Carbohydrate and Insulin Requirements During Prolonged Fasted Exercise

This project focuses on the effectiveness of various exercise strategies on the time spent in target range during and after aerobic exercise in adults with type 1 diabetes (T1D) on continuous subcutaneous insulin infusion (CSII).

The primary objective of the protocol is to determine if a moderate basal insulin reduction (-50 percent of basal), performed 90-minutes before a 120-minute aerobic exercise session (with 5-minute breaks every 30 minutes of exercise, and a ten minute break mid-exercise), improves the time in target range compared to either a carbohydrate consumption only strategy or insulin reduction (-50 percent) and carbohydrate consumption strategy both performed at the onset of exercise in patients with T1D on CSII therapy. The time in target will be determined for both the exercise period and during a 24-hour window after the end of exercise.

In all three sessions, aerobic exercise (brisk walking) will be performed in the fasted state (minimum 8 hours after the last meal) in the early-morning. The exercise will consist of four 30-minute bouts of walking at 40-50 percent of the participant's pre-determined aerobic capacity, separated by 5-10 minute breaks. The participants exercise intensity will be monitored continuously using heart rate and activity monitors. Blood glucose and blood ketone levels will be monitored throughout exercise.

Each participant will be assigned to a sequence of the three experimental visits through a randomization process. Each exercise session will be separated by at least two days and participants will be expected to complete all sessions within ~ 12 weeks from the time of the baseline/screening visit. Participants will be instructed to apply a new continuous glucose monitor (CGM) sensor between 1-5 days prior, not to perform moderate-to-vigorous exercise 24 hours prior and refrain from caffeine and alcohol 12 hours prior to each study visit. Participants are also instructed not to eat after 2330h the night before arriving to the laboratory and not to give bolus insulin or perform temporary basal rate changes after 0200h on the morning of the exercise visit. Participants are instructed to try to arrive at the laboratory with their blood glucose between 72-270 mg/dL, with no active bolus insulin according to personal CSII device, in the fasted state. If a bolus of insulin was given prior to the exercise session, the session was rescheduled. Females of reproductive capacity performed all three visits in the early follicular phase (days 1-6 of cycle). Participants arrived at the laboratory between 0600h and 1000h. Exercise start time was between 0700h and 1045h, based on participants' choice, and the timing of exercise was kept consistent within participants.

Following each exercise session, the participant will rest for 20-minutes and then leave the laboratory. The participants glucose will be monitored for 24-hours after the standardized exercise. They will also be instructed to perform a standardized basal insulin reduction overnight to help reduce the risk of post-exercise nocturnal hypoglycemia (-20 percent from bedtime for 6 hours).