Twenty minutes is considered a minimum time for the exercises to be effective. Exercising beyond 30 minutes probably provides no additional benefit. After exercising, there should be a cooling clown period for muscles and heart rate to return to their pre exercise state. An exercise routine with the more stressful ones in the middle helps achieve this goal. Exercises should stress control, rhythm, stabilization of the pelvis, and proper alignment of the pelvis in a posterior-tilt position.
Swimming provides rhythm, controlled breathing, and water buoyancy.
Drink plenty of fluids before and after you exercise. Do not indulge in rapid exercises with uncontrolled momentum. Sudden or exaggerated motions will severely stress ligaments and joints that are already relaxed under hormonal influence. Don't exercise outdoors in hot, humid weather. Don't bend deeply or greatly extend your joints and don't stand up abruptly.