If you haven't exercised in years, it's important to see your doctor before starting any fitness program. Barring any acute health issues, your doctor will probably recommend you begin a well-rounded fitness routine for a healthy heart, strong bones and pain-free joints.
As a beginner, you will want to start slowly to avoid injury to your muscles and joints. While working out will make your body stronger, too much too soon can create soft- tissue injuries like tendonitis and sprains. To avoid injury, choose a lightweight, high-repetition strength-training routine for your legs, hips, shoulders, arms and back. Choose a weight or other form of resistance, such as resistance bands, that you can do 15 reps with good form before taking a break. After at least four to six weeks of consistently using the lighter weights, try upping the weight and lowering the reps.
For your cardio routine, choose a low-impact exercise such as walking, biking, swimming or stair climbing. These activities will help you boost your aerobic capacity and burn calories, and they're easier on your joints until you have the strength to safely do more high-impact training.
Balance, core and flexibility training are important precursors to more challenging activities and should be included in your fitness routine to help strengthen and support your joints. Pilates, yoga, and stability ball training are great choices for this type of training for both the novice and the experienced exerciser.
Keep in mind is how often you plan to exercise. While it is advisable to start slowly by choosing exercises that won't hurt your joints, the number of times you exercise each week needs to be fairly consistent for any positive change to occur within your body. If you have led an inactive lifestyle recently, try to work in at least 20 minutes of exercise each day. If you already lead a fairly active lifestyle—you take the stairs when you can, you often play outdoors with your kids, you are often on your feet and walking—then start by devoting 40 minutes to an hour three times a week to pure physical activity.