It can be hard to be motivated to work out if your knees are achy or your back hurts. If you're in that boat, swimming is an ideal exercise. It's easy on your joints, you’ll use both your upper and lower body, and you'll get a good cardio workout. You’ll reap the benefits from the resistance of the water, too. If you swim for a half-hour a few times a week, you’ll lower your risk of heart disease, stroke, type 2 diabetes, and some cancers. It'll also bring down your bad cholesterol and blood pressure.