Insulin and exercise

Paul has type 1 diabetes and recently joined a gym that offers morning exercise classes. He manages his diabetes with long-acting insulin (Lantus) once daily before bed and takes fast-acting insulin (Actrapid) with meals. The classes last 30 minutes and he usually attends either a morning high-intensity interval training class (HIIT) class or a morning yoga class. Paul finds that despite having an in-range blood glucose level when starting the HIIT class, his blood glucose is usually high after the class is finished. He doesn’t ever have this problem when he attends yoga class.

Paul speaks to his diabetes care team who help him understand what is going on. They explain that in most people with type 1 diabetes, blood glucose responses to physical activity can be highly variable depending on the type or timing of physical activity. As a result, it’s important to check blood glucose before, regularly throughout, and after physical activity to understand how types of exercise can affect you. Usually, adjusted carbohydrate intake or insulin doses are needed to keep blood glucose in range.  

Blood glucose spiking after high intensity (anaerobic exercise) is very common and occurs due to the body releasing stress hormones (e.g., adrenaline) which cause the liver to release glucose into the blood. Because of this, Paul sees his blood glucose rise with high-intensity exercise (HIIT) but not with lower-intensity exercise (yoga). Generally, people can try to target this by doing a lower-intensity (anaerobic) cooldown (such as walking or cycling) which will bring blood glucose levels down. Alternatively, they could discuss with their diabetes team if a small correction dose may be appropriate in these situations.   

Cathy carb counts and injects 6 units of Fiasp to cover her lunch. Her blood glucose when she set out on her run was 6.2 mmol/L. She notices her blood glucose starts to drop and after around 20 minutes her blood glucose has dropped to 3.9 mmol/L. Cathy decides to stop running and treats her hypoglycaemia with two glucose tablets. Cathy doesn’t usually have problems with hypos during her runs when she runs in the afternoon on her days off work, but often stops her lunchtime runs due to hypos.

He speaks to his diabetes specialist nurse, Anna, who agrees they need to try and avoid night-time hypoglycaemia. She explains that Rohan is experiencing post-physical activity delayed hyperglycaemia and this is mainly because of increased insulin sensitivity following physical activity. She tells Rohan that delayed hypoglycaemia usually occurs 6–12 hours following physical activity but can happen beyond that period.  

They discuss two main ways to prevent delayed hypoglycaemia from occurring:  

1. Using a temporary basal rate reduction on his insulin pump for 6–8 hours after he plays football to prevent hypoglycaemia. This temporary basal rate reduction duration could be longer if Rohan noticed he was experiencing hypos later overnight.  
2. Having a snack before bed, ideally a low glycaemic index food.  

Abbie’s diabetes team mentioned that this variability may be explained by how much insulin Abbie has on board at different times of the day. In the morning, Abbie only has her long-acting insulin on board whereas after a meal she has her long-acting insulin and her short-acting insulin on board. Insulin is needed to move glucose from the blood into the muscles so not having enough insulin on board will cause blood glucose to rise during many different types of exercise.

Abbie’s diabetes team discuss different options that might help including taking an additional short-acting insulin injection with a snack before cycling in the morning with close blood glucose monitoring afterward. They highlight how different strategies can work for different people and recommend making small changes with close monitoring to find out what works best for Abbie.