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Rethinking the Resonance Frequency (RF) - Part 2: Slow-Paced Breathing

Updated: Mar 24

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Resonance frequency (RF) assessment identifies the stimulation frequency producing the greatest amplitude heart rate oscillations in one to two sessions. We can assess the RF using slow-paced breathing (SPB) or slow-paced contraction (SPC) methods. This installment focuses on the slow-paced breathing method. We will discuss the equipment used in RF assessment and the importance of breathing assessment and training. Although we recommend using a respirometer, this does not mean you cannot measure the RF or provide effective heart rate variability (HRV) training without one. Instead, we believe that a respirometer offers assessment and training advantages.

In the third installment, we will cover RF assessment using slow-paced contraction. In the final installment, we will describe stepped and sliding protocols and their RF selection criteria. We will suggest ways to simplify RF assessment.

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Watch Dr. Inna Khazan's Heart Rate Variability: Harnessing Your Own Personal Superpower

Equipment for RF Assessment Using Slow-Paced Breathing

For publishable research, you will need an electrocardiogram (ECG) with a respirometer. We encourage using an ECG or PPG sensor with a respirometer for clinical work. Smartphone apps like Optimal HRV offer automated RF assessment using a compatible PPG sensor and their proprietary pacing display for personal training.


Clinicians use the PPG and ECG to monitor heart rate (HR) and heart rate variability (HRV). A PPG sensor detects the pulse wave as it travels through the vascular tree.

NeXus BVP sensor

Graphic © paulista/

Red blood cells

ECG sensors detect the R-spike of the QRS complex, measuring the time between successive heartbeats. A wrist placement trades ease of application for vulnerability to movement.

ECG wrist placement

Graphic © arka38/

R-spike of ECG