Exercise Prescription Principles Of Exercise Prescription

I. General Principles

Exercise prescription should always include :

a) the mode of exercise
b) the intensity of exercise
c) the duration of exercise
d) the frequency of exercise
e) the rate of progression of the patient's physical activity

These parameters should be taken into account whether you are prescribing exercise for the healthy individual or the patient with disease. In all cases, the exercise prescription should be developed with careful consideration for the individual's health history, risk factor profile, the patient's strength and flexibility, any orthopedic conditions that may exist, behavioral characteristics, personal goals and availability of exercise facilities.


II. The Prescription

Mode of Exercise

Mode of Activity : Any activity that uses large muscle groups, performing rhythmic exercise which can be sustained for 15-60 minutes of continuous exercise, and which is aerobic in nature becomes an appropriate mode of exercise activity for most patients. Activities such as walking, wogging (walking in water), jogging, jarming (moving the arms rapidly forward and backward), running, skating, bicycling, rowing and cross country skiing (Nordic Tracking) are considered to be highly aerobic activities. Some of these activities are inappropriate for cardiac patients but walking, bicyling, walk-jogging, and light rowing are usually considered appropriate for the uncomplicated cardiac patient and the non-cardiac patient.

No matter what is wrong with the patient, each session of exercise should be started with a 10-15 minute warm-up period of low intensity exercise - an exercise intensity that is lower that the steady state exercise at which the patient will be training. Cool-down should be as long as warm-up and should include a gradually declining exercise intensity than that at which the patient exercised during steady state. It is advantageous to add stretching and flexibility exercises prior to the warm-up period and following the cool-down period.


Intensity of Exercise

Intensity of Exercise : The intensity of exercise for an apparently healthy individual is usually between 40 % - 85 % of their VO2max or its equivalent in heart rate which is 55 % - 90 % of maximal heart rate. For the cardiac patient, the ideal heart rate training zone will be between 40% - 75% of the maximum symptom limited heart rate as determined from a graded exercise treadmill test.

Determining the exercise intensity for any patient is always adjusted in light of the patient's physical work capacity. For females above the age of 50 and for males above the age of 40, it is highly recommended that they undergo a graded exercise stress test (GXT). This test is most often performed on a treadmill although GXT's can be done on an ergometer. When a GXT is performed, a thorough physician will provide the following pieces of information :

This data can be used very nicely in a modified Karvonen's formula. The formula looks like this :

Target Heart Rate=[(Max HR Achieved - HR @ rest) x (Activity Fraction)] + HR @ rest

The Activity Fraction is defined as : [(.6 - .8) + (Max METs Achieved/100)]

An example of how to calculate an activity fraction is :

Activity Fraction = (.6 + (12 METs/100)) = .72

The value of .72 would be the multiplier that you would insert into the Karvonen formula.

Now let's give an example of how to use the entire Karvonen formula.

Mr. Stevenson just had a maximum symptom limited graded exercise stress test with the following data :

Resting Heart Rate Before The GXT = 70 bpm
Maximum Symptom Limited Heart Rate Achieved = 160 bpm
Maximum METs Obtained During The GXT = 10 METs
Resting Blood Pressure = 120/80
Maximum Symptom Limited Blood Pressure = 180/78
So, taking this information and inserting it into the formula to obtain the training heart rate (THR) looks like this :

THR = [(160 BPM - 70 BPM) x (.6 +(10 METs/100)) + 70 BPM]
THR = 133 BPM will be the starting heart rate for Mr. Stevenson as he begins his new exercise program.

When Mr. Stevenson begins his treadmill walking or his bicycle ergometer training program in your clinic, you will start him out performing exercise that will generate a steady state exercise heart rate of 133 beats per minute give or take 1-2 beats. This would be considered to be a safe exercise intensity because it falls nearly 30 beats below the heart rate that he had during the GXT at which he began to develop symptoms. Those symptoms during the GXT that told his physician that he was having trouble coping with the intensity may have been S-T segment depression, significant dyspnea or a grade II angina. So, if you exercise Mr. Stevenson 30 beats below the heart rate at which he developed symptoms, then in all likelihood the patient is exercising in a work intensity zone that is safe.

