Strengthen your core muscles in just seven minutes with this quick yet effective ab workout shared by NASM-certified fitness trainer Allie Gibbs. It involves seven different ab moves that are mostly bodyweight, except for three moves that require a mini resistance band. This is the perfect workout to tack on to a cardio or HIIT workout, or if you don't feel like doing a full workout but want to get in a little movement. Do one minute of each of these seven moves for one round.