Slow-paced contraction (SPC) increases heart rate variability (HRV) as effectively as slow-paced breathing (SPB). Although the excellent Optimal HRV application was designed for SPB, it can easily be repurposed in the clinic and at home for SPC training.
The Case for Slow-Paced Contraction
SPC provides a "Plan B" when clients find SPB difficult or medically contraindicated. Real Genius episode on WEBTOON drawn by Dani S@unclebelang on Fiverr.com.
SPB Can be Challenging
SPB requires substantial practice and may not be feasible for everyone (Critchley, 2015; Mozer et al., 2014). For example, although Strauss-Blasche et al. (2000) instructed participants to breathe at 6 bpm, they actually breathed 9.6 ± 3.1 and 10.0 ± 3.1 bpm. SPB can also be challenging for clients who breathe dysfunctionally (e.g., overbreathing). Graphic © Silvia Bukovac/Shutterstock.com.
Disorders like COPD that affect respiration may raise rates to 18-28 bpm (Fried, 1987; Fried & Grimaldi, 1993). Graphic © urbans/Shutterstock.com.
Sustained pain increased respiration rates from 13.2 to 17.7 bpm (Kato, Kowalski, & Stohler, 2001). These patients may be unable to slow their breathing to 4.5 to 6.5 bpm. Graphic © Triff/Shutterstock.com.
SPB May be Medically Contraindicated
SPB may be medically contraindicated when breathing could be hazardous if your client suffers from diabetes (Kitabchi et al., 2009) or kidney disease (Kim, 2021) that produce metabolic acidosis (i.e., excess acid in the body fluid). Graphic © RomarioIen/Shutterstock.com.
Common respiratory acidosis causes include chronic obstructive pulmonary disease (COPD), asthma, pneumonia, and neuromuscular disorders that affect breathing muscles. Graphic © Andrey_Popov/Shutterstock.com.
Patients may breathe rapidly to protect acid-base balance in medical disorders that cause a decrease in blood pH, leading to acidosis. Rapid breathing helps expel carbon dioxide (CO2) from the body, increasing the pH and counter acidosis. Real Genius episode on WEBTOON drawn by Dani S@unclebelang on Fiverr.com.
Slow-Paced Contraction Description
In SPC, clients sit upright in a chair with their feet supported by another chair. Adults
briefly contract skeletal muscles (wrist, core, and ankles) for 3 s at the same 4.5 to 6.5 cpm rates they would use in SPB. They breathe normally. Guided by a breathing pacing display and verbal prompts, clients start moderate contraction 1.5 s before the display's peak and continue for 1.5 s after.
Slow-Paced Contraction Using Optimal HRV
Instruct your client to place an ECG sensor on their torso to avoid movement artifacts from forearm contraction. The Polar H10 is a gold standard for ambulatory ECG monitoring.
Clients sit upright in a chair with their feet supported by another chair and ankles crossed. Although the original Vaschillo protocol only contracted wrists and ankles with legs uncrossed, we have observed greater RSA using wrist, core, and crossed-ankle contraction.
Optimal HRV
Optimal HRV is an application designed to monitor and analyze heart rate variability (HRV) to optimize health and performance. The app provides insights into an individual's autonomic nervous system function, stress levels, and recovery status. Key features include:
HRV Tracking: Continuous or periodic measurement of HRV using compatible devices.
Data Analysis: Detailed analysis and visualization of HRV metrics to identify trends and patterns.
Personalized Insights: Custom recommendations based on HRV data to improve overall health, manage stress, and enhance athletic performance.
Integration: Compatibility with various fitness trackers and health platforms for comprehensive health monitoring.
User-Friendly Interface: Intuitive design for easy navigation and understanding of complex HRV data.
SPC Using Optimal HRV
You can measure your client’s resonance frequency (RF) or use 6 cpm. Select RF
Assessment at the bottom of the Optimal HRV menu.
Prebaseline
Select New Reading to calculate a pre-baseline after choosing a contraction rate. Instruct your client to breathe normally and sit quietly.
SPC Training
Following the pre-baseline, go to the Biofeedback menu option at the bottom of the screen. Select Biofeedback Training at the top menu.
Select the 6.0 bpm option or your client’s RF.
Set the timer for 3 min and enable Track HRV. Select Start Training.
SPC doesn’t use paced breathing.
Instead of paced breathing, contract the wrists-core-ankles with legs crossed for 3 s. Start 1.5 s before and end 1.5 s after each cycle’s peak. Borrowing from Dr. Erik Peper, encourage effortless contraction to ensure a smooth rhythm and minimize fatigue. Your clients should use about 25% of their maximum effort. They should feel like their wrists, core, and ankles are contracting themselves. Contraction should be effortless to avoid triggering vagal withdrawal in which parasympathetic control of the large internal organs disengages. When your training protocol is stressful, HRV and skin temperature may decline, and skin conductance may rise.
When you have finished a 3-min trial, Optimal HRV will calculate LF power, the RMSSD, HR Max – HR Min, and the SDNN.
Coach and start a new trial. After six HRV training trials, repeat the 3-min resting baseline.
Training Overview
Progressively increase training time. Optimal HRV recommends that your client choose a time that works best for them and progress from shorter to longer practice sessions. Week 1, 5 min per day. Week 2, 10 min per day. Week 3, 15 min per day.
