BMI, or body mass index, is a calculation based on your height and weight and is commonly used as a statistical measurement of obesity. Generally, a lower BMI means you have less excess weight and presumably less fat. Working out to reduce BMI should consist of cardiovascular exercise and weight lifting, but avoid building too much muscle mass because muscles are heavy and can increase your BMI.
Begin a cardio regimen. The key to reducing weight, and therefore BMI, is burning calories. Cardio exercise should be sustained at moderate intensity for at least 20 minutes--preferably longer--which creates a consistent calorie burn. Running, swimming, walking, rowing, and elliptical machines are examples of cardio exercise.
Lift light to moderate weight at high repetitions (lift at 70 per cent or less than your maximum strength). Lifting weights can help you lose weight since stronger muscles burn more calories as you work out. The downside is that very large muscles weigh more--muscles are approximately 18 per cent more dense than fat--so building up muscle bulk can increase weight and therefore BMI. Lifting a light to moderate amount of weight with the arms and legs for 15 or more reps will tone and build muscular stamina, allowing you to work out harder and longer, without significantly increasing bulk.
Gradually increase your workout duration and intensity. The key to losing weight and reducing BMI is constantly seeking to burn more calories at each workout. As you get in better shape, increase the difficulty of your exercises to burn calories. If you walk, increase your pace, or go farther. If you use a stationary bike, increase the resistance, or go for 10 extra minutes. The more your fitness improves, the longer and harder you can work out, which will reduce BMI.
Eat a healthy diet to complement your exercise routine. To lose weight, you must watch your calories, but you need to eat enough to have energy to work out and function. Eating three square meals a day (including a good breakfast) and focusing on whole grains, fruits, and vegetables will give you a leg up on lowering your BMI. If you don't burn off more calories than you consume, you will not lower your BMI.
Keep tabs on your weight. Since reducing BMI is essentially just reducing weight, it is important to weigh yourself, preferably every day. This will make you more conscious of your improvements and backslides, which should help feed your motivation.
BMI is not always a good measure of fitness, especially for athletes with a large amount of muscle mass. You can be very fit with a lot of muscle and be considered overweight, or even obese, on the BMI scale.