You may be confused about exactly how hard to work during cardio. You may even think that high intensity exercise is the only way to go. After all, you can burn more calories and, even better, you don't have to spend as much time doing it. But having some variety can help you stimulate all of your different energy systems, protect you from overuse injuries, and help you enjoy your workouts more.
High Intensity Cardio
For our purposes here, high intensity cardio falls between about 80-90% of your maximum heart rate (MHR) or, if you're not using heart rate zones, about a 6 to 8 on this perceived exertion scale. What this translates to is exercise at a level that feels challenging and leaves you too breathless to talk much. You're not going all out, as in sprinting as fast as you can.
There's no doubt that some high intensity training work can be helpful for weight loss as well as improving endurance and aerobic capacity. For example, a 150-lb. person would burn about 225 calories after running at 6 mph for 30 minutes. If this person walked at 3.5 mph for that same length of time, he would burn 85 to 90 calories. But, the number of calories you can burn isn't the whole story. If you do too many high intensity workouts every week, you risk:
- Overuse injuries
- Inconsistent workouts
- Growing to hate exercise
If you're doing several days of cardio each week, which is what is recommended for weight loss, you would probably want 1-2 workouts to fall into the high intensity range. You can use other workouts to target different areas of fitness (like endurance) and allow your body to recover.
Some examples of high intensity workouts:
- A 20-minute workout at a fast pace
You can use any activity or machine, but the idea is to stay in the high intensity work zone throughout the workout. You'll find that 20 minutes is usually the recommended length for this kind of workout and most people wouldn't want to go much longer than that.
- Interval Training
A great way to incorporate high intensity training without doing it continuously is by doing intervals. Alternate a hard segment (e.g., running at a fast pace for 30 to 60 seconds) with a recovery segment (e.g., walking for 1 to 2 minutes). Repeat this series for the length of the workout, usually around 20 to 30 minutes. You can learn more in my Interval Training Workouts.
Moderate Intensity Cardio
There are a variety of definitions of what moderate intensity exercise is, but it typically falls between about 70-80% of your MHR (a level 4 to 6 on this perceived exertion scale). The American College of Sports Medicine (ACSM) often recommends this level of intensity in its exercise guidelines. The lower end of this range usually incorporates the 'fat burning zone.' That means can carry on a conversation without much difficulty and you feel pretty comfortable with what you're doing.
Moderate intensity workouts have some great benefits such as:
- Comfort -- Hard workouts are, well, hard. It takes time to build up the endurance and strength to handle challenging exercise. Moderate workouts allow you to work at a more comfortable pace, which means you may be more consistent with your program.
- Better health -- Even modest movement can improve your fitness while lowering your risk of heart disease, diabetes and high blood pressure.
- More choices -- High intensity workouts will usually involve some kind of impact or, at the least, a fast pace. But, you can usually get up into the more moderate heart rate zones with a variety of activities, providing you work hard enough. Even raking leaves or shoveling snow, if you do it vigorously enough, can fall into that category.
- Walking 10,000 steps a day
- A 30 to 45-minute cardio machine workout
- A brisk walk
- Riding a bike at a medium pace
Low Intensity Activity
Low intensity exercise is considered to be below about 60-70% of your MHR, or about a level 3 to 5 on this perceived exertion scale. This level of intensity is no doubt one of the more comfortable areas of exercise, keeping you at a pace that isn't too taxing and doesn't pose much of a challenge. This, along with the idea that it burns more fat, makes this a popular place to stay. But, as we've learned, you can burn more calories if you work harder, and that's what you want for weight loss.
That doesn't mean that low intensity exercise has no purpose. It involves the kind of long, slow activities you feel like you could do all day and, even better, activities you usually enjoy such as:
- Taking a stroll
- Light gardening
- A long, slow bike ride
- A gentle stretching routine