Frequently, physicians do not send all of the GXT data that they have compiled on your patient. There is no reason why it should not be on the referral but many times it is not. What would happen if the physician only writes on the referral the maximum METs obtained, or just the blood pressure or heart rate information. Can you write a safe exercise prescription with only partial inormation from the GXT ? Yes, fortunately you can write a meaningful exercise program even when only part of the GXT data is given to you. Lets determine how we can do this.

Case #1 :Only the heart rate data from the GXT is sent over on the referral form from the physician's office

You can use Mr. Stevenson's data in the Karvonen formula like this :
THR = [((160 BPM - 70 BPM) x .6) + 70 BPM
THR = 124 BPM

Mr. Stevenson will begin his exercise program in your clinic performing exercise at a steady state heart rate of 124 bpm.

Case #2 :Only the blood pressure data from the GXT is sent over on the referral form from the physician's office

You can use Mr. Stevenson's GXT data in the Karvonen formula like this :

Target Systolic BP (TSBP)=[((SBPmax - SBPrest) x .6) + SBPrest]
TSBP=[((180 - 120) x .6) + 120]
TSBP=156

Mr. Stevenson would reproduce an exercise intensity on the bike or treadmill that would produce a systolic blood pressure of 156 mm Hg pressure.

Case #3 :Only the maximum METs performed from the GXT is sent over on the referral form from the physician's office

You can use Mr. Stevenson's GXT data in the Karvonen formula like this :

Training MET Level=(.6 + (10 METs/100) x 10 METs
Training MET Level=7.0 METs

Mr. Stevenson will begin his exercise program in your clinic performing an exercise intensity equivalent to 7.0 METs. Published MET tables can give you the type of exercise and its intensity that is equivalent to 7.0 METs.


Duration of Exercise

The duration of exercise should always be from 15-60 minutes depending on the patient's physical work capacity. The more debilitated and untrained the patient is, the shorter the exercise session. In some cases, the patient may not even be able to exercise continuously for 15 minutes. In this case, the exercise bouts can be broken up into shorter sessions throughout the day such as 3 five minute sessions or five 3 minute sessions. This allows the patient to accumulate 15 minutes of physical training with the training sessions interspersed throughout the day. As an example of this strategy, patients with peripheral vascular disease, such as intermittent claudication, will have to exercise for short durations multiple times each day until they build a tolerance to the work requirement.

As the patient continues to exercise regularly, each session will become a little longer until the minimum of 15 minutes can be performed in a single session. Progress the patient from this point gradually until they can exercise from 30-60 minutes continuously.


Frequency of Exercise

Exercise frequency is usually 3 times per week and advanced over time until it is 5-7 times per week. Frequency is highly dependent on a patient's condition. For example, a type I diabetic should exercise 7 days per week in order to more effectively regulate their blood glucose as well as regulate the amount of insulin they must take throughout the day. Exercise training has similar effects as insulin because it, too, stimulates the transport of glucose from the blood into the working muscle cells.

However, a type II diabetic should only exercise 4-5 times per week. These patients are not totally insulin deficient. In fact, type II diabetics may actually produce normal or supernormal amounts of insulin. They suffer from a problem called peripheral resistance - i.e. - the cells of the body are not as sensitive to the effects of insulin binding to its receptor. Hence, insulin fails to stimulate the muscle cells of the body to take up glucose from the blood as effectively as in normal subjects. Therefore, the larger issue for type II diabetics is weight reduction since most of these patients struggle with obesity. The idea to exercise type II diabetics only 4-5 times per week instead of daily is : 1) to reduce the likelihood of overuse injuries in an obese and physically unfit individual ; 2) to assist the patient in reducing body mass - i.e. - the reduction of percent body fat ; and 3) to help regulate blood glucose levels. These two examples help us to understand that frequency of exercise is greatly dependent on the patient's medical condition.


