Slow-Paced Contraction Training with the Optimal HRV Application

Fred Shaffer
Nov 8, 2025
10 min read

Updated: Nov 10, 2025

This post explains how to deliver slow-paced contraction training, either alone or in conjunction with slow-paced breathing, using the innovative Optimal HRV application. An Optimal HRV morning reading display is shown below.

You'll learn how to use the Optimal HRV application to find your client's resonance frequency. This post explores the advantages of slow-paced contraction over slow-paced breathing and the advantages of combining them. It demonstrates HRV training using standalone slow-paced contraction and synchronized slow-paced contraction with slow-paced breathing. and provides practical guidance for implementing these techniques in clinical practice. Finally, it provides step-by-step instructions for assessing resonance frequency, training protocols, progress tracking, and integrating home practice.

Finding the Resonance Frequency

Slow-paced contraction (SPC) provides an alternative and unproven method for determining the resonance frequency in one or two sessions. The resonance frequency (RF) is the stimulation rate (breathing, muscle contraction, or synchronized muscle contraction and breathing) that produces the greatest low-frequency (LF) power and RMSSD values.

You can use the Optimal HRV application to calculate your RF for SPC or SPC + SPB. Your clients should sit with their legs supported. They will contract their wrists, core, and crossed ankles for SPC with their feet supported. They will only contract their wrists and crossed ankles in the combined condition because core contraction would prevent the diaphragm from descending.

Resonance Frequency Assessment

You can select RF Assessment at the bottom of the Optimal HRV menu. Repurpose the Optimal HRV application for SPC RF assessment. Their 14-minute RF procedure guides clients through 2-minute trials from 7.0-3.5 bpm in 0.5-bpm steps. If a person feels uncomfortable with very slow breathing, they can stop at 4 bpm. This, however, is not an issue with slow paced muscle contractions, so clients can perform the assessment from 7.0 to 3.5 cpm. The exhalations are longer than the inhalations.

Start 1.5 s before and end 1.5 s after each cycle’s peak. For SPC training, your clients may contract their wrists, core, and ankles. For combined SPC and SPB breathing training, they should only contract their wrists and ankles as they simultaneously breathe at the same rate.

Although both methods should yield the same RF, use the same stimulation method for assessment and training to ensure consistency. The Optimal HRV application calculates the RF based on LF power and MinMax (HR Max - HR Min). Although this application reports the RMSSD, it does not use it in calculating the RF.

Baseline

After choosing a contraction rate, select New Reading to calculate a pre-baseline. During the pre-baseline, instruct your client to sit quietly without SPC or SPB. Use the pre-baseline as a benchmark for HRV gains achieved during training trials. You can also record a post-baseline after training to assess pre- to post-baseline HRV changes.

Slow-Paced Contraction Training Protocols

SPC and SPC with synchronized SPB are two evidence-based training options.

SPC Versus SPB

SPC enjoys five advantages over SPB. 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 breaths per minute (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 contractions per minute (cpm) easier to perform than SPB at ~ 2 breaths per minute (bpm) to stimulate the vasomotor tone (VT) baroreflex.

SPC + SPB Versus SPC

Shaffer and colleagues (2023) studied 28 undergraduates (16 women; 12 men), ages 19-22, who could consistently breathe at 6 bpm +/- 0.7 bpm. We found that SPC + SPB yielded greater MinMax than wrist-ankle SPC alone. This is important because MinMax indexes respiratory sinus arrhythmia, which is the major parasympathetic oscillator that drives the HR baroreflex closed-loop. The combined procedure did not produce greater RMSSD or LF power in participants who could already perform SPB.

MinMax

MinMax, which was measured in beats per minute, was greater during the combined condition than SPB, F(2, 26) = 10.76, p = 0.004, partial η2 = 0.34.

SDNN

The SDNN was greater during SPB than BL, F(2, 26) = 15.67, p = 0.001, partial η2 = 0.43, and during the combined condition than BL, F(2, 26) = 16.16, p = 0.001, partial η2 = 0.44. There was no difference between the combined and SPB conditions.

