From the Heart and Stroke Foundation

So you've heard about HIIT, the quick way to get fit in 10 minutes or so a day. Sounds too good to be true, right? Well, yes and no. It's important to understand the benefits and limitations behind any new fitness trend to make sure it will actually benefit your health. Because it was originally created to help elite athletes train when they couldn't get to their intensive workouts, one thing is clear: HIIT is not for you if you are new to physical activity, only moderately active or have cardiovascular problems or risk factors.

High-intensity Interval training (HIIT) or sprint interval training is a form of cardiovascular training that mixes very high intensity bursts with very low intensity breaks and lasts from 10 to 30 minutes.

Most HIIT sessions have a 2:1 ratio, but 1:1 is also common. You exercise intensely – be it step-ups, jogging on a treadmill or skipping rope – for 20 seconds and then rest for 10 seconds. (Or you work for 20 seconds and rest for 20 seconds if you are using the 1:1 ratio.) You repeat the sequence two more times then rest for a period of about 2 minutes. Finally, you repeat the three sequences again.

The key element of HIIT is that the high intensity intervals involve maximum effort, not simply a higher heart rate. If you want to use HIIT to improve performance for a particular sport or activity, you'll need to tailor your training program to the specific needs and demands of that activity.

How does HIIT work?

  • HIIT trains and conditions both your aerobic and anaerobic energy systems. Aerobic activity includes lower intensity activities performed for longer periods of time like walking. Anaerobic activity is any activity that consists of short exertion, high-intensity movement, like sprinting in a 400 m dash.
  • HIIT causes metabolic changes that may enable you to use more fat as fuel under a variety of conditions. This will improve your athletic endurance as well as your fat-burning potential.
  • HIIT appears to limit muscle loss that can occur with weight loss, in comparison to traditional steady-state cardio exercise of longer duration.
  • To get the benefits of HIIT, you need to push yourself past the upper end of your aerobic threshold for your age and allow your body to replenish your anaerobic energy system during the recovery intervals.

General HIIT guidelines

  • HIIT is designed for elite athletes whose primary concerns are boosting overall cardiovascular fitness, endurance and fat loss, without losing the muscle mass they already have.
  • Before starting any HIIT program, you should be able to exercise for at least 20 to 30 minutes at 85% to 90% of your estimated maximum heart rate for your age, without exhausting yourself or having problems.
  • Because HIIT is physically demanding, it's important to gradually build up your training program so that you don't overdo it. Start your HIIT sessions at 10 to 15 minutes and work your way up to longer durations – but no longer than 30 minutes.
  • Always warm up and cool down for at least five minutes before and after each HIIT session. Warm up with the same activity you will be using for HIIT training, try a slow jog if you will be running or a slower paced cycle if you will be riding the bike. Work as hard as you can during the high intensity intervals until you feel the burning sensation in your muscles indicating that you have been using your anaerobic resources.
  • No matter how great you feel when you start your exercise, stick to your intervals. When you are capable of performing the entire scheduled session and still feel capable of doing more, increase your interval duration or intensity for all sets in your workout session.
  • If you experience any chest pain or breathing difficulties during your HIIT workout, stop doing all high-intensity portions of your exercise and briefly cool down by walking around before stopping your activity. If symptoms continue, seek medical help immediately.
  • If you feel faint, briefly cool down then lie down on your back and raise your legs onto a chair or against a wall in a raised position. This will prevent blood from pooling in your legs.
  • If your heart rate does not slow during your resting interval and you are still feeling breathless at the end of your recovery intervals, you need to decrease the intensity during your work intervals. If you still cannot recover during your set recovery period, HIIT may not be right for you at your current fitness level. Remember, the goal is to work to exhaustion during HIIT so you will want to feel breathless and fatigued as you progress through the workout but you still need to be in control.

If you are new to physical activity or only at a moderate level of fitness, you can boost your workout by trying these tips.

Speak to your healthcare provider about physical activity and whether HIIT is right for you and consider taking some personal training to learn how to do it properly. It's still important to continue to do your regular routine of sustained cardiovascular activity such as running on a treadmill, jogging in the park or biking on your favourite trail. HIIT is not a replacement for your regular, day-to-day physical activity.

Before starting any activity program, be sure to talk to your doctor or other healthcare professional.

This physical activity column was written by a certified personal trainer and fitness instructor and reviewed by a specialist in kinesiology.

Posted: March 2010

Heart and Stroke Foundation


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