Week 4+, 20 min per day.
Practice can incorporate Mindfulness Training and Self-Compassion Training from the Mindfulness and Biofeedback menu.
The Scientific Evidence
Lehrer et al. (2009) studied the effects of wrist and ankle contractions. They reported that 6-cpm wrist-ankle SPC increased oscillations in BP, HR, and pulse transit time (PTT; the time for a pulse wave to travel between two arterial sites).
Vaschillo et al. (2011) compared 6-cpm SPC with 6-bpm SPB. SPC only produced high-amplitude oscillations in BP, HR, and tidal volume (TV; the amount of air exhaled during a breath) at 0.1 Hz. HR and TV oscillations at 0.1 Hz were 4 to 6 times greater than those at 0.05 or 0.2 Hz, irrespective of the breathing rate.
Shaffer, Moss, and Meehan (2022) reported that 1- and 6-cpm SPC increased several HRV metrics (e.g., the RMSSD, SDNN, and low-frequency power) to a greater degree than SPC at 12 cpm. There were no differences between the 1- and 6 -cpm conditions.
Meehan and Shaffer (2022) compared 6-cpm wrist-ankle and wrist-core-ankle SPC with a resting baseline. The two SPC conditions produced greater HR Max-HR Min and LF power than the control condition. Wrist-core-ankle SPC yielded greater HR Max-HR Min than wrist-ankle SPC.
Meehan and Shaffer (2024) compared 6-cpm wrist-ankle SPC, 6-cpm wrist-ankle SPC with 6-bpm SPB, and a resting baseline. The two experimental conditions produced greater HR Max-HR Min, RMSSD, SDNN, and LF values than the control condition. Combining SPC with SPB yielded greater HR Max-HR Min than wrist-ankle SPC alone.
Synthesis
Six-cpm wrist-ankle and wrist-core-ankle SPC produce comparable HRV increases as 6-bpm SPB. Wrist-core-ankle SPC produced greater HR Max-HR Min than wrist-ankle SPC. You can combine 6-cpm wrist-ankle SPC with 6-bpm SPB, and this more challenging procedure increases HR Max-HR Min more than wrist-ankle SPC alone.
SPC's Broader Implications
SPC is a "Plan B" for HRV biofeedback training. Because it does not rely on respiratory processes—only the rhythmic recruitment of muscle groups—it is a helpful alternative for HRV biofeedback training for those who would otherwise find traditional paced breathing exercises uncomfortable or harmful.
Appreciation
The Truman Center for Applied Psychophysiology research staff made this post possible. A special thanks to my amazing Lab Managers, Gabriel Durkee and Melody Zakarian, who teach and supervise this dedicated team of 26 undergraduates. Isaac Compton modeled our wrists-core-ankles SPC technique.
Glossary
baroreflex: baroreceptor reflex that provides negative feedback control of BP. Elevated BP activates the baroreflex to lower BP, and low BP suppresses the baroreflex to raise BP.
HR Max – HR Min: an HRV index that calculates the average difference between the highest and lowest HRs during each respiratory cycle.
metabolic acidosis: a disorder marked by a decrease in blood pH and bicarbonate (HCO₃⁻) levels due to the accumulation of acids or loss of bicarbonate. It can result from conditions such as diabetic ketoacidosis, renal failure, or severe diarrhea.
peak frequency: the HRV frequency with the greatest power.
prebaseline: physiological measurement without breathing or muscle contraction instructions or feedback.
pulse transit time (PT): the time for a pulse wave to travel between two arterial sites.
resonance frequency: the frequency at which a system, like the cardiovascular system, can be activated or stimulated.
respiratory acidosis: a condition characterized by an increase in arterial carbon dioxide tension (PaCO₂) due to inadequate ventilation, leading to a decrease in blood pH. Common causes include chronic obstructive pulmonary disease (COPD), respiratory muscle weakness, and central nervous system depression.
RMSSD: the square root of the mean squared difference of adjacent NN intervals in milliseconds.
SDNN: the standard deviation of the normal (NN) sinus-initiated IBI measured in milliseconds.
slow-paced contraction (SPC): wrist-ankle or wrist-core-ankle contraction in the adult 4.5-6.5 cpm range.
slow-paced breathing (SPB): breathing in the adult 4.5-6.5 bpm range.
References
Critchley, H., Nicotra, A., Chiesa, P., Nagai, Y., Gray, M., Minati, L., & Bernardi, L. (2015). Slow breathing and hypoxic challenge: Cardiorespiratory consequences and their central neural substrates. PLoS ONE, 10. https://consensus.app/papers/breathing-hypoxic-challenge-cardiorespiratory-critchley/58e85f10d1a1512694b979b848b25604/?utm_source=chatgpt
Fried, R. (1987). The hyperventilation syndrome: Research and clinical treatment. John Hopkins University Press.
Fried, R., & Grimaldi, J. (1993). The psychology and physiology of breathing. Springer.
Hansen, A. L., Johnsen, B. H., & Thayer, J. F. (2009). Relationship between heart rate variability and cognitive function during threat of shock. Anxiety, Stress, and Coping, 22(1), 77–89. https://doi.org/10.1080/10615800802272251
Kato, Y., Kowalski, C. J., & