A strong core is important for preventing aches and pains. You can improve your core in just 7 days with this plank routine: on day one, time yourself performing a plank for as long as possible. Each day, for seven days, add an addition ten seconds to this time and plank twice a day. In a week you will have added a minute to your time! Remember, you can lessen the intensity by performing the plank on your knees- just make sure to keep your back straight as you focus on pulling your belly button in toward your spine.