Whether you are healthy or have medical issues, moderate activity is safe for most people and does plenty to improve your health. If you're in good shape, adding vigorous activities to your workouts cuts time spent exercising and is a boon to health. If you're not fit, work up to vigorous activities slowly. Higher-intensity activities raise your chances for muscle or joint injury and very slightly increase the odds of developing a serious heart problem. This applies particularly to people who are unaccustomed to physical activity, who suddenly start exercising vigorously (although the overall risk of dying from heart disease is lower than if you did no exercise).
How can you judge the pace of your workout? The easiest way to measure exertion characterizes the intensity of an activity through broad categories, such as light, moderate, or vigorous. Called perceived exertion, it's especially helpful for staying in a safe range of activity. As you improve your fitness, you'll find your perception of the intensity of a particular activity—walking up a nearby hill, for example—changes.
The table below describes physical changes at each level of exertion. If you're just getting started with an exercise program, aim for a moderate pace. (If health problems or disabilities make moderate activity impossible, simply do as much as you can.) As you build up, try a mix of moderate and vigorous activities to help build endurance. As you work out more often, you'll notice gains as exercises become easier. Whenever an activity becomes easy, boost the length of your workout or your intensity again.
How hard are you working?
INTENSITY IT FEELS YOU ARE...
Light Easy
• Breathing easily
• Warming up, but not yet sweating
• Able to talk—or even sing an aria, if you have the talent
Light to moderate You're working, but not too hard
• Breathing easily
• Sweating lightly
• Still finding it easy to talk or sing
Moderate You're working
• Breathing faster
• Starting to sweat more
• Able to talk, not able to sing
Moderate to vigorous You're really working
• Huffing and puffing
• Sweating
• Able to talk in short sentences, but concentrating more on exercise than conversation
Vigorous You're working very hard, almost out of gas
• Breathing hard
• Sweating
• Finding talking difficult