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 plus to your health. If you’re not fit, work up to vigorous activities slowly
How can you judge the pace/intensity of your workout?
Metabolic Equivalents (METs) are commonly used to express the intensity of physical activities.
MET is the ratio of a person’s working metabolic rate relative to their resting metabolic rate.
One MET is defined as the energy cost of sitting quietly and is equivalent to a caloric consumption of 1kcal/kg/hour. It is estimated that compared with sitting quietly, a person’s caloric consumption is three to six times higher when being moderately active (3-6 METs) and more than six times higher when being vigorously active (>6 METs).
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? 
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
