How a physical therapist decides/prescribes the exercise for a patient to make meaningful changes. You may be wondering, exercise prescription?? We have heard about prescribing medication but not exercises, right? Why do I bother to spread awareness that exercises, just like medications also have a prescription? Yes, you read that right. We, physical therapists, don’t just come up with exercises and resistance that patients need to do. Its also not just a guess when we say the frequency and intensity of exercises like 10 repetitions for twice a week. Exercise is a prescription; just not written on a prescription pad! 
Things to consider while prescribing the exercise
Types of contraction:
It is important to decide what kind of functional movement you want to achieve through the prescription. Type of muscle contraction differs with each movement. Majority of functional movement includes different types of contraction involving different muscles or group of muscles. For example, sit to stand includes, isometrics of abdominal, gluts and isotonic contractions of quads, hams, and gastro-soleus. The amount of force required to perform different types of contraction is different. Also, muscles need training to perform these types of contraction smoothly. There are two major types of contractions. 1. Isometric and 2. Isotonic. Isotonic contractions are further divided into concentric and eccentric contraction. I talked in detail about the type of contraction in my previous article.
Type of Exercise:
This is mainly based on the type of injury and the patient’s ability to perform any movement. Usually, PT progresses from one to other as a patient is able to perform the range of motion. This includes PROM, AAROM, AROM, and PRE. I talked about this in detail in my previous article types of exercises.
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Aerobic Exercise:
These exercises are prescribed to patients with poor cardiovascular efficiency. It mainly utilizes oxygen throughout the exercise period. Usually, geriatric patients are good candidates for aerobic exercises. But medically complex patients, long time bedridden patients and the ones who are just starting to perform exercises are also the appropriate candidates for aerobic exercises.
Measuring the Vitals:
The important thing while prescribing the aerobic exercises is to measure heart rate and exertion level of the patient. This exercise is usually prescribed in 60% to 80% of the maximum heart rate range. You can measure it either (60% to 80% X { 220-age}) or by Karvonen method which is ({60% to 80% X (220-age-resting heart rate) } + resting heart rate).
A therapist can educate his patients regarding Borg’s scale of Rating of Perceived Exertion (RPE) or modified RPE for Aerobic exercises. He can ask the patient how they are feeling while performing exercise and ask them not to perform at the level of “very hard” or where they are unable to talk (not carrying out the full conversation but just answer a question) while performing exercises. The patient should be somewhere between 3 to 5 in original scale or 11 to 15 in modified RPE scale to exercises at 60 to 80% of maximum heart rate.
Sometimes. I just go by visible signs on patients while performing exercises. This is very useful if my patient does not allow me to check heart rate and does not rate accurately on RPE.
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Aquatic Exercise:
Who does not like to have some fun in the pool and call it an exercise session? Well, let me rephrase that, people, except few, enjoy exercising in water. These exercises are very beneficial in orthopedics settings like joint surgery, OA, inflammatory conditions (non-contagious), etc..
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Strengthening Exercise:
This is mainly your PRE. The indication of strengthening exercise is to be able to perform the functional movement with less or no physical assistance from others. Physical therapist measures repetition maximum (RM) to prescribe an effective exercise program. The repetition maximum can be based on 1 RM or for multiple repetitions.
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Stretching as Exercise:
This is important to improve flexibility. Stretching helps to lengthen the muscle fibers. PT prescribes stretching mainly to improve range of motion, to improve posture, and to regain lost function.
Few other important types of exercises are plyometrics, Tai Chi, and yoga. These exercises can improve strength, flexibility, and agility. All of these exercises should be used on an individualized basis. Exercises like plyometric improve power and strength by performing exercises with high speed. While exercises like Tai Chi and Yoga improves endurance and strength while holding the position for few seconds to a minute. That is why it is very important to know which exercises will work for a patient based on their age, gender, lifestyle, etc. Physical therapist and or exercise physiologist are the best judges to indicate this.
Since we talk about a few other important things now let’s come to the point. Here are a few major elements of exercise prescription. Remember that, physical therapists keep many things in mind prior to prescribing exercises. These are very important elements of exercise prescription.
Elements of an exercise prescription:
Overload:
It is proven that muscle fibers need to be exposed to a certain amount of force or stimulus of muscle’s original force-generating capacity, in order to improve muscle strength and thereby improve function. Usually, this stimulus is at least 60% of the muscle’s maximum force-generating capacity. To apply overload, clinician usually calculates repetition maximum (RM) for that muscle or muscle group. RM can be 1 RM or 15 RM. This is how you will get 10 or 12 or 15 repetitions on your exercise prescription.
Specificity:
As the name suggests, a clinician concentrates on specific functional task, specific muscle or muscle groups to achieve the desired result. For example, a patient with knee pain will be given exercises concentrating on knee muscles. Or when a person is unable to perform sit to stand, a clinician will concentrate on quads, abs, glutes, hams, gastro- soleus, etc. This principle states that you need to specify your treatment approach on functional tasks or group of muscles you want to change the strength of.
Functional training :
As the name suggests, this is to improve any function by concentrating on that full function rather than concentrating on individual muscle or muscle group. Usually, to perform a function, we involve the neuromuscular system and the musculoskeletal system. Functional training is more complex and requires a patient to be cognizant. Sometimes, a patient may not be able to perform functional training as the first step in rehab. So clinician will concentrate on individual muscle and then perform functional training.
Also, a clinician may not choose functional training as a first step of the plan of care. He may want to strengthen an individualized muscle. Functional training is very important as it directly concentrates and improves the function itself. Carryover from patients is also higher as they can directly relate to functions rather than exercises of muscles or joints.
Speed and power of Exercise:
This is more important if you are training or preparing your patient to go back to some sort of sports. There are researches out there indicating how muscle strength differs when you do exercises slow vs on a faster pace. Amount of force generation is significantly higher to perform high-speed exercises. Also, the requirement of endurance is higher to sustain those exercises at high speed. Some of the objective data like timed up and go determines the fall risk of an individual based on how fast a patient can perform certain activities. That is why speed and power are important. A common way to prescribe speed and power in your exercises protocol is to time a movement and overload a muscle or function.
The frequency:
Frequency is how many times a week a person should follow exercise prescription. This is usually determines based on the type of exercise. There are different recommendation out there about how to determine the frequency. I like to follow ACSM guidelines. As per ACSM, motor learning or relearning exercises should be done daily, aerobic exercises should be done 3 times a week at 60 to 85% of maximum heart rate.
Sets of Exercise :
This is how many sets of exercises a person should do. Again, there are several pieces of research out there for this. Recent studies show there is not much difference in performing one set vs three sets of same exercises unless you are training for high athletic sports. Research also shows that rather than performing one particular exercise for three sets, it is better to perform three different exercises for one set.
Duration:
This will tell you how long you should do the exercise to achieve the desired result. It depends on the type of exercises and diagnosis you are treating. Usually, guidelines for aerobic exercises are somewhere between 30 to 45 minutes plus warm-up and cool down. Now if you are treating COPD or other cardiopulmonary disorders or patients with some complex neurological condition, your patient will not tolerate a session of 60 minutes. That time, I like to break down the session in half and do twice a day.
Conclusion:
So much for simple exercise prescription!! Yes, a lot of thoughts and calculations go in before a PT comes up with an exercise prescription for a patient to follow. Again, this is a very general guideline. It can be changed based on patient needs, diagnosis and therapist’s clinical approach.
Below is a resource for recommended exercises guidelines for different age groups.
https://health.gov/paguidelines/second-edition/10things/
Hope this helps!!