The main purpose of this study is to find out how often low blood sugar (hypoglycemia) happens during the night after exercise in the late afternoon. The study also will see if there are any factors that can predict if low blood sugar is going to develop. Blood samples will also be drawn to measure two hormones-glucagon and epinephrine (adrenaline)-to see how they are affected by exercise. Glucagon helps to raise the blood sugar when it is low. Epinephrine causes symptoms that make the person aware that the blood sugar is low. From the blood sample, other substances in the blood may also be measured to see how they are affected by exercise.

A second purpose of the study is to find out whether exercise affects the accuracy of a continuous glucose sensor (CGMS made by Medtronic Minimed).

The study will also look at the accuracy of different home glucose meters.

Many children and adults with type 1 diabetes have a drop in the blood sugar during exercise. When someone has low blood sugar, the body tries to return the blood sugar to normal. Some studies show that after exercise, the blood sugar may drop later in the day or during the night. However, it is not known how often this happens. Also, not enough is known about how exercise affects blood sugar or the awareness of low blood sugar.

Some studies in adults have shown that exercise may affect the body's natural response to low blood sugar and exercise in the future.

For this study, each subject will have two in-patient hospital stays 1 to 4 weeks apart, each lasting about 24 hours: one with no exercise and one with a 75-minute exercise session in the late afternoon. (The order of the exercise and sedentary days will be determined at random.)

Prior to each hospital admission, each subject will keep a detailed diary of insulin use and hypoglycemia for one week.

On each of the two admissions, the insulin regimens and diet will be as similar as possible.

On each of the 2 admissions, the following will occur:

• A CGMS sensor will be inserted and calibrated.
• An intravenous catheter for the collection of blood samples will be inserted.
• Blood sugar measurements will be made with an Ultra, BD Logic, and Freestyle meter every half hour beginning at 10:00 p.m. through 6:00 a.m.
• Blood samples for glucagon, epinephrine, and glucose will be collected hourly from 10:00 p.m. to 6:00 a.m.

On the exercise day only,

• In the morning, the subject will run on the treadmill for about 5 minutes to determine the settings needed to achieve a heart rate of 140.
• Exercise will begin at approximately 4:00PM and will consist of 15 minutes on a treadmill at a heart rate of approximately 140 followed by a 5-minute rest period. This cycle will be repeated 3 more times for a total of four 15-minute exercise periods with 5-minute rest periods in between (75 minutes total). A heart rate monitor will be worn throughout the time of exercise to ascertain the effort put forth.
• BG (blood glucose) measurements will be made using the Ultra, BD Logic, and Freestyle meters (1) prior to starting the exercise, (2) during each of the 3 rest periods, (3) immediately following the exercise session, and (4) at 15 minute intervals for one hour following the completion of the exercise. Blood samples will be collected for the central lab at the times of sampling for glucagon and epinephrine.

Inclusion Criteria:

• Clinical diagnosis of type 1 diabetes for at least 18 months
• HbA1c <10.0% as measured by the DCA2000.
• Age 10.0 to <18.0 years
• Weight >36.0 kg
• BMI (body mass index) >5th and <95th percentiles for age/gender
• Stable insulin regimen for at least 1 month and not anticipating a change prior to the subject's completion of the study
• Insulin regimen involves either use of an insulin pump or Lantus (with short-acting insulin)
• NPH or Lente, if part of the insulin regimen, is given only in the morning before breakfast
• Normal hematocrit (within normal limits of local laboratory)
• Normal thyroid function (measured within the previous year)
• Parent/guardian and subject understand the study protocol and agree to comply with it
• Informed Consent Form signed by the parent/guardian and Child Assent Form signed

Exclusion Criteria:

• Insulin regimen includes Ultralente/Lente or NPH at times other than the morning before breakfast
• A recent injury to body or limb, Addison's disease, muscular disorder, use of any medication or other significant medical disorder if that injury, medication or disease in the judgment of the investigator will affect the completion of the exercise protocol
• Asthma which has been medically treated within the last year
• Current use of glucocorticoid medication (by any route of administration)
• Current use of a beta blocker medication
• Use of pseudoephedrine 48 hours prior to CRC admission (if used in the 48 hours prior to the scheduled second admission, the admission will be deferred)
• Severe hypoglycemia resulting in seizure or loss of consciousness in the 2 weeks prior to CRC admission (if a severe episode occurs within 2 weeks prior to the scheduled second admission, the admission will be deferred)
• Active infection (if at the time of the planned second admission an infection is present, the admission will be deferred)
• Anticipating a significant change in exercise regimen between admissions (i.e. starting or stopping an organized sport)