High-intensity. It’s everywhere and everyone wants in. Whether it’s running to get fit, high intensity interval training to get even more fit, or intense circuit training to become, well, superhero-like. To say high-intensity exercise is a popular, would be a very British understatement. High-intensity is huge. And only getting bigger.
So let’s take a step back. What exactly is high-intensity? And how do you know if you’re actually exercising at high-intensity? We break it down and guide you through all things high-intensity from the point of view of the health pros, who also refer to it as vigorous-intensity.
What is High-Intensity Exercise?
An alphabet soup of health institutions and organizations such as the American College of Sports Medicine (ACSM) and Centers for Disease Control (CDC), divide physical activity into three general categories: light-, moderate-, and high-intensity.123
High-intensity exercise is anything that is more challenging than moderate exercise. Exercise at the top end of that range is called very high-intensity.
How it feels: High-intensity exercise causes a substantial increase in heart rate and breathing.4 You’re breathing deep and fast, and are likely to be sweating after about 5 minutes or less.
There are several methods you can use to determine whether you’re exercising at high-intensity:
High-Intensity: How to Measure it
- RPE. Using the modified Borg Rating of Perceived Exertion scale (RPE), on which you rate your effort on a scale of 0 – 10, high-intensity exercise begins at level 7 or 8.56
On the original RPE scale, which works on a scale of 6 – 20, high-intensity exercise is 14 – 16, which is feels “hard”. Very high-intensity exercise is a 17-19, which feels “very hard” to “extremely hard”.7
- Talk test. During high-intensity exercise you are only able to say a few words at a time before pausing for breath. At very-high intensity you are out of breath and it’s difficult to talk at all. If you are able to speak in complete sentences, you’re exercising at moderate-intensity.89
- Heart rate. High-intensity exercise is between 77% and 93% of maximum heart rate (MHR), while very high-intensity is at 94% MHR and above.1011 You can use a heart rate calculator to turn these percentages into helpful numbers – the actual heart rate you should exercise at.
Read more: How to measure exercise intensity
Examples of High-Intensity Exercise
The intensity of all types of physical activity is rated using something called metabolic equivalent of task (MET). One MET is the amount of energy you burn while at rest.12
- Race walking
- Hill walking
- Hiking (cross-country, uphill, or with a heavy backpack)
- Nordic walking (fast pace or uphill)
- Cycling (hills, or 10 miles per hour or faster on flat terrain)
- Spinning classes
- Jumping rope
- Circuit training (vigorous, minimal rest)
- Step aerobics (step higher than 4 inches)
- Racquet sports (e.g. singles tennis, racquetball, squash)
- Goal sports (e.g. soccer, basketball, hockey, lacrosse)
- Heavy gardening (e.g. digging, spading, composting, chopping wood)
All the above activities are considered high-intensity activities. However, they may feel easier or harder depending on your level of fitness and where you are on your fitness journey:19
- Low level of fitness. If you have been inactive, suffer with a medical condition, or are an older adult, these activities may feel incredibly hard. This means that a slow jog, which is at the easier end of high-intensity, may feel more like maximal intensity exercise (e.g. an all-out sprint).
In this case, it is more appropriate to gauge exercise intensity by how hard exercise feels to you (i.e. talk test, perceived effort, heart rate). You should feel comfortable doing moderate-intensity activities, such as brisk walking, before moving on to high-intensity activities.20
- Increasing fitness. Once you start performing these high-intensity activities regularly, they will start to feel easier and more comfortable. This is a good thing! It’s a sign your fitness levels are growing. To keep on making progress you can use RPE, the talk test and heart rate.
If you have a health condition, talk to your healthcare provider to get the go-ahead, before starting high-intensity exercise. They will also be able to give advice about the best type of exercise and can develop a personalized physical activity plan for you.
Read more: How to find an exercise you’ll love
Benefits of High-Intensity Exercise
High-intensity exercise helps you function and feel better, and reduces the risk of many chronic diseases. An abundance of studies show that like moderate exercise, high-intensity activity has a positive effect on blood pressure, cognitive function, mental health (including depression, stress, and anxiety), wellbeing, quality of life, and some types of cancer.212223242526
The advantage, of course, is that you are able to achieve these same benefits in less time. (According to the CDC one minute of high-intensity activity is the equivalent of two minutes of moderate-intensity exercise.)27 But is there more to be gained?
