High-intensity Interval Exercise Compared With Continuous Moderate Exercise on Glycemia in Postabsorptive vs. Postprandial State in Adults With Type 1 Diabetes

Participants were tested at the laboratory during one inclusion visit followed by 4 intervention visits separated by at least 48 hours and 4 weeks maximum. During the inclusion visit, participants completed the YMCA submaximal cycle-ergometer (Excalibur Sport, Lode B.V.) test to estimate maximal aerobic power (MAP), which was then used to determine subsequent exercise workloads. The test started at 25 W (50 rpm), with increasing power outputs derived from the first-stage heart-rate response. The 3-min stages continued until steady-state heart rate achieved 85% of maximal heart rate minus 10 bpm, with a 1-min extension if heart rate varied by >5 beats·min-¹ between minutes 2 and 3. Participants completed questionnaires about physical activity levels, barriers to physical activity, quality-of-life and hypoglycemia awareness. The next four experimental visits in randomized order consisted of the two aerobic exercises (i.e. high-intensity interval exercise, HIIE and moderate-intensity continuous exercise, CONT), each performed under two different prandial conditions, postprandial (PP) and postabsorptive (PA) state. A triaxial accelerometer (ActiGraph, wGT3X-BT, 30 Hz, epoch set at 60 sec) was worn on the hip from wake-up until bedtime for the day before, during and after each experimental visit. Participants were also asked to record the time, type and amount of food consumed, with the option of photographing meals, as well as in case of multiple daily injection doses/timing of insulin (rapid- and long-acting), the 24 hours before, during and after each visit. Exercises were performed on a cycle ergometer (Excalibur Sport, Lode B.V.) and were matched for total mechanical load and total duration. Both exercises began with a 3-min warm-up at 20% of MAP and ended with a 2-min active recovery at 20% of MAP. The HIIE protocol consisted of ten 1-min intervals at 100% of MAP, each interspersed with 1-min of passive recovery. The CONT protocol consisted of continuous exercise at 50% of MAP for 20 minutes. For the postprandial state, exercise began 1.5 hours after the start of lunch and the corresponding meal-related bolus/rapid-acting insulin, (i.e., in the early afternoon). For the postabsorptive state, exercise began 5 hours after the start of lunch, (i.e., in the late afternoon). Participants were instructed to follow their habitual pre-exercise routine and to replicate, as closely as possible, the same lunch and dinner on the days of the experimental visits. The measurements included: oxygen uptake, heart rate, rate of perceived exertion, muscle vasoreactivity during exercise; capillary glycaemia and lactataemia at several time points during exercise; continuous glucose monitoring data from the personal (used in daily life) device of the participants.

Inclusion criteria

• Between 18 and 60 years of age
• Regular practice of physical activity (at least 2 training sessions/week for at least 3 months)
• Diagnosis of type 1 diabetes for >1 year
• No change in insulin delivery method (i.e., multiple daily injections [MDI], continuous subcutaneous insulin infusion [CSII] in open or closed loop) over the previous 3 months
• Use of a continuous glucose monitoring (CGM) device in daily life

Exclusion criteria

• Diabetes-related complications except for background retinopathy