Yoga, weight lifting, and less active sports like baseball are good for you but will not really contribute to cardiovascular health. If you are trying to maintain bone density, choose a weight-bearing form of exercise, such as running or walking, rather than swimming or bicycling. If you are recovering from an injury or have a chronic disease, check with your doctor before you begin. It might be best to start gradually. Ideally, you should engage in some form of moderate to vigorous exercise every day for 30 minutes, but the greatest difference in health is seen between people who don't exercise at all and those who exercise just a little bit.
Injuries can result from overexercise or exercising without warming up first.
Daily vigorous exercise may also cause some women to stop menstruating. If this happens, or if you experience unusual fluctuations in your cycle, do not ignore it. Menstrual changes indicate a hormone imbalance that can lead to other health problems, such as loss of bone density. Consult your doctor. Often, I start an exercise program, but I don't keep up with it.