- Cardiovascular disease. High-intensity activity may have a bigger impact on reducing the risk of cardiovascular disease, including coronary heart disease, than moderate exercise.313233
- Diabetes. Higher exercise intensity is associated with larger improvements in cardiorespiratory fitness and blood sugar control, in adults with type 2 diabetes.3435
- Chronic disease. High-intensity exercise appears to be more protective against chronic disease in general. Studies suggest that it is associated with a lower risk of chronic illnesses, such as heart attack, chronic lung disease, Parkinson’s disease and Alzheimer’s disease.3637
- Longevity. High-intensity physical activity may be associated with even greater reductions in the risk of premature death compared to moderate-intensity exercise, though some research has found them to be equally effective.383940
- Fitness. High-intensity exercise is superior at increasing cardiorespiratory fitness (VO2max), even when workout time is adjusted so you burn the same number of calories. Vigorous exercise is especially necessary if you are already relatively fit and want to substantially increase your aerobic fitness.414243
- Abdominal fat. High-intensity workouts may be more effective for losing belly fat (visceral abdominal fat) than than moderate-intensity exercise.44
- Weight loss. High-intensity physical activity can lead to greater weight loss, because it burns more calories in less time compared to moderate exercise. The difference in calorie burn for a 30-minute workout is significant.
For example, a 154lb person burns about 140 calories (4.7 calories per minute) walking at 3.5mph for 30 minutes, while jogging at 5mph burns 295 calories (9.8 calories per minute). In other words, jogging burns more than double the calories of walking, in the same time period. Therefore, ultimately you are likely to burn more calories with high-intensity exercise, leading to greater weight loss.4546
To lose a significant amount of weight (more than 5% of body weight) and to keep that weight off may require more than 40 minutes of moderate-intensity activity per day.4748 Given the time commitment needed, high-intensity exercise is a practical and efficient way to lose weight and prevent weight regain.
These additional benefits are about high-intensity exercise generally. However, high-intensity interval training (HIIT) specifically, confers a whole host of further benefits.
Recommended Amount of High-Intensity Exercise
To gain substantial health benefits aim for at least 75 – 150 minutes of high-intensity physical activity a week. That’s the equivalent of 25 – 50 minutes a day, 3 times a week.
- Alternatively, you can do 150 – 300 minutes of moderate-intensity aerobic activity per week, or a combination of of moderate- and high-intensity exercise. As a rule of thumb, 2 minutes of moderate-intensity activity is about the same as 1 minute of high-intensity activity.
- Exercising above these minimum guidelines leads to additional gains in health and fitness, and greater weight loss.
- If you can, try to space your workouts throughout the week.
How often? To avoid overtraining and injury, and to ensure you reap all the benefits of your hard work, limit workouts that are taxing and leave you tired (about RPE 14 and above), to 3 per week. This gives your body time to recover, which is when it rebuilds after the stress of exercise, adapts, and gets stronger. In other words, this is when the magic happens. The principle holds true whether you’re a beginner or an elite athlete.
On other days you can perform less intense workouts with an RPE of 13 or below. This creates a more well-rounded exercise plan that works and benefits your body in different ways.
How to Get Started
The name of the game is patience and prudence. High-intensity exercise is fun and exhilarating. And the rush of endorphins leaves you in a state of post-workout bliss which will have you coming back for more, again and again. But, to get there you need to do it right. That is, you need to ease into it.
When it comes to high-intensity exercise, you can’t fake ’til you make it. If you go full out straight away, you’ll simply collapse exhausted in a heap after a mere couple of minutes. You’ll think you absolutely loathe it, and probably swear off it forever.57
The answer is time. You need time to strengthen your heart and lungs, so that you’re able to sustain exercising at high-intensity. You need time to allow your joints and muscles to become stronger, which reduces the risk of injury. Time prepares your body for the strenuous demands of high-intensity exercise.
Therefore, your plan to get started depends on your level of fitness.
Start at the lower end of high-intensity exercise (RPE 14 – 16). Avoid jumping in at the deep end with very high-intensity. For example, if you’re following a run-walk plan, your running intervals should be more of a slow jog – not a fast run or sprint. As you become more fit, you can slowly increase the pace and intensity.
You can also ease into high-intensity exercise, with activities that are low impact. They are still challenging, but place less strain on your joints.
When it comes to high-intensity exercise take it slow and steady, and you’ll see your strength grow and your fitness levels soar to new, unimagined heights. Or as Tolstoy wrote, “The two most powerful warriors are patience and time.”