High-Intensity Interval Training (often referred to as the acronym HIIT for short), is a very specific type of training regimen focused on very brief moments of all-out exertion, followed by a much longer rest, followed by another burst of all-out exertion. This technique has been a favorite of certain trainers and weight loss coaches for some time, and it seems to be going more mainstream with widespread acceptance. But what do we really know about HIIT and what does the science behind it say?
While we will reviews what early tests have shown and what the science says so far, it is important to understand that HIIT has not been in the scientific eye all that long, so most tests are relatively new and there’s a limited amount of total data available at this point.
The Early Tests
Many of the earliest tests really looking for biological shifts as a result of a HIIT regiment took place at McMaster University in Ontario. The first group was to do one burst and then go on with a regular effort multi-minute workout several times a week while the second group would go the traditional all-out, slow, all-out, slow repetition for 4-6 minutes: the classic burst group for many HIIT exercises.
Immediately after working out both groups showed extra proteins in the blood that indicated a boost to long-term endurance. However, after six weeks only the group that stayed on conventional HIIT workouts saw that improvement maintained. This indicates that cycling nature is indeed important if you want to get the full benefit of these workouts.
Just as interesting, those who did HIIT every day showed no improvement until after they stopped, at which point endurance improved about 6%. For those doing the traditional schedule? 12% improvement.
Additional Health Benefits Confirmed
After this initial study, there were multiple universities who took up the mantle of how HIIT training to see what else worked. While there were many additional potential health benefits confirmed with this method of training, many times the headline benefits don’t come directly but come as a side benefit to something else that is a direct result of training. This is where many of the weight loss benefits come from – not directly from calories burned at the time of the training, but from long-term, biological changes that make a person less likely to overeat or snack, and that boosts the metabolism.
Many of these smaller changes often add up to a noticeable change in weight that goes above and beyond the small burst of calories that are burned during short 4 to 20-minute workouts. However, for some individuals who are already in partially decent shape, the change can be far less noticeable.
May Help Manage Type II Diabetes
One of the expected benefits the science has shown HIIT to help out with is the management of type II diabetes. The reason behind this comes back to the all-out nature of HIIT. That surge in hormones from pushing the body to its limits will generally stop insulin resistance in its tracks, and in some patients even starts rolling it back in the other direction.
This control over insulin and blood sugar levels results in a powerful ability to more successfully manage diabetes in a way other forms of exercise have not been able to prove.
More Oxygen in the Blood
One of the most notable changes in the body is the measure of oxygen in the blood, sometimes referred to as the “VO2 max.” This may directly affect endurance in a good way while also providing a wide array of positive health benefits in everyday life that include, but are not limited to, higher energy, more efficient system, and stronger immune system (better health).
Mixed Thoughts on Weight Loss
There are some mixed thoughts on how HIIT fits in most effectively with weight loss. There’s no denying that during the short work out the calorie burn is extreme, and for individuals who have type II diabetes or are pre-diabetic, the body’s reaction to stop insulin resistance or even roll it back is a powerful additional bonus that will only help all other weight loss efforts from managing appetite to other workouts.
However, there are many individuals who will burn more calories in 90 minutes in the gym than a 10 minute HIIT exercise, so completely getting rid of the previous for the latter could result in fewer calories burned and less weight loss. Proponents of the HIIT will disagree with this, and point out that if an individual doesn’t have the time to take 90 minute long walks or spend an hour in the gym, this is a great way of keeping the weight loss efforts on track without busting the schedule.
A higher level of the right hormones in the blood after a HIIT exercise has been shown to fight off various hormones that have been linked to feeling hungry – meaning while you can definitely work up an appetite with HIIT, it does seem like in the weeks that follow mindless snacking or eating will be reduced.
Fitness Does Change Effectiveness
While these workouts have been shown to have a variety of health benefits, especially with endurance, it is also important to note that HIIT is far more effective for coach potatoes and mildly or recreationally active individuals as opposed to those who are already in great health. While there are still benefits, the better a person’s health (especially at the high-level athlete level) the fewer the clear benefits since their systems are already optimized to athletics.
While it will be really interesting to see what truly long-term studies will bring back in terms of new information, ability to keep off weight, and how many of the physical fitness improvements remain long-term, for now, there is plenty of evidence to show that HIIT is a fantastic add-on to any workout program.