Aims

To compare the effect of a bout of high-intensity interval training (HIT) with a bout of moderate-intensity continuous training (MICT) on glucose concentrations over the subsequent 24-hour period.

Methods

Fourteen people with type 1 diabetes [T1D (duration of T1D, 8.2 ± 1.4 years)], all on a basal-bolus regimen, completed a randomized, counterbalanced, crossover study. Continuous glucose monitoring was used to assess glycemic control after a single bout of HIT (six 1-minute intervals) and 30 minutes of MICT on separate days compared with a nonexercise control day (CON). Exercise was undertaken after an overnight fast with omission of short-acting insulin. Capillary blood glucose samples were recorded before and after exercise to assess the acute changes in glycemia during HIT and MICT.

Results

There was no difference in the incidence of or percentage of time spent in hypoglycemia, hyperglycemia, or target glucose range over the 24-hour and nocturnal period (12:00 am to 6:00 am) between CON, HIT, and MICT (P > 0.05). Blood glucose concentrations were not significantly (P = 0.49) different from pre-exercise to post-exercise, with HIT (0.39 ± 0.42 mmol/L) or MICT (-0.39 ± 0.66 mmol/L). There was no difference between exercise modes (P = 1.00).

Conclusions

HIT or 30 minutes of MICT can be carried out after an overnight fast with no increased risk of hypoglycemia or hyperglycemia. If the pre-exercise glucose concentration is 7 to 14 mmol/L, no additional carbohydrate ingestion is necessary to undertake these exercises. Because HIT is a time-efficient form of exercise, the efficacy and safety of long-term HIT should now be explored.