Determining the Appropriate Intensity of Exercise to Prevent Post-exercise Hypoglycemia in Persons Living With T1D

Sedentary Arm: This portion of the study is complete. 10 participants completed the study in its entirety. Maximal exercise testing utilized a Parvomedics Metabolic cart to analyze oxygen consumption in ml/kg/min and maximum heart rate. Results from this test were used to estimate intensity using heart rate for the exercise sessions. Prior to each exercise session, participants arrived at 4:00 PM ate a Glucerna bar (to prevent drastic falls in glycemia with exercise) and had an IV inserted. A total of six blood samples were taken at each session at the following timepoints: (1) 0 mins-baseline, (2) 10 mins- end of warm up, (3) 35 mins-end of intervals, (4) 45 mins-end of exercise, (5) 75 mins-mid recovery, and (6) 105 mins-end of exercise. Each blood draw was sampled for glucose, cortisol, and growth hormone. Before exercise, blood glucose was measured on a handheld glucometer. If blood glucose was <5.7 mmol/L glucose was administered via Dex4 tablets. Exercise did not begin until blood glucose was at least 5.7 mmol/L. If blood glucose was greater than 16.7 mmol/L but less than 20.0 mmol/L ketones were tested on a urine ketone strip. If ketones were negative or trace exercise began.

The first exercise session was 45 minutes of moderate intensity exercise at 45-55% of heart rate reserve (HRR). The intensity determined from this session (speed and incline) was used as the recovery intensity for the high intensity sessions. The high intensity sessions were allocated in a random order from www.random.org where 1=70%, 2=80%, and 3=90%. Each high intensity session started with 10 minutes of moderate intensity exercise (at the same speed and incline from the first session) and six one minute bursts of high intensity every four minutes followed by a 10 minute cool down.

Because of the small sample size and non-normal glucose profiles, data was analyzed using a Friedman analysis of variance (non-parametric test).

Active Arm: This portion is still recruiting participants. The procedures for this experiment are very similar to the sedentary component. Blood glucose targets prior to exercise are the same however no blood samples will be taken. Participants will arrive at the lab for 4:30 PM and eat a Glucerna bar (to avoid drastic falls in glycemia with exercise). The two exercise sessions, moderate and 90%, will be allocated in a random order from a coin flip where heads is moderate exercise and tails is the 90% intervals. The moderate intensity session will consist of 45 minutes of exercise at 45-55% of HRR. The 90% session will consist of 15 minutes of moderate intensity at 45-55% of HRR followed by six one minute bursts of exercise at 90% of HRR every two minutes followed by a 10 minute cooldown.

Data will be analyzed using a general linear model and logistic regression.

Inclusion criteria

• Persons with type 1 diabetes
• Hemoglobin A1c <9.9%
• Diabetes duration >/= 2 years
• Sedentary Participants: participate in <150 minutes of moderate to vigorous physical activity per week
• Active Participants: regular performance of vigorous physical activity >3 times/week for over one year. Display a maximal oxygen uptake that is at least 40.9 ml/kg/min for females, and 49.3 ml/kg/min for males.

Exclusion criteria

• HbA1c ≥9.9% as the lack of compliance with insulin suggests they may not be able to comply with the prescribed exercise requirements
• Have frequent and unpredictable hypoglycemia as they will be at a greater risk of serious hypoglycemic events
• Had a change in insulin management strategy, including adoption of a pump within two months of enrolment or switching back to multiple daily injections in the last two months, as they may be at risk for a hypoglycemic event due to the novel insulin management approach
• Have conditions that would render vigorous intensity activity contraindicated including: uncontrolled hypertension: BP >150 mm Hg systolic or >95 mm Hg diastolic in a sitting position; severe peripheral neuropathy; or history of cardiovascular disease
• Cognitive deficit resulting in an inability to provide informed consent
• Are currently taking beta-blockers as this would limit the ability to achieve target heart rates within the prescribed range
• Are currently being treated with medications (other than insulin) that alter glucose metabolism (i.e. atypical antipsychotics, corticosteroids)
• Are women who are pregnant, breastfeeding, or planning to get pregnant
• Have a job or profession that involves shift work (working during the night time, and being asleep during the daytime, as this alters glucose levels.