @laurenperez/InstagramHailey Bieber stopped for a selfie mid-workout.The mom stunned in a tiny black crop top and leggings, with her brand-new yellow Rhode lipstick case positioned beside her.