Low-Frequency Power

LF power was greater during SPB than BL, F(2, 26) = 22.39, p = 0.001, partial η2 = 0.52, and during the combined condition than BL, F(2, 26) = 20.88, p = 0.001, partial η2 = 0.50. LF power was equivalent during the SPB and combined conditions.

Slow-Paced Contraction

In SPC training, instruct your client to breathe normally. SPC doesn’t use paced breathing.

They should contract their wrists, core, and ankles to maximize HRV increases.

Encourage Effortlessness

Borrowing from Dr. Erik Peper, encourage effortless contraction to ensure a smooth rhythm and minimize fatigue. Your clients should use about 25% of maximum effort. They should feel as if their wrists and ankles are contracting themselves.

Following the pre-baseline, go to the Biofeedback menu option at the bottom of the screen. Select Biofeedback Training from the menu at the top.

Select the 6.0 bpm option or your client’s RF.

Set the timer for 3 min and enable Track HRV. Select Start Training. When you have finished a 3-min trial, Optimal HRV will calculate LF power, the RMSSD, MinMax, and the SDNN.

The video below shows a SPC trial guided by the Optimal HRV application.

Coach and start a new trial. After six HRV training trials, repeat the 3-min resting baseline.

Slow-Paced Contraction and Slow-Paced Breathing

In SPC+SPB training, instruct your client to synchronize muscle contraction and breathing using the pacing display. They should contract their wrists and ankles while gently inhaling through their nostrils 1.5 s before each cycle's peak. They should relax their wrists and ankles while gently exhaling through pursed lips 1.5 s after each cycle’s peak. The pursed lips provide greater respiratory feedback and control over exhalation.

Synchronizing contraction and breathing maximizes the combined effects of these oscillators. Your clients will achieve the greatest HRV increases when wrist-ankle contraction and inhalation are simultaneous. This is analogous to when all singers articulate their attacks and releases in precise unison.

Encourage Effortlessness

Encourage effortless contraction and breathing to ensure a smooth rhythm, minimize fatigue, and prevent vagal withdrawal. Rather than forcing contractions through conscious effort, clients learn to allow their body to contract and breathe with minimal exertion, using approximately 25% of their maximum strength. This gentle approach creates the smooth, rhythmic oscillations necessary for optimal HRV enhancement while preventing the fatigue and tension that can disrupt autonomic balance.

Your clients should use about 25% of maximum effort. They should feel as if their wrists and ankles are contracting themselves and that their body is breathing itself. Following the pre-baseline, go to the Biofeedback menu option at the bottom of the screen. Select Biofeedback Training from the menu at the top.

Select the 6.0 bpm option or your client’s RF.

Set the timer for 3 min and enable Track HRV. Select Start Training. When you have finished a 3-min trial, Optimal HRV will calculate LF power, the RMSSD, MinMax, and the SDNN.

The video below shows a SPC+SPB trial guided by the Optimal HRV application.

Session Overview

Understanding session structure and metrics helps both practitioners and clients track progress effectively. Each training session follows a predictable pattern: pre-baseline assessment, multiple training trials with real-time feedback, and post-baseline measurement. The Optimal HRV application automatically calculates key metrics, including low-frequency power, RMSSD, and SDNN, providing objective markers of autonomic function that guide protocol adjustments and demonstrate improvement over time.

Progress and Difficulty Indicators

Monitoring client progress requires attention to both quantitative metrics and qualitative observations. The application's built-in tracking features display session-by-session changes in HRV parameters, while practitioners assess subjective indicators like perceived effort, rhythm consistency, and fatigue levels. These combined measures help determine when to advance training difficulty, adjust contraction rates, or modify session duration to maintain the optimal level of challenge for continued improvement.

Progressive Home Practice Schedule

Successful HRV training extends beyond the clinical setting through structured home practice that builds gradually over weeks. Beginning with brief 5-minute sessions, clients progressively increase duration and frequency as their capacity develops. This systematic approach ensures sustainable skill development while preventing overwhelm, allowing the nervous system to adapt gradually to enhanced autonomic regulation.

