HIIT – what is the fuss about, is it safe for me, and where do I start?

High-intensity interval training (HIIT) is an increasingly popular form of physical activity in which periods of vigorous-intensity exercise are alternated with recovery time (such as 30 seconds of running, and 10 seconds of walking). HIIT is attractive for those of us struggling to fit exercise into our schedules, as it allows for increased energy usage in a relatively short time (usually 20-45 minutes). HIIT has been seen to have great benefits to our cardiovascular, cardiorespiratory and musculoskeletal systems. It also provides physiological benefits such as blood glucose and blood pressure regulation.

Why should I consider this for type 2 diabetes management?

While to some it is a daunting challenge, HIIT provides numerous benefits for those managing type 2 diabetes. It is highly effective at increasing our metabolic response, and studies have found that HIIT aids in stabilising blood glucose levels (BGL) over time. Since we are utilising our anaerobic system for energy production, we are using energy stores in the form of glycogen, which then needs to be replenished by glucose from our bloodstream. In doing so, we can see reductions in BGL, which may assist in reducing the need for regular medications as guided by your medical team. HIIT also provides a large amount of energy expenditure throughout the session, making it a highly effective strategy for weight management and reductions in waist circumference.

As with standard moderate-intensity exercise, HIIT increases hormone responses which makes exercising for chronic disease management so important. If you are someone also managing Polycystic Ovarian Syndrome (PCOS), this is an important consideration. While HIIT can assist with the management of type 2 diabetes or insulin resistance, many people managing PCOS find HIIT to be a difficult way to manage weight, as your body does not respond to hormone release the same way as someone who is just managing type two diabetes. If this is something that may impact you, seek the advice of an Accredited Exercise Physiologist to further explain these pathways.

I have type 1 diabetes, can I do HIIT?

With appropriate considerations, the answer is absolutely! The performance of HIIT increases liver produced glucose, which contributes to hyperglycaemia both during and after exercise. While this occurs for all of us, it is more pronounced for type 1 diabetics, as there is no natural insulin response. As the body has also used a lot of the glycogen stores throughout the workout, it will replenish these using glucose from our bloodstream. This can mean a fairly fast drop in BGL and increased risk of hypoglycaemia. The increases in plasma lactate levels seen with HIIT performance can also trick the brain by masking some of the typical hypoglycaemic symptoms. With consideration to these few factors, it is important to closely monitor your BGL response, and work out the appropriate insulin correction factor (ICF) for the level of exercise you are completing.

HIIT is a great option for exercise and will carry the same benefits to cardiovascular, cardiorespiratory and musculoskeletal systems as someone without diabetes, however, you will need to continue to monitor your BGL’s throughout HIIT performance to avoid hyperglycaemic and hypoglycaemic events. It should also be considered that increases in ketone levels are an indication to avoid HIIT training, simply due to the hyperglycaemic response it generates and the risk of further increased ketones.

Where or how do I start?

HIIT training is highly accessible, but for anyone trying it for the first time, it is important to remember a few things.

• Cardiac Health - If you have cardiac concerns and are under the management of a cardiologist, it is highly recommended that you gain clearance before commencing HIIT. Following clearance, it would be a good idea to start training under an accredited exercise physiologist, as they will have knowledge of your diabetes and cardiac management.
• Injury history - As great as HIIT is, if you go from nothing to four classes a week, you are at a much higher risk of injury or re-injury as a result of reduced load tolerance. Consider old and current niggles, start with some regular walking, and seek a health professional that can manage the niggle before it becomes an impending injury.
• Tolerance - Not many people can start at the top level of a HIIT class. The main concept of HIIT is that it works to a percentage of your total capacity, meaning your first HIIT session may consist of a combination of fast and slow walking rather than heavy loaded weights. Even commencing in a class, some exercises will be much harder for some individuals than others. It is important to not compare yourself to others and don’t push past your capacity. With consistency, over time this will improve! If you have done very little exercise and want to start out with HIIT, speak to an accredited exercise physiologist and they will ensure you start at a safe and effective level.

HIIT is a wonderful form of exercise for many reasons and provides significant health benefits for the general population as well as both type one and type two diabetics. It is most important to commence properly and safely and to monitor your response to new exercise through measurement of BGL, with support of health professionals including endocrinologists, diabetes educators, GP’s and accredited exercise physiologists.

References

• Francois M.E. & Little J.P., Effectiveness and Safety of High-Intensity Interval Training in Patients with Type 2 Diabetes, 2015
• Nie Q. & Chen J., HIIT and Moderate Intensity Training on the Latest Research Progress of Type 2 Diabetes, 2018
• Almenning I., et al., Effects of High Intensity Interval Training and Strength Training on Metabolic, Cardiovascular, and Hormonal Outcomes in Women with Polycystic Ovary Syndrome: A Pilot Study, 2015
• Rooijackers H. M. et al., A Single Bout of High-Intensity Interval Training Reduced Awareness of Subsequent Hypoglycaemia in Patients with Type 1 Diabetes, 2017
• Aronson A., et al., Optimal Insulin Correction Factor in Post-High-Intensity Exercise Hyperglycaemia in Adults with Type 1 Diabetes: The FIT Study, 2019.

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