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Rethinking the Resonance Frequency (RF) - Part 3: Slow-Paced Contraction

Updated: Mar 24

Slow-paced contraction

Slow-paced contraction (SPC) provides an alternative and unproven method for determining the resonance frequency (RF) in one or two sessions. Wrist-core-ankle contraction with crossed legs produces larger HR oscillations than wrist-ankle contraction with uncrossed legs. SPC enjoys five advantages over slow-paced breathing (SPB) protocols. First, clients can perform SPC correctly with minimal instruction. They don't have to overcome a lifetime of dysfunctional breathing habits. Second, SPC is more comfortable for chronic pain patients who often breathe faster than 20 bpm. Third, clinicians can more easily confirm compliance visually. Fourth, SPC is safer for clients whose rapid breathing compensates for an abnormal acid-base balance. SPB might endanger clients diagnosed with kidney disease. Fifth, many clients will find SPC at ~ 2 cpm easier to perform than SPB ~ 2 bpm to stimulate the vasomotor tone (VT) baroreflex.

We will discuss the equipment and displays used in SPC RF assessment, and outline RF protocols for stimulating the heart rate (HR) baroreflex and VT baroreflex.

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A Disclaimer

SPC is a validated HRV biofeedback training method (Vaschillo et al., 2002). However, SPC is an experimental RF assessment procedure that requires extensive research.

Truman State University's Center for Applied Psychophysiology was among the first laboratories to use SPC to measure the RF. We have not seen published reports comparing the SPB and SPC methods to calculate the HR baroreflex RF. We have not found reports of the 2-week test-retest reliability of SPC RF measurements. Finally, we have not discovered reports SPC training using a SPC-determined RF.

The BioSource faculty wrote this post to show clinicians and researchers how to use SPC to measure the HR baroreflex and VT baroreflex RFs. We have described the "nuts and bolts" of SPC RF assessment. We hope this post will stimulate clinic and laboratory research to evaluate this complementary RF assessment method.

We strongly caution that the SPC RF assessment method is experimental, not validated, and not an accepted part of HRV biofeedback training.

Equipment for Resonance Frequency Assessment Using Slow-Paced Contraction

You will need an electrocardiogram (ECG) for publishable research and an ECG or PPG sensor for clinical work. Your data acquisition software may require a respirometer to measure mean HR Max - HR Min, which is the difference between the fastest and slowest HR across each breathing cycle.

ECG Sensor

Place ECG sensors on the torso to avoid movement artifacts from wrist contraction. The Polar H10 is a gold standard for ambulatory ECG monitoring. The H10 is compatible with the Optimal HRV application described in this post. Graphic © Polar Electro.

Below is a three-lead Thought Technology Ltd. ECG sensor. Clients may require assistance with sensor placement. Graphic © BioSource Software.

ECG chest placement

PPG Sensor

Since wrist contraction can produce movement artifacts, you must place PPG sensors on the earlobe. The HeartMath wireless PPG sensor is an excellent option. Graphic © Institute of HeartMath.