A recent review of epidemiological studies and clinical trials supports this view 9. Several epidemiological studies compared moderate-intensity exercise (usually defined in these studies as 4.0 to 5.9 METS, with 1 MET being resting energy expenditure) with vigorous-intensity exercise (≥6 METS) and consistently found a lower incidence of heart disease in individuals who exercised at the vigorous-intensity rather than the moderate-intensity level. Clinical trials also showed that exercise performed at a vigorous intensity may provide greater improvements than moderate-intensity exercise in some CHD risk factors, such as increased aerobic fitness, decreased resting blood pressure, and improved glucose control. Interestingly, the review found no difference in weight loss for individuals performing moderate-intensity versus vigorous-intensity exercise. When it comes to weight loss, a calorie is a calorie, regardless of how it is burned. But for aerobic fitness and CHD risk, not all calories are created equal. Further research is needed to explore the effect of various exercise intensities on individual CHD risk factors, but the current evidence supports greater improvements with vigorous-intensity compared with moderate-intensity exercise.
Cautions Regarding Vigorous-Intensity Exercise
During exercise, sympathetic drive increases to stimulate increased heart action. The greater the intensity of exercise, the greater is the increase in sympathetic stimulation. While this stimulation is needed to increase heart rate (HR) and cardiac contractile force, other results include increased blood pressure and an increased tendency for the heart to experience rhythm disturbances. In a person who does not have heart disease, these changes are not considered dangerous. However, a person who already has CHD becomes more susceptible to a heart attack and to serious arrhythmias during exercise, especially if the intensity is vigorous. One study found that when sedentary individuals with CHD suddenly exercised vigorously (≥6 METS), their risk for experiencing a heart attack increased more than 100-fold above rest 10. However, this increased risk was only about twofold for those who normally exercised several times per week. Therefore, although exercise is beneficial to cardiac patients, professionals need to be cautious when first beginning exercise programs for those who have, or may have, CHD.
When prescribing vigorous-intensity exercise, one also must be aware of a higher risk for musculoskeletal complications and overuse injuries, particularly with modes of exercise that involve significant impact, such as running. Increases in intensity should be done gradually and in a periodized manner. For example, when first increasing intensity, decrease the duration or frequency so that total volume remains constant. After the client has adjusted to the higher intensity, volume may increase if desired.
Another concern is the potential effect of exercise intensity on adherence. Some clients may find higher intensities of exercise uncomfortable. In such cases, it is better to maintain a moderate intensity and increase duration, as exercise of a moderate intensity that is actually performed is more beneficial than exercise of a vigorous intensity that the client chooses not to do 11.
Recommendations for Exercise Prescription
Appropriate intensity ranges for aerobic training are presented in the Table. Accumulating sufficient weekly caloric expenditure at a moderate intensity of exercise (40% to 59% O2R) is effective for sedentary individuals to achieve weight loss goals, make modest improvements in aerobic fitness, and experience some reduction in CHD risk. For weight loss especially, building up to 1 hour per day of walking or other activities of a moderate intensity is recommended. Individuals who have symptoms of heart disease or who know that they have CHD, other cardiovascular diseases, diabetes, or pulmonary disease need physician clearance before beginning even moderate-intensity exercise 11.
Individuals interested in increasing their fitness and gaining additional cardiovascular benefits should progress to a vigorous level of intensity, provided they can do so safely. Individuals with symptoms or disease should not consider vigorous-intensity exercise until having completed a physician-approved, moderate-intensity exercise program and obtained further clearance to increase intensity. Moreover, individuals who are without symptoms or disease, but who have a high risk for CHD, may begin a moderate-intensity exercise program but should seek physician clearance before beginning vigorous-intensity exercise 11. Although most clients can eventually enter a vigorous-intensity program, only individuals who are young (men, <45 years; women, <55 years) and have a low risk for CHD (no more than one major risk factor) should do so without first obtaining physician clearance 11.
Once ready to progress to vigorous-intensity exercise, individuals should be prescribed three to five sessions per week of 20 to 60 minutes at 60% to 85% O2R 11. As described in the side bar, this intensity can be translated to a target HR using the HRR method. Vigorous exercise sessions may be interspersed with moderate-intensity physical activities and recreational pursuits to provide a well-rounded regimen.
For the greatest increases in aerobic fitness, individuals already engaging in vigorous exercise should consider replacing one or two exercise sessions per week with aerobic intervals. After an extended warm-up (e.g., 20 minutes), choose an intensity of exercise that can be maintained for no more than 5 minutes, and that causes HR to rise to 90% to 100% HRR by the end of the interval. Maintain an even pace throughout the interval, rather than sprinting at the end. Then perform an equivalent period of time at a light intensity to recover for the next interval. The goal is to pace oneself so that subsequent intervals can be performed at the same near-maximal intensity for four to six repetitions. Aerobic interval training is stressful and should not be performed for extended periods of training. Typically, one would perform aerobic intervals for a period of 4 to 6 weeks with a reduced total volume of exercise, as these sessions replace other exercise bouts, as opposed to being added to the current training.
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Keywords:© 2006 American College of Sports Medicine
Exercise; Heart Disease; Prevention; Blood Pressure; Physical Activity