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How To Use Subjective Intensity As A Physical Therapist

Table of Contents

Key Takeaways:
  • Subjective intensity is a way to measure how difficult an exercise or movement feels to an individual
  • Using subjective intensity measures allows physical therapists to adjust exercise prescriptions in real time to accommodate fluctuations in presentation
  • Objective has a time and place, but is more rigid and requires more setup that subjective intensity

What is intensity?

One of the mainstays of physical therapy intervention is and should be an intelligently structured exercise program. To achieve this, there are four training variables that need to be taken into consideration:

  1. Volume
  2. Frequency
  3. Intensity
  4. Movement Variation

Of those that seems to be overlooked the most is intensity. Simply put, intensity tells the patient (athlete) how difficult the rest of the programming variables should be applied. If we wanted to take things a step further, we could discuss the proximity to failure and how close to absolute mechanical failure of a lift we hope the patient to get to. But we aren’t going to take things a step further in that direction as that would require another blog. For now, lets stick a flag in the fact that intentisy is simply, how difficult.

There are two types of intensity: Objective and Subjective

Objective Intensity

Objective intensity describes a quantitative or measurable direction given by the coach or clinician to the athlete or patient about what exactly they need to be doing intensity wise. The most common ones used in the lifting world are percentages of rep maxes (RM) as well as specific loads to be used. A rep max comes from testing in which a certain movement is pushed to the maximum amount of load that can be completed over the prescribed amount of repetitions. A 1RM can be done with a deadlift, and the goal being to see how much load an athlete can perform for that single repetition.

Wherever they land for the most amount of load they can move for that single repetition is their 1RM. We can apply this to a 3RM, 5RM and so on. All this is a line in the sand to be draw in a specific context so that percentages of that RM can be derived from it going forward. Once a RM is set for a particular movement, the program can form around that RM. For example, a coach may prescribe a deadlift for 5 repetitions with 80% of the 1RM that was set. If that 1RM was 315lbs, the athlete would then need to complete 5 repetitions with 252lbs.

Specific loads fall more into the functional fitness or CrossFit category in which a certain element of the program needs to be done with a load prescibed by the coach. For example, a workout may require participants to perform 21 pullups, then 21 thrusters with 95lbs. The 95lbs is the specific obejctive intensity given for the workout.

Subjective Intensity

Subjective intensity is a way to measure how difficult an exercise or movement feels to an individual. It is qualitative in nature, meaning it is up to the interpretation and of the perception of the patient or athlete for themselves to decide. It allows patients to provide feedback about their perceived exertion levels during their programs. There are two common ways to measure subjective intensity: Rate of Perceived Exertion (RP) and Reps in Reserve (RIR).

Rate of Perceived Exertion (RPE)

RPE is a numeric scale that ranges from 0 to 10, with 10 representing the highest level of effort possible, where no more work can be done, and 0 indicating no effort. For example, during a back squat with 100 lbs for a set of 5, a patient might rate it as an RPE 6, indicating a moderate level of difficulty (in relation to RPE 10).

RPE seems to have originated in the 1970s with Gunnar Borg, a Swedish Psychologist who developed it in the context of the differences in change of physical work and psychological load:

“And when the physical work load is increased, the subjective force or the perceived exertion does not grow linearly with the physical load. Since man reacts to the world as he perceives it and not as it ‘really is’, it is important to know more about the relation between objective and subjective measurements of physical stress.”[1]

It has more recently been adapted by the lifting community as a flexible way to rate performance during specific tasks or sessions.

Reps in Reserve (RIR)

RIR is another subjective intensity measure that operates on a 0 to 10 scale. It quantifies how many reps an individual feels they have left “in the tank” before reaching absolute failure. An RIR rating of 3 implies that the person could do three more repetitions before failure. RPE and RIR are somewhat interchangeable and serve as valuable tools in customizing exercise programs.

Why Should Physical Therapists Use Subjective Intensity?

The need for subjective rather than objective intensity comes from the fussy nature that exists in the musculoskeletal rehab world. Pain is an inherently complex experience and in a world of non linear presentation, a non linear exercise program can be of an advantage to physical therapists. There are four main reasons why subjective intensity comes into view in the clinical exercise context:

Accounting for Daily Fluctuations:

Patients (and humans) widely vary in symptom presentation and performance on a daily, weekly and monthly basis. By using subjective intensity measures, physical therapists can adjust exercise prescriptions to accommodate these fluctuations, ensuring that the session is fluctuating with patients.

Ensuring Appropriate Dosing:

Subjective intensity helps in crafting exercise plans that are account for where the person is in their journey, in the moment. It accounts for the patient’s current condition, whether they are experiencing symptoms, and their unique activity tolerance. This flexibility prevents under-dosing, which may hinder progress or drive deconditioning while in rehab, and over-dosing, which could lead to symptom exacerbation if current activity tolerance is exceeded.

Eliminating the Need for Max Testing:

Subjective intensity eliminates the need for max testing, which can be inappropriate and stressful for patients. Imagine taking your patient with low back pain and asking to have her work up to a 1RM so that you have the information needed to write a program.

Allowing for Flexibility:

Subjective intensity offers the flexibility to adjust exercise regimens in real-time. If an exercise is perceived as too challenging or too easy, therapists can make immediate modifications, ensuring that the patient’s program is tailored to their needs.

Subjective intensity is an indispensable tool for physical therapists to provide the most effective and patient-centered care. It takes into account the ever-changing nature of a patient’s physical condition, allowing for tailored exercise prescriptions and preventing the negative consequences of under-dosing or over-dosing. By using subjective intensity, physical therapists can create a more intelligent and adaptable approach to exercise prescription. So, if you’re a physical therapist, consider incorporating subjective intensity into your clinic to ensure your exercise prescriptions are on point, making the path to health and a return to meaningful activity smoother.


  1. Borg, G. (2019). Perceived exertion as an indicator of somatic stress. Journal of Rehabilitation Medicine2(2), 92–98. https://doi.org/10.2340/1650197719702239298