Aerobic Exercise Prescription Components

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Prescription Dependencies

Aerobic, or cardiovascular exercise prescription is dependent upon:

• fitness level
  
  • e.g.: poor, fair, average, good, excellent
  • begin at a lower intensity with lower cardio fitness and higher intensities with greater cardio fitness
  • see cardiovascular fitness tests
    
• fitness goal(s)
  
  • health
  • fat loss
  • cardiovascular performance
  • sports performance
    
• time constraints
  
  • time of day
  • time per day
  • days available
    
• exercise preferences
• equipment availability
• orthopedic limitations or concerns
  

Intensity

Intensity refers to how fast and action is performed (speed), the power or strength required to achieve an activity (watts, level, incline), or the effort put forth by the participant during the activity (exertion).
A percentage of the maximum heart rate (HRmax), METs, or maximum oxygen consumption (VO2max) can be used to prescribe exercise intensity. Heart rate reserve (HRR) which takes into account the resting heart rate can also used to prescribe exercise intensities (See Target Heart Rate Calculator).
Exclusive use of heart rate (HR) to prescribe exercise intensity may lead to errors in estimating relative exercise intensities (%VO2R), particularly when the maximum heart rate is predicted (PMHR) from age (220 - Age) instead of a direct measurement. An age predicted prescription of 60% HRR may be as low as 70% and as high as 80% of the actual HR max (Dishman 1994). Also see Heart Rate Tidbits.
Intensity can also be monitored using 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 can monitor exercise intensity using RPE (ACSM 1995).
Exercise Intensity RecommendationsIntensity (I)MethodComments
60 to 90%Maximum heart rate (HR max) or Predicted HR max (PMHR)I * direct measurement or (220 - Age)
50 to 85%VO2 maxI * direct measurement
50 to 85%METI * (VO2 max / 3.5)
50 to 85%Heart rate reserve (Karvonen formula)I * (HR max - HR rest) + HR rest
  12-16Rating of Perceived Exertion (RPE): Original 6 to 20 scaleRPE x 10 corresponds to heart rate
3-5RPE: Revised 0 to 10 scaleMore intuitive: 4 = somewhat hard
Recently, ACSM recommended VO2 Reserve as a method to prescribe exercise intensity. Gaskell et. al (2004) demonstrated %HRR is better related to %VO2max than to VO2R in 630 initially sedentary individuals (ages 17 to 65 years). Gaskell concludes %VO2max is the better measure for prescribing exercise intensity.
Maximal aerobic capacity can calculated using various aerobic fitness tests including, 1 Mile Walk, YMCA Cycle Ergometer, Maximum Treadmill, 1.5 Mile Run, 12 Minute Run. An exercise intensity can be prescribed using percent range of VO2 max or METs: Treadmill, Cycle Ergometer, or Stepping.

Fitness Level	Low			Moderate			High			Very High
Percent Max Heart Rate	50	60	66	70	74	77	81	85	88	90	92	100
Percent VO2 max	28	42	50	56	60	65	70	75	80	83	85	100

Exercise adherence may decrease if exercise intensity is too high, particularly the first 4 to 6 weeks (ACSM 1995). Intensity should increase in a gradual and systematic manner as physiological adaptation occurs. 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 minutes) excluding time spent warming up and cooling down. Initial programs may last 12 to 15 minutes and progress toward 20 minutes. Severely deconditioned individuals 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). Individuals just beginning weight-bearing exercise (eg: jogging, aerobic dance, etc.) may be advised to wait 48 hours between bouts to prevent overuse injuries. If exercising on consecutive days, alternating between two modes of exercise (e.g.: walking one day, cycling next day) can be suggested, particularly for those who are overweight or those who have had certain orthopedic injuries in the past.

Volume

The volume refers to the sum work performed in a given training phase. It includes the duration of the activity, the distance, and the number of times a bout was performed within a training period (E.g.: 40 km per week).

Mode

Activities that involve large muscle groups over prolonged periods of time offer the greatest improvement in VO2 max. These activities are rhythmic and aerobic in nature (e.g. walking, running, hiking, stair climbing, swimming cycling, rowing, dancing, skating, cross country skiing, rope jumping, etc.). An individual's skill and enjoyment of an activity are factors that will influence compliance and ultimately the desired outcomes (ACSM 1995).
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 overweight individual. A variety of different exercises may be desirable to reduce repetitive orthopedic stresses (ACSM 1995).
Classification of Cardiovascular Exercises (ACSM 1995)

• Energy expenditure is relatively low and can be readily maintained at a constant intensity
  
  • e.g. walking, cycling
  • more precise control of exercise intensity
  • ideal for deconditioned individuals
    
• Energy expenditure is dependent upon skill
  
  • e.g. swimming, cross country skiing, skating, aerobic dance, and aerobic step exercises
  • can provide constant intensity if skill is adequate
  • may be used in early stages of conditioning if fitness is adequate
    
• Intensity and skill is highly variable
  
  • e.g. racquet sports, basketball, soccer
  • provides variety and group interaction
  • carefully considered for high risk or low-fit individuals
    
    • competitive factors must be considered and minimized
      

Specificity & Cross Training

Training effects are specific to the muscle groups used during training and the type of training program implemented (Fox, McKenzie, Cohen 1975).
Cycling training improved VO2 max more when tested on the cycle than when tested on the treadmill. The training effects of running are more general than cycling training. Running improved VO2 max approximately the same extent whether measured on the cycle or treadmill (Pechar et. al., 1974)

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References

American College of Sports Medicine, (1995) Principles of Exercise Prescription, William & Wilkins, 5.
Dishman RK (1994). Prescribing exercise intensity for healthy adults using perceived exertion. Medicine & Science in Sports & Exercise. 26: 1087-1094.
Fox E, McKenzie D, Cohen K. (1975). Specificity of training: metabolic and circulatory responses. Med Sci Sports, 7(1):83.
Pechar G., McArdle W., Katch F., Magel J., DeLuca J. (1974). Specificity of cardiorespiratory adaptation to bicycle and treadmill training. J. Appl Physiology. 36(6):753-756.

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