High-intensity interval training (HIIT) is a fun way to keep exercise and is an efficient way to improve fitness. However, when not done properly it can lead to elevated levels of the stress hormone cortisol resulting in symptoms of physical stress, even after the exercise is done.

What Is HIIT

A HIIT workout involves short spells of intense exercise lasting anywhere from 10 to 60 seconds, followed immediately by a period of active recovery of the same length or longer. The intense sessions are repeated anywhere from between 3 and 10 times.

HIIT can be a great way to keep fit and there are many positive outcomes such as continued post-workout calorie burn and improved fasting blood glucose which can help balance blood sugar levels. There are also many mental health benefits together with fast body composition changes and a feeling of increased energy.

So what might be the problem? During HIIT the brain senses stress and releases cortisol along with other hormones, kicking into gear our natural fight or flight response. It is this response which makes HIIT such an effective workout. If we have too much cortisol in our bloodstream however our body starts to respond in a negative way and we can experience changes in mood, chronic or muscle fatigue, disruption in sleep, feelings of anxiety and a suppressed immune system which may lead to bouts of continued illness.

Too much HIIT can confuse the brain into signalling this response even when our bodies are supposed to be at rest so you may find everyday tasks leave you feeling annoyed because your brain is thinking minor day-to-day stress is life-threatening stress.

Exercise does have many mental health benefits, but if you are experiencing stress in other areas of your life, HIIT may not be the most effective way to exercise.

How to practise HIIT effectively… It’s all in the recovery during the workouts but also during the week as well. Make sure you have recovery days and introduce LIIT (Low-intensity interval training) and low-intensity workouts such as yoga.

HIIT Checklist - be sure to include the following:

• Good sleep practices • Optimum nutrition • Good hydration • Slow breathing exercises • foam rolling or massage

Research

https://www.hindawi.com/journals/jdr/2016/4073618/ https://onlinelibrary.wiley.com/doi/abs/10.1111/sms.13610 https://pubmed.ncbi.nlm.nih.gov/30210383/