All patients with DMD have routine PFT’s every six months as standard of care. You will be randomized in to one of two groups. The group assignment will be chosen by chance, similar to flipping a coin. If you are assigned to group one you will first have your regularly scheduled PFT in the morning. You will be asked to complete a second PFT that afternoon as least 4 hours after the first PFT. You will then be asked to come back to the clinic in two weeks and repeat these PFT’s, once in the morning and once in the afternoon at least 4 hours apart. Each PFT will take approximately 10 to 15 minutes. If you are assigned to group two, you will have your regularly scheduled PFT in the morning and then a second test in the afternoon at least four hours after the first test. After the second PFT you will receive training from a Respiratory Therapist. You will receive teaching handouts to take home and an incentive spirometer and peak flow meter to practice with. You will be asked to practice these tests 2 times a day and record your results. You will then be asked to come back to the clinic in two weeks to repeat 2 PFT’s, once in the morning and again at least 4 hours later. All participants will be asked how they feel at the time of testing.