Aerobic Exercise Prescription Components

Aerobic, or cardiovascular exercise prescription is dependent upon:

Intensity

A percentage of the predicted heart rate, heart rate reserve, or maximum oxygen consumption can be used to prescribe exercise intensity. METs (energy cost relative to rest) can also be used to initially evaluate the appropriateness of specific activities for fit individuals. The American College of Sports Medicine recommends and exercise intensity of 60 to 90% of maximum heart rate, or 50 to 85% of VO2 max or heart rate reserve (ACSM 1995). Recently, ACSM recommended VO2 Reserve as a method to prescribe exercise intensity.

Lower intensities can illicit improvements in individuals with very low initial levels of fitness. The initial conditioning stage of aerobic exercise can begin at 40 to 60% of VO2 max or HR reserve. Exercise adherence may decrease if exercise intensity is too high, particularly the first 4 to 6 weeks (ACSM 1995).

Intensity can be monitored using heart rate or rating of perceived exertion (RPE). RPE is an individual's evaluation of fatigue based on a scale from 6 to 20 or 0 to 10.. Individuals who take medications that effect heart rate may monitor exercise intensity using RPE (ACSM 1995).

Exercise Intensity Recommendations
Intensity (I) Method Comments
 60 to 90% Maximum heart rate (HR max) I * direct measurement or (220 - Age)
 50 to 85% VO2 max I * direct measurement
 50 to 85% MET I * (VO2 max / 3.5)
 50 to 85% Heart rate reserve (Karvonen formula) I * (HR max - HR rest) + HR rest
  12-16 Rating of Perceived Exertion (RPE) Original 6 to 20 scale
 Moderate to Heavy Classification of Intensity  

Intensity should increase in a gradual and systematic manner as physiological adaptation occurs. A walking program can progress in intensity by slowly increasing the speed every week or month. Other cardiovascular activities that use levels or increase by 25 watt increments may need more gradual increases in intensity by first increasing revolutions per minute (RPM) or steps per minute. After several weeks have passed, the fast RPM is reduced with a corresponding increase in level or watts.

Ultimately, the appropriate exercise intensity is safe, tolerable, and achieves the desired caloric output within the time constraints of the exercise session (ACSM 1995).

Duration

The ACSM recommends 20 to 60 minutes of continuous aerobic activity. Time constrains of the individual must be considered. Depending upon individual fitness goals, exercise sessions may be of moderate duration (20 to 30 seconds) excluding time spent warming up and cooling down. Initial programs may last 12 to 15 minutes and progress toward 20 minutes. Severely deconditioned individual may need to perform multiple sessions of short duration (~10 minutes). Duration should increase as adaptation to training occurs without evidence of undue fatigue or injury (ACSM 1995).

Frequency

Scheduling constrains of the individual must be considered. The American College of Sports Medicine recommends aerobic activity to be performed 3 to 5 session times a week. It is recommended that individuals beginning an exercise program should perform aerobic exercise 3 days per week on non-consecutive days. Severely deconditioned individual may need to perform multiple sessions of short duration (~10 minutes) (ACSM 1995).

Mode

The type of exercise chosen should be enjoyable. The risk of injury from high impact activities must be weighed when choosing exercise modalities, particularly for novice or over weight individual. A variety of different exercises may be desirable to reduce repetitive orthopedic stresses (ACSM 1995).

Classification of Cardiovascular Exercises (ACSM 1995)

  1. Energy expenditure is relatively low and can be readily maintained at a constant intensity
  2. Energy expenditure is dependent upon skill
  3. Intensity and skill is highly variable


American College of Sports Medicine, (1995) Principles of Exercise Prescription, William & Wilkins, 5.


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