If you've worked hard to build muscle, the last thing you want to do is burn it all off with too much exercise. Cardiovascular exercise is essential for keeping your circulatory system healthy, though, so it's unwise to skip cardio altogether. The right amount of the right types of cardio can help you stay fit without sacrificing muscle strength or size.
Perform a maximum of three 30-minute cardiovascular workouts per week, advises physiologist Dr. Irv Rubenstein through Columbia University's Go Ask Alice! health-services website. Save your cardiovascular exercise for the days you don't do strength training, or perform your cardio after strength training to give your muscles the greatest chance for growth.
Add short intervals of high-intensity cardio to your moderate-intensity cardio workout. Ride a stationary bike or work out on a rowing machine for 30 minutes, with a one-minute burst of high-intensity every five minutes, for example. Run sprints instead of long distances to build your leg muscles and get your heart pumping without burning a large amount of energy.
Estimate the additional amount of calories your cardiovascular workouts will burn weekly. Increase your weekly calorie intake by an amount sufficient to provide energy for your workouts. Aim for three meals and three snacks daily, spaced three or four hours apart. Include complex carbohydrates, lean proteins and healthy fats in each meal.