Integrate Mindfulness Into Home Practice

Combining mindfulness techniques with HRV training amplifies therapeutic benefits by enhancing present-moment awareness and reducing cognitive interference. Clients learn to observe their internal sensations during contractions, notice the quality of their breathing, and maintain gentle attention on the rhythm of practice. This mindful approach transforms mechanical exercises into opportunities for deeper self-regulation, supporting the transfer of HRV skills to emotionally challenging situations.

Key Takeaways

SPC offers a simpler alternative: Clients can perform slow-paced contractions correctly with minimal instruction, avoiding the challenges of overcoming dysfunctional breathing patterns.
The resonance frequency principle remains constant: Whether using breathing or muscle contractions, the goal is finding the stimulation rate that produces the greatest low-frequency power and RMSSD values.
Effortlessness is essential: Using only 25% of maximum effort ensures smooth rhythm, minimizes fatigue, and prevents vagal withdrawal during training.
Combined protocols maximize benefits: Synchronizing muscle contractions with breathing (SPC+SPB) yields greater improvements in MinMax than either method alone.
Progressive home practice ensures transfer: Starting with brief twice-daily sessions and gradually increasing duration helps clients integrate HRV skills into daily life.

Appreciation

The Truman Center for Applied Psychophysiology research staff made this post possible. A special thanks to my amazing Lab Managers, Isaac Compton and Emma Suchsland, who teach and supervise this dedicated team of 33 undergraduates. Isaac Compton modeled our wrists-core-ankles SPC technique.

Glossary

baroreflex: an autonomic reflex loop whose oscillations (e.g., vasomotor tone) can be stimulated by slow-paced breathing or slow-paced contraction to augment heart rate variability.

beats per minute (bpm): a pacing rate unit used for breathing or combined contraction-breathing trials (e.g., 7.0–4.0 bpm during resonance frequency assessment).

contractions per minute (cpm): a pacing rate unit for slow-paced muscle contraction (e.g., ~2 cpm).

diaphragm (descent): the inferior movement of the diaphragm during inhalation; continuous core contraction is avoided in combined SPC+SPB because it would prevent this descent.

heart rate maximum (HR Max): the peak heart rate within a breathing or contraction cycle, used in computing the MinMax metric.

heart rate minimum (HR Min): the trough heart rate within a breathing or contraction cycle, used in computing the MinMax metric.

heart rate variability (HRV): the beat-to-beat variation in heart period used as the primary outcome metric during training and assessment.

low-frequency (LF) power: spectral power in the low-frequency band; in this protocol, the resonance frequency is defined as the stimulation rate producing the greatest LF power and RMSSD.

Min: the lowest value of a given HRV statistic during a condition or trial (used in the document when comparing SPC versus SPC+SPB outcomes).

mindfulness: a metacognitive state characterized by sustained, nonjudgmental awareness of present-moment experience—internal and external—without reactive identification or avoidance. In psychophysiological training, mindfulness is operationalized as the deliberate observation of sensations, thoughts, and autonomic shifts (e.g., respiration, heart rate) while maintaining attentional stability. It enhances interoceptive accuracy and self-regulation by reducing habitual cognitive elaboration and promoting parasympathetic engagement.

MinMax (HR Max − HR Min): a time-domain amplitude index reported by the app but not used to determine resonance frequency.

Optimal HRV application: the mobile application used to pace trials and compute metrics such as LF power, RMSSD, MinMax, and SDNN; it also delivers a 14-minute resonance-frequency assessment.

oscillator (physiological): a rhythmic biological driver (e.g., breathing, muscle contraction); synchronizing oscillators (contraction with inhalation) maximizes HRV effects.

pacing display: the on-screen guide indicating cycle peaks for timing inhalation/exhalation and contraction/relaxation during SPC+SPB. post-baseline: a quiet resting period recorded after training during which clients breathe normally and do not contract their wrists, core, or ankles. It is used as a benchmark to evaluate HRV gains since the pre-baseline.

pre-baseline: a quiet resting period recorded before training during which clients breathe normally and do not contract their wrists, core, or ankles. It is used as a benchmark to evaluate HRV gains during subsequent trials and longitudinally across training sessions.

pursed-lips exhalation: a gentle exhalation through partially closed lips that increases expiratory resistance, providing stronger respiratory feedback and control.

resonance frequency (RF): the stimulation rate (breathing, contraction, or synchronized contraction plus breathing) that yields the greatest LF power and RMSSD.

resonance frequency assessment: a structured series of seven 2-minute trials (7.0 to 4.0 bpm in 0.5-bpm steps) used to estimate RF, with inhalations shorter than exhalations.

