When training for athletic performance or simply trying to improve fitness, intensity of activity helps signal how hard the body is working. Moderate intensity training examples are walking briskly or gardening, for example. Vigorous intensity examples are jogging or jumping rope. Several methods can be used to determine whether training is moderate or vigorous (high) intensity. Numerous health organizations endorse levels and time of training intensity for athletes and others.
Exercise prescription is founded upon the F.I.T.T. principle; this acronym stands for exercise frequency, intensity, time, and type. The most critical component of the exercise prescription model typically is exercise intensity. If a person fails to meet minimal threshold values, the result can be little to no training effect, and too high an exercise intensity can lead to overtraining and even injury. Moderate- and vigorous-intensity exercise stress body systems differently; training should vary depending on the type of exercise intensity being performed. The goals of an exercise program should include target exercise intensity—moderate, vigorous, or a combination of both. High-intensity interval training involves periods of vigorous intensity exercise for 30 seconds to 3 minutes alternated with periods of slower movement to recover.
In 2013, about one-half (50.2%) of American adults met current physical activity recommendations, yet in 2014, nearly 24% reported they participated in no leisure-time activity. More men than women engage in moderate- and vigorous-intensity physical activity. Older men and women are less active in terms of either moderate- or vigorous-physical activity compared to their younger counterparts.
To help people remain fit or train for athletic competition, various organizations have set recommended guidelines for moderate and vigorous activity. The 2015 to 2020 Physical Activity Guidelines for Americans recommend either 150 minutes of moderate-intensity aerobic activity a week or 75 minutes of vigorous-intensity activity as a minimum each week. In healthy adults 18–65 years of age, moderate-intensity aerobic activity commonly equates to a brisk walk and should noticeably increase heart rate. Comparatively, in adults age 65 years and older as well as adults age 50–64 years with clinically significant chronic conditions and/or functional limitations, moderate-intensity aerobic activity corresponds to a 5 or 6 on a 10-point scale, where 0 equates to sitting and 10 equates to an all-out physical effort. The signs associated with 5 or 6 (i.e., moderate-intensity exercise) include a modest, but noticeable, increase in heart rate and breathing. In healthy adults, vigorous-intensity aerobic activity generally includes activities such as jogging and should cause noticeable increases in heart rate and rapid breathing. By comparison, for older adults, vigorous-intensity activity corresponds to a 7 or 8 on a 10-point scale. Vigorous-intensity activities in the older segment of the population produce large increases in breathing and heart rate.
Target ranges for moderate- and vigorous-intensity exercise can be established using several methods. Athletes, trainers, and researchers might use methods such as percentage of maximal heart rate (HRmax), percentage of heart rate reserve, metabolic equivalents, rating of perceived exertion, and percentage of maximal oxygen uptake reserve (VO2R). The ranges for the different classifications of moderate-intensity exercise are:
Common activities that are usually classified as moderate-intensity include bicycling on even terrain at 10 mph (16 km/h), walking at 3.0 mph (4.8 km/h), carrying/stacking wood, mowing the lawn with a push mower, and golf, if walking and carrying the clubs.
The ranges for the different classifications of vigorous-intensity exercise as measured by athletes or other professionals are:
Participation in either moderate- or vigorous-intensity exercise is relatively safe for most individuals. Nevertheless, older individuals or people who have chronic diseases might be at increased risk for an adverse event during exercise. Incorporating health assessments and medical history questionnaires can help identify conditions, risk factors, signs, and symptoms that increase risk of a cardiac event during exercise. Doctors or fitness professionals can estimate risk of complications, such as a heart attack, by asking about past and present health conditions. The questions might lead to further medical screening and exercise testing before a person engages in vigorous-intensity exercise. The process of risk stratification assigns individuals into one of three risk categories (low, moderate, or high) based on the following factors:
Individuals categorized as low risk have no signs or symptoms of and have not been diagnosed with cardiovascular, pulmonary, and/or metabolic disease. These individuals also possess no more than one cardiovascular disease risk factor. Low-risk-stratified individuals have minimal risk for an acute cardiovascular event during exercise. This population can safely participate in either moderate- or vigorous-intensity exercise.
Individuals categorized as moderate risk are those who have no signs or symptoms of and have not been diagnosed with cardiovascular, pulmonary, and/or metabolic disease, but these individuals possess two or more cardiovascular disease risk factors. People with moderate risk also could be more likely to have a heart attack or other event during exercise. Although it is appropriate for these individuals to begin a moderate-intensity exercise program, before engaging in vigorous-intensity exercise, it is recommended that they first undergo a medical examination and complete a physician-supervised exercise test.
Individuals categorized as high risk are those who have one or more signs or symptoms of or have been diagnosed with cardiovascular, pulmonary, and/or metabolic disease. High-risk-stratified individuals have a substantial risk for an acute cardiovascular event during exercise. It is strongly recommended that before engaging in either a moderate- or vigorous-intensity exercise program these individuals first undergo a medical examination and complete a physician-supervised exercise test.
Despite the fact that regular exercise confers numerous health benefits and protects against various age-related chronic diseases, an increased risk of both cardiac and musculoskeletal complications is associated with vigorous-intensity exercise. It is important to understand the risks connected with exercise and how they can be reduced. The most common exercise-related complication is musculoskeletal injury. The incidence of injury increases with exercise intensity. A minimal risk of musculoskeletal complications is linked to walking and other types of moderate-intensity physical activities. Conversely, risk of injury is elevated during vigorous-intensity activities such as jogging. Similarly, musculoskeletal problems are more pronounced in individuals who participate in competitive sports.
Individuals should participate in either moderate-intensity exercise, vigorous-intensity exercise, or a combination of both to fulfill current physical activity guidelines. It is also important to consider whether participation in vigorous-intensity exercise yields greater benefits than moderate-intensity exercise. To address this issue, the total volume of exercise energy expenditure is controlled when comparing the difference in health outcomes between moderate-and vigorous-intensity exercise training programs. Reports that have examined which is better, after controlling for energy expenditure, conclude that vigorous-intensity exercise is superior at reducing risk for cardiovascular disease and death from all causes. Furthermore, important cardiovascular disease risk factors, including insulin resistance and low cardiorespiratory fitness, respond more favorably to vigorous-intensity aerobic exercise as compared to moderate-intensity aerobic exercise.
It is unclear exactly why vigorous-intensity exercise is more beneficial. The greatest benefit accrued from vigorous-intensity exercise might be the larger improvements in cardiorespiratory fitness. It has been proposed that, for each 1 MET increase in cardiorespiratory fitness, there is an accompanying 8%–17% reduction in death rates from cardiovascular disease and all causes. Several ways in which the body's systems adapt to vigorous exercise positively affect blood pressure, thrombosis, and other heart-related risks.
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American College of Sports Medicine (ACSM), 401 W. Michigan St., Indianapolis, IN, 46202-3233, (317) 637-9200, Fax: (317) 634-7817, http://www.acsm.org .
American Heart Association (AHA), 7272 Greenville Ave., Dallas, TX, 75231, (800) 242-8721, http://www.heart.org .
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Lance C. Dalleck, BA, MS, PhD
Revised by Teresa G. Odle, BA, ELS