Here's an answer from Nick on Facebook, 'I suggest starting with Hill climbers, When you get a swiss ball, put your hands on either side and bring your legs back in an almost push up like position and raise your knees to the ball. Skydivers (lie on your front with legs and chest raised and hold it) A plank super set (so hold one side then swtich to another when u run out of energy) and reverse crunches. Maybe a lil more than 20 mins or around it.'