Does science back up high intensity interval training?

High intensity interval training has become a popular fitness trend that promises efficiency and effectiveness in boosting metabolic health, but is there science that backs it up? Let’s learn more about this latest fitness trend with fitness nutrition Expert Courtney Ferreira.

Boasting increased metabolism, weight loss, and athletic performance, high intensity interval training, or HIIT, has been getting a lot of attention lately. In fact, it has become a bit of a buzzword that has extended beyond the athletic and sports arena and into the general public. But what does the science say about HIIT’s true benefits?

What is HIIT?

In essence, HIIT is high intensity training followed by rest, with a cycle of work and rest repeated for a relatively short amount of time. It is typically 15-20 minutes, with some people building their tolerance to reach 25-30 minutes of HIIT. The work and rest periods can vary anywhere from six seconds to four minutes. Numerous aspects of the workout can be manipulated to your preference, including:

  • Work and rest interval intensity and duration
  • Body weight or weight training
  • Type of activity
  • Number of repetitions
  • Number of sets and between set rest

High intensity is described as 90% of maximal oxygen uptake (VO2 max), which is an indicator of cardiovascular health and can be measured using a mouthpiece during exercise. Unfortunately, this accurate indicator of oxygen uptake is used mostly in a research setting and, occasionally, in sports performance settings. Determining your VO2 max in real life is not as easy, and while there are some equations that make it possible, measuring your work effort during exercise cannot be accurately determined by an equation.

In real life, you may want to aim for a perceived 9 or 10 out of 10 maximum effort as your high intensity. This can be determined using the talk test, simply being able to say only a few words at the beginning of the interval and being unable to speak at all by the end.

So what does the research show us about HIIT’s health benefits?

Most studies using treadmills or cycling to perform HIIT and typically include workouts three days a week for at least three weeks. Here are a few of the benefits shown by HIIT training.

Lower blood sugar levels

Studies showed improved insulin sensitivity as well as lower blood glucose after a meal when compared to those who perform moderate intensity exercise. Better blood sugar control indicates it may be important for preventing chronic diseases such as diabetes.

Improved physical fitness

Studies also showed improved physical fitness and greater tolerance to exercise in overweight women.  After completing 3 weeks of training 3 times a week, the training groups showed improved time to exhaustion and peak power output.

Increased fat loss

Decreased total body fat mass has also been shown in obese women as well as in young women. Consumption of protein before a HIIT sessions may also have a greater impact on fat utilization than carbohydrates eaten before the workout.

Higher post-exercise benefits

The post exercise ‘afterburn’ , or EPOC (exercise post oxygen consumption), within 24 hours were similar when comparing a continuous moderate intensity session versus a shorter high intensity training. This suggests that HIIT can give you the same metabolic benefit in a shorter amount of time. HIIT also showed greater energy expenditure  immediately after exercise compared to high intensity resistance training and aerobic exercise.

So how can you incorporate HIIT in your life?

While athletes can show a huge increase in athletic and endurance performance through accurate HIIT training, a recreationally active person will need more time to ramp up and sustain these high level workouts. Keep in mind that these workouts can lead to injury if done incorrectly, so start off with fitness professionals who can help you incorporate it into your exercise routine safely.

But don’t fret, HIIT isn’t the only type of exercise that works! In one study, moderate intensity continuous exercise showed the same improvement in abdominal fat mass when compared to HIIT. Some might consider HIIT superior in this case due to the time efficiency, however there is no wrong type of exercise as long as you actually get moving!

How can you reap some of the benefits of HIIT at home or at your gym? Don’t overcomplicate things! You can apply some of the aspects of HIIT workouts into your daily exercise routine. First, find an exercise you enjoy. If you enjoy it, you will be consistent in your physical activity. Next, add intervals – of any kind! Focus on getting your heart rate up, pushing yourself and taking small rest breaks to ensure each time you perform you are able to give it your all. Make it work for you!

If you are making steps to push yourself beyond your comfort zone, then you are improving yourself.


Courtney Ferreira, MS, RD, LDN is a Registered Dietitian based in Baltimore, MD with a passion for helping individuals reach their health and wellness through flavorful whole foods and freedom from counting calories, fat, and minutes on a treadmill. For more insightful tips on living your healthiest life from Courtney, visit her at the RealFoodCourt.