HIIT or High Intensity Interval Training is, as the name suggests, a higher intensity, interval-based version of standard aerobic workouts that typically involve a consistent pace without breaks in-between. HIIT training impacts your body's physiology in a number of key ways. See how it impacts your individual markers below.
HIIT training can have a compounding effect on weight loss through an increased production of epinephrine and norepinephrine. These hormones have been shown to drive lipolysis (the breakdown of fat). Specialized adrenergic receptors on fat cells are known to activate fat breakdown, and more of these receptors have been found deep in the abdomen (surrounding visceral fat). It is assumed that HIIT could thus help reduce abdominal fat beyond other types of fat. (1)
There is also the after-burn effect of more oxygen being required by the body to return to normal levels after HIIT training that causes the body to burn the same amount of calories in half the time spent on moderate intensity aerobic training. (2)
Insulin sensitivity, the opposite of insulin resistance, has been shown to increase after high intensity exercise. This is due to muscle contractions being able to stimulate glucose shuttle transporters to take up glucose into the working muscle from the blood, whether insulin is available or not. Studies suggest that insulin sensitivity improvements of 23% to 58% can be observed in 2 week to 16 week periods (1)(2).
Scientists suggest that high intensity training with a correlated and accompanying moderate decrease in body fat (or body weight) can lead to improvements in total cholesterol, LDL cholesterol and blood triglycerides levels. (2) (3)
The type of movement is not as important as the structure of how you perform the movement(s). All HIIT training is structured in the following format:
- An INTERVAL of a specific movement (biking, sprinting, stairs etc) for a short interval of time (20 - 120 seconds)
- A REST period in-between intervals (20 - 60 seconds).
- REPEAT of the above for a specific number of SETS (i.e. number of repetitions).
It’s important to note that during each interval you should reach maximal exertion (typically 80 - 90% max heart rate). You don’t have to be an athlete to do HIIT training. Any workout can be structured as HIIT training.