Aerobic Cooldown Has Limited Impact on Hyperglycemia in Type 1 Diabetes

An aerobic cooldown after a fasted resistance exercise session has a limited effect on glucose concentration, making the strategy ineffective in treating hyperglycemia in adults with type 1 diabetes (T1D), according to a study published in Canadian Journal of Diabetes.¹

Exercise can improve health markers in people living with T1D, including aerobic fitness and blood lipid levels, mental well-being, and anxiety or depression. However, people with T1D exercise less than those without diabetes, with the risk of hypoglycemia during and after exercise causing hesitation and fear.

An alternative can be high-intensity interval or resistance exercise while fasted in the morning, which can increase blood glucose concentration and reduce the risk of hypoglycemia. At the same time, this can increase the risk of hyperglycemia, which can contribute negatively to the long-term health outcomes of someone with T1D.

The investigators hypothesized that a 10-minute cooldown on capillary glucose performed after morning, fasted resistance exercise could cause glucose to decrease in the postexercise period and reduce hyperglycemia risk.

Experimental sessions were described by the investigators. After having their capillary glucose measured, the participants underwent 7 exercises for 3 sets of 8 repetitions, resting for 90 seconds in between sets. This exercise routine was the same as that from previous studies conducted by the same authors that also examined the effect of exercise on T1D.^2,3

Exercise is known to improve aerobic fitness level, mental health, and blood lipid levels | Image Credit: zephyr_p-stock.adobe.com

For the no cooldown session (REST), the participants remained seated for 30 minutes after the resistance exercises. For the cooldown session (EX), participants had a 10-minute aerobic cooldown on a cycle ergometer, according to the investigators.

Duration and mean heart rate across resistance exercise sessions were similar. Additionally, participants were able to maintain conversations with each other during this time, which was used by the investigators as a subjective measure of exertion.

Prior to the beginning of exercise, mean (SD) capillary glucose was 8.7 (3.1) mmol/L in the EX cohort and 7.9 (3.0) mmol/L in the REST cohort (P = .07). Within the first 45 minutes of each session, capillary glucose increased similarly in EX (0.9 [1.7] mmol/L) and REST (1.3 [1.9] mmol/L; P = .3).

During the aerobic cooldown in the EX group, glucose declined by 0.6 (1.0) mmol/L; during the same period in REST, glucose increased by 0.7 (1.3) mmol/L. The investigators noted that this difference during recovery represented a significant time by treatment interaction (P = .02). Additionally, from the end of exercise until the end of the recovery period, glucose increased in both conditions.

Although the investigators found that an aerobic cooldown indeed leads to a decline in glucose levels after fasted exercise, glucose levels continued to increase as soon as the activity ceased, ultimately resulting in similar glucose levels between conditions when the recovery period ended. They partially explained this result by pointing to the short duration of the cooldown, which they noted could have been too short to have a meaningful impact on glucose levels.

A variety of existing literature shows that blood glucose concentration can increase or decrease during fasted aerobic exercise for those with T1D. However, the investigators of the present study noted that these studies lack measurements of any other changes in the participants during their exercise, including changes in free fatty acid or triglyceride levels.

Participants in the present study were asked to replicate their food intake, insulin dosage, and physical activity on corresponding days of each condition during their study; this allowed the investigators to attribute differences in glucose to the intervention while increasing the power of their statistical tests.

Alhough they recognize that the brief glucose lowering effect of a cooldown can have some utility for hyperglycemia treatment, the investigators concluded that by itself, it is ineffective at preventing hyperglycemia or blood glucose increases after fasted resistance exercise.

“The current recommendation of an aerobic cooldown used to treat postexercise hyperglycemia should be modified to recognize that a cooldown alone may not be an effective treatment for hyperglycemia when it occurs after morning fasted anaerobic exercise,” the study authors concluded.

References

1. McClure R, Carr A, Boulé N, Yardley J. An aerobic cooldown following morning, fasted resistance exercise has limited impact on post-exercise hyperglycemia in adults with type 1 diabetes: a randomized crossover study. Can J Diabetes. 2024:S1499-2671(24)00105-9 doi:10.1016/j.jcjd.2024.05.001

2. Toghi-Eshghi S, Yardley J. Morning (fasting) vs afternoon resistance exercise in individuals with type 1 diabetes: a randomized crossover study. J Clin Endocrinol Metab. 2019;104(11):5217-5224. doi:10.1210/jc.2018-02384

3. Yardley J, Kenny G, Perkins B, et al. Effects of performing resistance exercise before versus after aerobic exercise on glycemia in type 1 diabetes. Diabetes Care. 2012:35(4):669-675. doi:10.2337/dc11-1844