Rate of Progression

Rate of progression - how fast you advance an individual in their exercise program - is one of the more artful aspects of exercise prescription. Intensity of exercise is the only other more important aspect of exercise prescription.

Again, the rate of progression is heavily dependent on the physical condition of the patient. It may take many days to several weeks to advance the exercise intensity of a patient who is very ill. Indeed, rate of progression may be almost a non-consideration if the patient is very fragile. Certainly, patients with cancer, AIDS, or end-stage renal failure can be so gravely ill that regular advances of exercise intensity are not realistic goals. In these patients, it may only be reasonable to have daily exercise at whatever intensity they can handle - a variable day-to-day change in exercise intensity because they are so ill.

In patients with whom rate of progression is a realistic goal, there are a couple of ideas to consider when progressing the exercise prescription.

  1. Increase duration of exercise before frequency and intensity. It is an acceptible exercise strategy to have the patient workup to 45-60 minutes of continuous steady state exercise per exercise bout. Once the patient begins to say the 45-60 minute exercise sessions are getting too easy to perform, then it is time to increase the frequency of exercise per week from 3 times to 4-5 times per week. However, it is highly advisable to reduce the duration of each exercise session down to 25-30 minutes per session so that the patient can tolerate the addition of 1-2 days of additional exercise. Then as the patient accomodates to the extra days of exercise, begin to gradually increase duration back to 45-60 minutes.

  2. Once the patient is exercising 45-60 minutes per day for 5 days per week, then it is time to increase the intensity of exercise. Small increases in the exercise intensity will have to accompanied by an initial reduction in duration. Patients who are working harder should be allowed to shorten their duration to 30 minutes if they were exercising between 45-60 minutes. It may also be necessary to reduce by one day the weekly frequency of exercise. Within a few days, the patient's duration can again be made longer followed by the addition of one day in the weekly frequency back up to 5 days a week.

As you can quickly see, the exercise prescription for most patients is continuously evolving. The physical therapist should first advance the duration of individual workout sessions, followed by the increase in weekly exercise frequency. Exercise intensity should be the last of the variable to be advanced.

It goes without saying that whenever the patient's exercise prescription is advanced, it is a smart practice to re-assess the patient's response to the new exercise intensity. The clinically acceptible ways to monitor the patient's response to the new prescription are such things as :

  1. Monitor the patient's heart rate to the new exercise prescription.
  2. Monitor the patient's blood pressure response to the new changes in the prescription.
  3. Teach the patient to effectively use the Borg Scale of the Ratings of Perceived Exertion (RPE). The Borg Scale is a rating scale of relative physical exertion. The numbers in the scale have descriptors telling the patient what each number means. For example, the number 13 has a descriptor of "somewhat difficult". Other numbers on the scale have descriptors like : "light", "very light", "very hard", etc. All patients should exercise at an RPE of 10-13 which is interpreted as light to somewhat difficult. Since the scale is a relative scale rather than an absolute scale, the meaning of "somewhat difficult" will be different for all patients dependent on their physical conditioning and their disease state. Because the scale is subjective, the absolute work output between two different patients will be very different. The perceived work, though, will still be 13 or somewhat hard for both patients.
  4. Teach the patient to use the dyspnea scale
  5. Teach the patient to use the anginal scale especially if the patient has a known history of cardiovascular disease.

These tools will help you to monitor the patient's response to a new change in the exercise prescription. This will keep you from having any anxiety over how the patient is tolerating the changed prescription. These tools will reassure the patient that they are being carefully monitored and will help the patient to accept the new changes to their exercise prescription. It will also keep the patient exercising in a safe manner.


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