Low Intensity: 60% to 70%
This zone keeps you at a comfortably low intensity and is a good choice as a warm up or for beginners because it helps you develop aerobic fitness for more intense exercise.
Moderate Intensity: 70% to 80%
This zone kicks up the intensity, improving your body's ability to transport oxygen throughout the body and conditioning your heart. You'll burn more calories in this zone, as well. Experts often recommend working at a moderate intensity to build fitness and lose weight. This Endurance Workout is a good example of moderate intensity cardio.
High Intensity: 80% to 90%
Working in this zone takes you out of your comfort zone and allows you to burn more calories while improving your VO2 Max and raise your anaerobic threshold. This High Intensity Aerobic Intervals Workout offers an example of a higher intensity workout.
Maximum Effort: 90% to 100%
Working at this level means you're working as hard as you can, as in all-out sprints or very high intensity interval training. Most of us can only sustain this level of effort for a short period of time, making this the toughest zone and more appropriate for advanced exercisers. This Sprint Interval Workout offers an example of training at maximum effort with rests in between work intervals.
American College of Sports Medicine. (2006). ACSM's Guidelines for Exercise Testing and Prescription. Baltimore, MD: Lippincott Williams & Wilkins.