听力原文： Along with jogging and swimming, cycling is one of the best all-round forms of exercise. It can help to increase your strength and energy, giving you more efficient muscles and a stronger heart. But increasing your strength is not the only advantage of cycling. Because you are not carrying the weight of your body on your feet, it's a good form. of exercise for people with painful feet or backs. However, with all forms of exercises it is important to start slowly, and build up gradually. Doing too much too quickly can damage muscles that aren't used m working. If you have any doubts about taking up cycling for health reasons, talk to your doctor and ask his/her advice. Ideally you should be cycling at least two or three times a week. For the exercise to be effective, when cycling you should become a little out of breath. Don't worry if you begin to lose your breath You might think this could be dangerous and there might be something wrong with your heart, but this is simply not true. Shortness of breath shows that the exercise is having the desired effect. However, if you find you are in pain, then you should stop and take a rest. (30)