Metabolic Flexibility Unlocked: The Power of High-Intensity Interval Training (HIIT)

metabolic flexibility

Metabolic flexibility is an important component of our overall health. Simply put it’s the ability to efficiently switch between our different fuel sources; glucose and fat. The more metabolically flexible you are, the better you switch between burning fat and burning glucose. High-Intensity Interval Training, commonly known as HIIT, has been shown to be very effective at increasing our metabolic flexibility. As older adults, it is very beneficial to learn what it is and how to incorporate this training into our routines because having metabolic flexibility means the following.


  • have more stable energy throughout the day.metabolic flexibility
  • have reduced food cravings.
  • have increased fat burning.
  • more mental clarity
  • have more likelihood of a prolonged healthy lifespan.

As we know these things are harder to achieve as we get older so the more tools we have the better.
Many studies have shown that HIIT training can help to increase your metabolic flexibility.

What Exactly Is HIIT Training?

HIIT is a form of exercise characterized by short bursts of intense, all-out effort followed by brief recovery periods. This triggers various physiological responses and metabolic adaptations, including improved cardiovascular fitness, increased fat burning, enhanced muscle strength and endurance, and improved insulin sensitivity.

HIIT can be adapted to different forms of exercise. This means that even most older people can do it when it’s properly customised. You can do it with things such as running, cycling, swimming, bodyweight exercises, or strength training. My personal favourite is boxing fitness. UBX is a fitness chain that incorporates boxing, weights and cardio. At the studio I go to we have a broad range of ages from teens up to 80 year olds.
UBX HIIT workout
Above you can see a typical workout where I reach 90% of my heart rate (the red zone). Four times in the workout I max out, with recovery periods in between. My point is that you need to find an exercise that works for your current situation with respect to injuries, limitations, and preferences. Then you can work with a health professional to design a HIIT program. Let’s look a bit at how HIIT works.

Here is a bit of the science behind HIIT and metabolic flexibility.

Increased Insulin Sensitivity

Better insulin sensitivity means better blood sugar control and better metabolic health. HIIT has been researched and shown to enhance insulin sensitivity. Not just in young people, but also sedentary individuals, overweight/obese individuals, older adults, and those with existing metabolic conditions such as type 2 diabetes. The intense bursts of exercise during HIIT sessions stimulate muscle fibres to uptake glucose more efficiently, even in the absence of insulin.

Again, it’s important to note that the positive effects of HIIT on insulin sensitivity are not limited to younger individuals. A study published in the journal Medicine and Science in Sports and Exercise demonstrated that six weeks of HIIT training in older adults resulted in increased insulin sensitivity and improved glucose control.

Enhanced Fat Burning

Research has shown that HIIT can significantly increase the body’s capacity to utilize stored fat for energy. If you increase your capacity to burn fat your metabolic flexibility also increases. A study in the Journal of Applied Physiology found that HIIT significantly increased fat oxidation during exercise, meaning more fat was being utilized as a fuel source.

Another benefit is a bit more surprising. It has been found that the benefits of a HIIT session extend beyond the exercise session itself. There is an “afterburn” effect, known as excess post-exercise oxygen consumption (EPOC). Simply put this means there is an increased calorie expenditure and fat burning that occur in the hours following exercise. Studies suggest that HIIT was far more effective with this “afterburn” effect compared to continuous moderate-intensity exercise.

I can personally attest to this. When I visit UBX at 6:30 in the morning I do so in a fasted state, having my last calories by 7 pm the night before. My workout essentially depletes me of my available glucose stores and then I am in the “afterburn” zone from 7:30am until I eat my first meal around 11am. Massive fat loss occurs when I follow this, and I can get down to 11 or 12% body fat relatively easily.

Improved Mitochondrial Function

HIIT stimulates mitochondrial biogenesis. This means it increases the number and function of mitochondria within cells. Mitochondria are often referred to as the “powerhouses” of our cells. This means they are responsible for energy production, so optimizing their function through HIIT contributes to improved metabolic flexibility.

Research has shown that HIIT is particularly effective in triggering this process, resulting in an increased number of mitochondria within the muscles. Of course, the increased mitochondrial density allows for a greater capacity to produce energy during exercise and at rest.

In addition, HIIT has been found to enhance and optimise the function of existing mitochondria which leads to improved metabolic flexibility. It does this by increasing the activity of key enzymes that assist in the breakdown of glucose and fatty acids to produce ATP (energy).

This means that the body becomes more efficient in switching between different fuel sources, such as glucose and fat, depending on energy demands.


This is just a short snapshot of how HIIT can improve your metabolic health and metabolic flexibility. It is very clear that incorporating HIIT into your exercise routine can enhance metabolic flexibility, which in turn allows your body to efficiently use both carbohydrates and fats for fuel. The benefits of this are what we started off listing.

  • have more stable energy throughout the day.
  • have reduced food cravings.
  • have increased fat burning.
  • more mental clarity
  • have more likelihood of a prolonged healthy lifespan.

No matter your age, if you haven’t done HIIT sessions there is likely a safe way for you to incorporate it into your lifestyle and reap the benefits. Make sure you consult with a professional and gradually progress based on your individual capabilities. Your metabolic health and flexibility will be the benefactors.

We care deeply about your metabolic health here at Lifestyle Integration.

Subscribe to our newsletter to get our free eBook on how to manage metabolic dysfunction
The SPEED Trap: How To Reverse Metabolic Dysfunction


References available