Three-way, Cross-over Closed-loop Exercise Study

Inclusion Criteria: * Diagnosis of type 1 diabetes mellitus for at least 1 year. * Male or female subjects 21 to 45 years of age. * Physically willing and able to perform 45 min of exercise (as determined by the investigator after reviewing the subjects activity level) * Current use of an insulin pump. * Willingness to follow all study procedures, including attending all clinic visits. * Willingness to sign informed consent and HIPAA documents. Exclusion Criteria: * Female of childbearing potential who is pregnant or intending to become pregnant or breast-feeding, or is not using adequate contraceptive methods. Acceptable contraception includes birth control pill / patch / vaginal ring, Depo-Provera, Norplant, an IUD, the double barrier method (the woman uses a diaphragm and spermicide and the man uses a condom), or abstinence. * Any cardiovascular disease, defined as a clinically significant EKG abnormality at the time of screening or any history of: stroke, heart failure, myocardial infarction, angina pectoris, or coronary arterial bypass graft or angioplasty. Diagnosis of 2nd or 3rd degree heart block or any non-physiological arrhythmia judged by the investigator to be exclusionary. * Renal insufficiency (GFR \< 60 ml/min, using the MDRD equation as report by the OHSU laboratory). * Impaired liver function, defined as AST or ALT ≥2.5 times upper limit of normal, according to OHSU laboratory reference ranges. * Hematocrit of less than or equal to 34%. * History of severe hypoglycemia during the past 12 months prior to screening visit or hypoglycemia unawareness as judged by the investigator. * Adrenal insufficiency. * Any active infection. * Known or suspected abuse of alcohol, narcotics, or illicit drugs. * Seizure disorder. * Active foot ulceration. * Severe peripheral arterial disease characterized by ischemic rest pain or severe claudication. * Major surgical operation within 30 days prior to screening. * Use of an investigational drug within 30 days prior to screening. * Chronic usage of any immunosuppressive medication (such as cyclosporine, azathioprine, sirolimus, or tacrolimus). * Bleeding disorder, treatment with warfarin, or platelet count below 50,000. * Allergy to aspart insulin. * Allergy to glucagon. * Insulin resistance requiring more than 200 units per day. * Need for uninterrupted treatment of acetaminophen. * Current administration of oral or parenteral corticosteroids. * Any life threatening disease, including malignant neoplasms and medical history of malignant neoplasms within the past 5 years prior to screening (except basal and squamous cell skin cancer). * C peptide level of ≥0.5 ng/ml * Any concurrent illness, other than diabetes, that is not controlled by a stable therapeutic regimen. * Beta blockers or non-dihydropyridine calcium channel blockers. * A positive response to any of the questions from the Physical Activity Readiness Questionnaire. * Any clinically significant disease or disorder which in the opinion of the Investigator may jeopardize the subject's safety or compliance with the protocol.