What is HIIT?
HIIT stands for high intensity interval training. During a HIIT workout, you give your maximum effort (100%) for short bursts of time (20-60 seconds). This is followed by brief periods of active recovery or minimal effort. The maximum effort to minimum effort is often in a 2:1 ratio.
Here’s an example of a HIIT circuit. Let’s consider sprinting. After warming up, start with an all-out 20-second sprint. The sprint is then followed by a 10-second recovery (walk). You complete this at least 8 times. A total of 3 to 5 different movements will give you a 12- to 20-minute HIIT workout. Simple, right?
Why does HIIT work?
Popular teaching tells us that a workout should last an hour. At least half an hour, right? So, is a 20-minute HIIT workout really effective? To be honest, the original research showed results with just a 4-minute workout! HIIT is not just a trend or a fad. It’s here to stay. Here’s a quick review of the science:
In 1996, Izumi Tabata, PhD, published a ground-breaking study. He compared two groups of young, male physical education majors who trained 5 days a week for 6 weeks. They all trained by cycling. The first group trained at moderate intensity for 60 minutes. The second group trained at high intensity for no more than 4 minutes each day for 4 days and moderate intensity for 30 minutes for one day. 4 minutes?! At the end of 6 weeks, Dr. Tabata found that the high intensity group was more physically fit than the moderate intensity group.
But really, why?
It’s all about oxygen.
Let’s start with a little exercise physiology. Aerobic metabolism is the way your body creates energy in the presence of oxygen. On the contrary, anaerobic metabolism takes place in the absence of oxygen. (Fat gets used as energy in this state. Yes! Fat burning is associated with anaerobic metabolism!)
In general, when you first start a movement, you are using aerobic metabolism: oxygen is present. With maximum effort, your body switches to anaerobic metabolism: oxygen stores have been used up. But ironically, during a HIIT workout, your metabolism makes a third transition - from anaerobic to back to aerobic. HIIT puts even more emphasis on aerobic metabolism during rest periods, improving your body’s ability to utilize oxygen. This does not happen with longer bouts of steady, moderate effort, like jogging.
HIIT increases VO2max
In other words, HIIT improves your body’s oxygen utilization. Maximum oxygen utilization is called VO2 max, and it's the key metric used to measure cardiovascular fitness. A high VO2 max is associated with a high fitness level. Performance athletes, like CrossFitters, measure it to assess their fitness. It's also used in research studies like Dr. Tabata's. For most of us, measuring VO2max is unnecessary, but understanding it is important for all of us!
HIIT increases EPOC
After finishing your HIIT workout, your body continues to consume oxygen at a higher level. This is called excess post-exercise oxygen consumption or EPOC. It’s also called afterburn and it doesn’t happen with moderate effort workouts. Also, it lasts for hours! For example, if you start your day with a 7 AM HIIT workout, your afterburn effect can easily last until lunch. At that point, you're burning fat without even trying!
Think about EPOC as oxygen debt or the amount of oxygen required to restore your body’s normal level of oxygen. HIIT is associated with higher EPOC than moderate exercise because it engages your anaerobic metabolism more. Once your deplete your oxygen, you rely on oxygen-less (anaerobic) metabolism. The greater your requirement for anaerobic metabolism, the greater your EPOC or afterburn.
Burning calories is a bonus. Because consuming oxygen actually burns calories, the greater the EPOC, the more calories you’ll burn.
So, what are the benefits of HIIT again?
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HIIT is efficient.
Have you avoided working out because you’re struggling to carve out the time? Try HIIT! You can get an amazing workout in less than 30 minutes!
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HIIT is low-cost.
Have you felt like you have to pay for a gym membership or boutique a la carte classes to stay in shape? You don’t! With HIIT, short intervals of sprinting or cycling don’t require a gym. You can also do strength-training HIIT workouts with a circuit of movements like burpies, mountain climbers and high-knees. No equipment required!
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HIIT keeps your heart healthy.
HIIT maximizes your heart’s fitness. Period. That’s the VO2max business I was talking about above.
