The chronotropic relates a patient's reserves of heart rate to metabolic capacity during exercise testing. It is calculated based on patient-specific parameters. It is independent of a patient's fitness level and the exercise testing method used.


percent of heart rate reserved used =

= 100% * ((heart rate during stage) – (heart rate at rest)) / ((peak heart rate) – (heart rate at rest))


percent of metabolic reserve used =

= 100% * ((METs for stage) – (METs at rest)) / ((METs at peak) – (METs at rest))



• peak heart rate = (220 – (age in years))

• Usually METs are estimated based on the protocol and stage used; they are not directly measured.

• If the patient is evaluated during peak exercise, then the metabolic reserve portion equals 1.


chronotropic index =

= (heart rate reserve used) / (metabolic reserve used)



• The normal chronotropic index is 1.0 (95% CI 0.8 to 1.3).

• A chronotropic index < 0.8 indicates a low chronotropic index


Factors not affecting the chronotropic index (Lauer, 1999, page 525):

(1) physical fitness

(2) exercise time

(3) level of functional capacity

(4) exercise protocol

(5) stage of exercise protocol


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