RMSSD (root mean square of successive differences): a time-domain HRV index emphasized, along with LF power, for identifying resonance frequency.

SDNN (standard deviation of normal-to-normal intervals): a global time-domain HRV metric computed after each training trial.

self-compassion training: a structured practice cultivating kindness toward oneself in moments of difficulty or perceived inadequacy. It involves three primary elements: (1) self-kindness rather than self-criticism, (2) recognition of common humanity rather than isolation, and (3) mindful awareness rather than over-identification with distress.

slow-paced breathing (SPB): paced respiration (typically around ~6 bpm) used as a stimulus to engage baroreflex mechanisms and increase HRV.

slow-paced contraction (SPC): rhythmic, low-effort contraction of wrists, core, and ankles at a prescribed rate, employed as an alternative stimulus to SPB to increase HRV.

SPC+SPB (synchronized): a combined procedure in which wrist-ankle contraction coincides with inhalation and relaxation coincides with exhalation to amplify HRV effects.

vagal withdrawal: a reduction in parasympathetic (vagal) influence; the document advises effortless contraction to minimize fatigue and prevent vagal withdrawal.

vasomotor tone (VT): vascular smooth-muscle constriction–dilation activity implicated in the baroreflex; very slow SPC (~2 cpm) is suggested as a way to stimulate VT.

References

Meehan, Z. M., & Shaffer, F. (2023). Adding core muscle contraction to wrist-ankle rhythmical skeletal muscle tension increases respiratory sinus arrhythmia and low-frequency power. Applied Psychophysiology and Biofeedback, 48(1), 127–134. https://doi.org/10.1007/s10484-022-09568-w

Shaffer, F., & Ginsberg, J. P. (2017). An overview of heart rate variability metrics and norms. Frontiers in Public Health. https://doi.org/10.3389/fpubh.2017.00258

Shaffer, F., Moss, D., & Meehan, Z. M. (2022). Rhythmic skeletal muscle tension increases heart rate variability at 1 and 6 contractions per minute. Appl Psychophysiol Biofeedback. https://doi.org/10.1007/s10484-022-09541-7

Shaffer, F., Compton, I., Wills, C., & Suchsland, E. (2023). Does combining slow-paced breathing and slow-paced muscle contraction increase HRV? [Oral paper presentation]. Presented at the 53rd Association for Applied Psychophysiology and Biofeedback Annual Meeting, Orlando, Florida.

Vaschillo, E., Lehrer, P., Rishe, N., & Konstantinov, M. (2002). Heart rate variability biofeedback as a method for assessing baroreflex function: A preliminary study of resonance in the cardiovascular system. Applied Psychophysiology and Biofeedback, 27, 1-27. https://doi.org/10.1023/A:1014587304314

Vaschillo, E. G., Vaschillo, B., Pandina, R. J., & Bates, M. E. (2011). Resonances in the cardiovascular system caused by rhythmical muscle tension. Psychophysiology, 48, 927–936. https://doi.org/10.1111/j.1469-8986.2010.01156.x

About the Author

Fred Shaffer earned his PhD in Psychology from Oklahoma State University. He earned BCIA certifications in Biofeedback and HRV Biofeedback. Fred is an Allen Fellow and Professor of Psychology at Truman State University, where has has taught for 50 years. He is a Biological Psychologist who consults and lectures in heart rate variability biofeedback, Physiological Psychology, and Psychopharmacology. Fred helped to edit Evidence-Based Practice in Biofeedback and Neurofeedback (3rd and 4th eds.) and helped to maintain BCIA's certification programs.