“If you are in a bad mood go for a walk. If you are still in a bad mood go for another walk.” Hippocrates Circa 450 BC

I’ve seen a lot of recent interest by people wanting to know the benefits of doing shorter exercise but at a higher intensity, wondering if it works as well as longer, continuous exercise at a lower intensity. At a higher intensity, our body burns more calories and also stresses the heart and lungs more. This type of exercise has been named high intensity interval training (HIIT).

An example of a HIIT workout may look like the following:

  • A warm-up period of 10 or more minutes
  • 1-2 minutes at 80% to 90% of maximum effort
  • 1-3 minutes of recovery at 50% to 60% of maximum effort
  • Repeat the above two steps five to ten times
  • A cool-down period or 10 or more minutes

Competitive athletes (swimmers, sports with running, cyclists, etc.) have been practicing HIIT for decades as it allows them to train at or above ‘race pace’ without getting fatigued as much (it is hard to continually train at race pace), allowing them to build up their speed for when they race or compete.

In the fitness world, many people use HIIT as a time-saver, being able to exercise for less time than with continuous exercise. There has also been interest to see if the physiological changes from HIIT result in better management of disease.

A number of studies have compared the two forms of training. These studies have generally used a small number of people (20 or so), have been for a short duration (two to six weeks) and not all have controlled for the total amount of effort or calories expended. This latter point is important given how intensity can determine how many calories are burned at a specific time. These studies have shown that HIIT is either superior to or no different to continuous exercise in terms of improvements in fitness. With respect to changes in body fat and body composition, a thorough review concluded there was no difference across a range of measures. So while studies are unclear of a definite advantage for HIIT, the fact that similar benefits can occur with less exercise time does suggest that HIIT can save you time.

Where there seems to be an advantage for HIIT is in the total number of calories burned taking into account calories burned even after the exercise has stopped. Referred to as excess post-exercise energy consumption (EPOC), studies indicate that HIIT raises the body’s metabolic rate to a greater extent and this higher rate continues for hours following HIIT exercise. So even if the number of calories burned in an HIIT session is the same as in a continuous exercise session, HIIT will result in more total calories being used.

While many questions still remain, such as what are the long term effects of HIIT compared to exercising continuously at a lower intensity, including HIIT into your exercise regimen alongside continuous exercise gives you the best of both worlds and will add variety to your routine.

Some final thoughts before beginning HIIT:

  1. If exercise is new to you, begin with a few weeks to months of continuous exercise before starting HIIT. HIIT puts more stress on the body and having a foundation of continuous exercise will help reduce that stress and help prevent injury.
  2. With any exercise, there is a greater (albeit small) risk for a heart event than at rest. In addition, the higher exercise intensity the greater the risk, although there is some indication that HIIT can be beneficial for patients with heart disease. If you have heart disease or are at risk, then see a doctor before starting HIIT.
  3. As HIIT is at a higher intensity, there is also a greater risk for injury and stress to the body, and people may experience more ‘pain’ and muscle soreness. It is important to listen to your body for these signals and take rest days (or continuous exercise days) in between the HIIT workouts.
  4. If you participate in any endurance events such as >5km running, cycling or triathlons, then it is essential to continue to do lower intensity continuous exercise (even if you add HIIT) to maintain your endurance capacity.

In the next blog I will discuss why sitting too long is bad for us.

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