Enter the maximum heart rate during exercise, resting heart rate, and age into the calculator to determine the Chronotropic Response Index.

Chronotropic Response Index Formula

The following formula is used to calculate the Chronotropic Response Index (CRI). 

CRI = (HRmax - HRrest) / (220 - age - HRrest)

Variables:

  • CRI is the Chronotropic Response Index
  • HRmax is the maximum heart rate during exercise (beats per minute)
  • HRrest is the resting heart rate (beats per minute) age is the age of the individual (years)

To calculate the Chronotropic Response Index, subtract the resting heart rate from the maximum heart rate during exercise. Then subtract the individual’s age from 220 and subtract the resting heart rate from this result. Finally, divide the first result by the second result.

What is a Chronotropic Response Index?

The Chronotropic Response Index (CRI) is a measure used in cardiology to assess the heart’s ability to increase its rate proportionally to the increase in physical activity or metabolic demand. It is calculated by comparing the patient’s resting heart rate to their maximum heart rate during exercise. A lower CRI indicates a less responsive or “inadequate” chronotropic response, which can be a sign of certain heart conditions or a predictor of future cardiovascular events.

How to Calculate Chronotropic Response Index?

The following steps outline how to calculate the Chronotropic Response Index (CRI).

  1. First, determine the maximum heart rate during exercise (HRmax) in beats per minute.
  2. Next, determine the resting heart rate (HRrest) in beats per minute.
  3. Next, determine the age of the individual (age) in years.
  4. Next, gather the formula from above: CRI = (HRmax – HRrest) / (220 – age – HRrest).
  5. Finally, calculate the Chronotropic Response Index (CRI).
  6. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

HRmax: maximum heart rate during exercise (beats per minute) = 180

HRrest: resting heart rate (beats per minute) = 70

age: age of the individual (years) = 35