High-intensity interval training is a unique type of workout structure. These fast-paced, body-drenching sessions alternate active intervals of intense exercise and periods of rest or recovery. There’s a reason that high-intensity interval training, or HIIT, is skyrocketing in popularity. For one, it’s the most time-expedient way to work out. You can get fitness benefits from HIIT workouts in as short as 10 minutes if you keep the intensity high.
What about shredding body fat? Although it seems counterintuitive, short HIIT sessions offer a fat-burning advantage over long, tedious bouts of moderate-intensity cardio. For example, an Australian study found that women who did a 20-minute HIIT routine lost six times more body fat relative to a group who did 40 minutes of moderate-intensity cardio. Now, that’s a significant difference!
Why is fat-burning greater with HIIT training? The sheer stress of high-intensity exercise forces your body to spend more time recovering afterward. Recovery takes energy and that burns calories and fat stores. For example, your body has to eliminate heat, repay the oxygen debt, shuttle lactate to the liver and more.
The extra energy expenditure and oxygen consumption your body uses to do these things is called EPOC (excess post-exercise oxygen consumption). It’s something that doesn’t happen to the same degree when you do moderate-intensity cardio. According to the American College of Sports Medicine, the extra energy expenditure after a HIIT workout is between 6 and 15% of the total calories burned during the workout.
Other Reasons HIIT is So Effective
High-intensity interval training offers significant health benefits and, as many cardiologists now acknowledge is more beneficial for heart health than steady-state exercise. For example, high-intensity interval training lowers blood pressure, reduces blood lipids, and increases insulin sensitivity, all of which bodes well for heart health.
Another benefit of short, intense cardio sessions is they help preserve lean body mass, in contrast to steady-state cardio which does not. Long periods of steady-state cardio can lead to significant muscle loss, especially if you’re not consuming enough calories and not compensating with strength training. Due to the shorter nature of HIIT workouts, you’re less likely to enter a catabolic state and lose muscle tissue.
Structuring a HIIT Training Session
One question that might come to mind is how to structure the active and recovery intervals. Should you keep the active intervals long and the rest periods short or vice versa? The way you structure the intervals depends on your goals.
Let’s suppose your main goal is to improve your endurance and aerobic capacity. In this case, you want to keep your active intervals long and your recovery time relatively short so your body doesn’t have a chance to completely recover. You could make the active or work intervals as short as a minute or two or as long as 10 minutes. The recovery interval should be around 50% and 100% of the active interval in length. For example, if the work interval was 2 minutes, the recovery interval would 1 or 2 minutes. Expressed as a ratio of active to recovery, the formula is 1: 0.5-1. This interval structure primarily targets the aerobic energy system.
Targeting Different Energy Systems with HIIT Training
What if your goal is to develop anaerobic capacity, the ability to do short, intense bursts of activity? To do this, increase the recovery time between active intervals. If you’re targeting your glycolytic system, an ideal work to rest ratio is 1: 3-5. In other words, for every minute of work, you rest between 3 and 5 minutes. For developing the ultra-short-term energy system called the creatine-phosphate system, extend the recovery time even more to a work to rest ratio of around 1: 10-15. So, if you did a minute of intense exercise, you would recover for 10 to 15 minutes before repeating.
With the ability to change the active and recovery intervals, or the work to rest ratio, high-intensity interval training is appropriate for all athletes. For example, a distance runner might use a 1: 0.5-1 ratio of work to rest, whereas a sprinter or power athlete would best be served by longer recovery intervals. For some athletes, HIIT would best serve as an adjunct to traditional training. A distance runner still needs to do some steady-state cardio due to the specific nature of their sport but aerobic HIIT training would give them some of the same benefits and challenge their body in a different way.
Another advantage interval training offers long runners is the fatigue factor. Running for long distances not only makes it harder to preserve muscle tissue but the fatigue from such long sessions lasts longer. Aerobic HIIT training is a way for runners to improve endurance without overtraining. Even if you hate to run, you can use HIIT training to boost your body’s aerobic and anaerobic capabilities, giving you more endurance or power respectfully. It can even improve your performance when you lift. After all, you need stamina and power to get the most out of your workouts.
A Versatile Way to Work Out
As you can see, you can use intervals to develop aerobic capacity as well as target short-term energy systems – your glycolytic pathway and creatine-phosphate system. The key is the length of your active and recovery intervals.
Don’t forget that rest is part of the equation too. High-intensity interval workouts aren’t mean to be a daily ritual. If you’re really pushing yourself, as you should be, you need more recovery time than average. Two to three times a week is sufficient to get the benefits. Don’t try to do one every day.
Be smart when you train. Always start with a five-minute warm-up and end with a cool-down. Bear in mind that you can use HIIT training with almost any exercises you choose and switch them regularly to challenge your body in different ways. It’s highly versatile!
HIIT is intense and you want your muscles to be warm before you begin. Also, don’t become so focused on high-intensity interval training that you ignore, arguably, the most important form of training – strength training. It’s strength-training that gives your muscles the strength and stamina to stand up to an intense HIIT workout. Having more muscle also means you’ll burn more calories when you do a high-intensity interval routine.
SimplyShredded.com. “Fit with HIIT: Science is Dropping the Hammer on Endless Bouts of Steady-State Cardio”
American College of Sports Medicine. “High-Intensity Interval Training”
OnFitness. May/June 2015. “Continuous or Interval Training?”
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