Fasted High-Intensity Interval and Moderate-Intensity Exercise Do Not Lead to Detrimental 24-Hour Blood Glucose Profiles

Sam N. Scott; Matt Cocks; Rob C. Andrews; Parth Narendran; Tejpal S. Purewal; Daniel J. Cuthbertson; Anton J. M. Wagenmakers; Sam O. Shepherd


J Clin Endocrinol Metab. 2019;104(1):111-117. 

In This Article

Abstract and Introduction


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.


Clinical guidelines recommend that people with type 1 diabetes (T1D) perform at least 150 minutes of moderate-intensity physical activity per week.[1] However, a single bout of moderate-intensity exercise in peoplewithT1D is associated with marked decreases in blood glucose concentrations and thus an increased risk of hypoglycemia.[2,3] The potentially large drop in blood glucose during exercise and the associated fear of acute and nocturnal hypoglycemia means that many patients avoid exercise,[4] with long-term cardio-metabolic health consequences. Safe and effective alternative forms of exercise that minimize the perceived barriers to exercise are needed for people with T1D.

Lack of time has also been cited as an important barrier to exercise in people with T1D.[4] High-intensity interval training (HIT), consisting of repeated bouts of high-intensity exercise interspersed with low-intensity recovery, is purported as a time-efficient alternative to traditional moderate-intensity continuous training (MICT) in various groups without T1D.[5] Indeed, because the typical weekly training volume during an HIT program is approximately one-third of the time commitment required for MICT,[6] HIT is able to minimize a perceived "lack of time" as a barrier to exercise. Importantly for people with T1D, the addition of short bursts of high-intensity exercise at regular intervals during a bout of MICT has been shown to assist in stabilizing blood glucose concentration during exercise and can prevent hypoglycemia during and up to 2 hours after exercise.[7,8] It has been proposed that the increase in plasma catecholamines, growth hormone, and cortisol during vigorous exercise (>80% maximum oxygen consumption) may offset the glucose-lowering effect of MICT.[8,9] Therefore, in people with T1D, HIT may maintain blood glucose concentrations and reduce the risk of hypoglycemia both during exercise and overnight. To date, however, this has not been investigated.

To determine whether HIT maintained normoglycemia both during exercise and in the 24 hours after exercise, we examined the effects of a single bout of HIT and MICT after an overnight fast on acute and 24-hour glucose concentrations in people with T1D compared with a control day without exercise (CON). Continuous glucose monitor data were analyzed to assess 24-hour glycemic control after exercise under controlled diet conditions using the most recent guidelines.[10] Capillary blood sampling was used to assess change in blood glucose concentrations during the exercise bouts. We hypothesized that blood glucose concentrations would be maintained after HIT and that the incidence and time spent in hypoglycemia would be lower compared with MICT.