According to the American College of Sports Medicine recommendations regarding the quantity and quality of exercise for developing and maintaining cardio respiratory and muscular fitness, and flexibility in healthy adults, Med. Science. Sports Exercise., Vol. 30, No. 6, pp. 975-991, 1998:
"The combination of frequency, intensity, and duration of chronic exercise has been found to be effective for producing a training effect. The interaction of these factors provide the overload stimulus. In general, the lower the stimulus the lower the training effect, and the greater the stimulus the greater the effect. As a result of specificity of training and the need for maintaining muscular strength and endurance, and flexibility of the major muscle groups, a well-rounded training program including aerobic and resistance training, and flexibility exercises is recommended. Although age in itself is not a limiting factor to exercise training, a more gradual approach in applying the prescription at older ages seems prudent. . ."
Click on the links below to learn more about studies listed.
Exercise duration and intensity in a weight-loss program.
Effect of Exercise Duration and Intensity on Weight Loss in Overweight, Sedentary Women: A Randomized Trial.
Prediction of energy expenditure from heart rate
monitoring during submaximal exercise.
General Guidelines for cardiorespiratory exercise for health, fitness and weight loss
High-intensity interval training
High-intensity interval training (HIIT) is a cardiorespiratory training technique that alternates brief speed and recovery intervals to increase the overall intensity of your workout. HIIT is used by athletes and everyday exercise enthusiasts to reach performance goals and enhance fitness and well-being.
How does it work?
Most endurance workouts, such as walking, running, or stair-climbing—are performed at a moderate intensity, or an exertion level of 5-6 on a scale of 0-10. High-intensity intervals are done at an exertion level of 7 or higher, and are typically sustained for 30 seconds to 3 minutes, although they can be as short as 8-10 seconds or as long as 5 minutes; the higher the intensity, the shorter the speed interval. Recovery intervals are equal to or longer than the speed intervals.
High-intensity interval training is done at a submaximal level; around 80-95% of maximal aerobic capacity. Sprint interval training (SIT) is a type of high-intensity interval training that pushes beyond this level to 100% or more of maximal aerobic capacity, or an exertion level of 10.
What are the benefits of HIIT?
The payoffs of pushing yourself with HIIT are plentiful, and include:
Significantly increased aerobic and anaerobic fitness
Decreased fasting insulin and increased insulin sensitivity
Reduced abdominal and subcutaneous (just under the skin) fat
The surprising thing about HIIT is that it involves such a small total amount of exercise. By including HIIT in your exercise plan, you can realize remarkable results in a short amount of time, which is good news for busy people.
Is HIIT safe?
High-intensity exercise of any type brings with it a higher risk of musculoskeletal injury and cardiac events. But along with healthy subjects, HIIT has been studied as a training method for people with heart disease and congestive heart failure. Under clinical supervision, subjects were able to tolerate high-intensity intervals without negative effects. Most importantly, they experienced bigger improvements in cardiovascular function compared to those undergoing continuous moderate-intensity training.
The bottom line? HIIT may or may not be safe for you. Check with your health care provider before adding it to your exercise plan.
How can I get started with HIIT?
Choose an aerobic exercise—like stationary bicycling. Warm up for 5 minutes, and perform just a few alternating speed and recovery intervals; 3-4 of each should be plenty and will give you a feel for it; finish with an easy cool down. Here’s an example:
Exercise Intensity, Frequency and Duration
While minimal health benefits can be attained in as little as one to two sessions per week, current guidelines recommend physical activity on most days of the week (U.S. Department of Health & Human Services, 2008)
Below find the Cardiorespiratory Recommendations for Healthy Adults according to the American College of Sports Medicine (2014)
The table below shows the recommended framework for exercise intensity for healthy adults , American Council on Exercise, personal training manual (2014)
MHR=Maximum Heart Rate
HRR=Heart Rate Reserve, the reserve capacity of the heart; the difference between maximal heart rate and resting heart rate.
For example: Target intensity 70 % HRR for a person with HRmax 201 bpm and HR rest 50 bpm
Exercise HR= 70% (201-50=151) + 50
Exercise HR=155 bpm