High intensity interval training (HIIT) vs. Continuous Endurance Training: Which is better?

CV FITNESS & SUB-MAXIMAL TESTING

High intensity interval training (HIIT) vs. Continuous Endurance Training: Which is better?

One of the more frequently asked questions regarding health and fitness is “what is the most efficient way to burn fat?” I am here to shed a little light on the differences between two popular training methods for cardiovascular fitness. Today, we’ve seen a big rise in interest and popularity in a training method commonly known as “high-intensity interval training” or HIIT for short. This type of training utilizes a burst-and-recover cycle and has been favoured by more and more people over continuous aerobic exercise.  Continuous aerobic exercise or “continuous endurance training” can be defined as doing exercise for over 20 minutes at a steady rate and intensity – such as running, swimming, cycling etc.

 What exactly is HIIT all about?

HIIT is about pairing quick bouts of high-intensity exercise with minimal or low rest intervals. The idea is to do as much work as possible within a shorter timeframe and is ideal for those who have trouble finding the time to fit a full workout into their day. Training in this way has been known to help competitive athletes boost their performance, improve health of people who enjoy exercising recreationally as well as provide the benefits gained from endurance training but with shorter durations and fewer workouts. This is not to say that continuous training should be avoided but rather that it could be beneficial to include both into a weekly workout regime.

In order to make comparisons, it is helpful to know a little bit about how the body responds to aerobic exercise, how variables such as heart rate, stroke volume (amount of blood pumped per beat) and heart contractility (force of each contraction of the heart) increase blood flow and oxygen supply to meet the demands of the working muscles and how it influences maximal aerobic capacity or “VO2max”. VOX2max is a good predictor of a person’s fitness levels and is considered the upper limit for consuming, distributing and using oxygen for energy. By improving cardiovascular function, one will also see an improvement and increase in VO2max. For people with cardiovascular disease, improving cardiovascular function and VO2max are considered major goals.

So then what’s the difference?

Previously, it was thought that only long-term endurance training would yield an increase in mitochondria density. However, studies have found that mitochondria density also increases with HIIT training. Mitochondria are directly responsible for energy production and are often referred to as the “energy factory” of a cell. According to a 6-week training study by Burgomaster et al. (2008), similar increases in levels of oxidative enzymes (proteins within the mitochondria responsible for helping to produce energy or ATP within the cell) were seen amongst subjects performing a HIIT program of four to six 30 second maximal effort sprints with 4.5 minute recovery between each bout for 3 days a week and subjects who performed continuous aerobic training by cycling for 40 minutes to an hour at a steady rate of 65% VO2max for 5 days a week. By increasing these mitochondrial enzymes, this lead to improved fat and carbohydrate breakdown efficiency for fuel as well as improved skeletal-muscle metabolic function. Therefore, HIIT can produce similar physiological changes and adaptations that mimic results of continuous endurance training, though the changes occur through different signaling-pathways and occur within a shorter timeframe. Additionally, due to the nature of HIIT, muscle size is more likely to be retained in comparison to doing continuous endurance training.

What’s better for burning fat?

Onto the interesting stuff…according to a study by Perry et al. 2008, it showed that fat burning (oxidation) in the presence of oxygen was significantly higher whereas carbohydrate burning was found to be lower after 6 weeks of HIIT. Additionally, HIIT training has been noted to cause an effect known as “excess post exercise oxygen consumption” or EPOC for short. What this means is that after a workout, the muscular demands for oxygen stay elevated while the cells in the muscles restore physiology to pre-exercise levels. Simply put, you’re still going to be burning calories AFTER your work out whereas endurance training tends to yield lower EPOC values. However, it should be noted that both methods are excellent for burning fat, although relatively HIIT has been proven to burn fat in a shorter amount of time due to working out at higher intensities with minimal rest and therefore creating huge oxygen demands from the body. At the end of the day, it’s completely goal dependent so if you were to train for a marathon then there really is no better way to be prepared than to add the kilometers in your legs and therefore opting for continuous endurance training.

In conclusion, there isn’t necessarily a “better training method” because they both yield similar results with regards to physiological and metabolic functions and are simply tools in which you can use to burn fat. Incorporating a balance of both training methods into your routine would be most the beneficial approach for improving cardiovascular performance. It’s win-win!

Cheers Chris Chen

chris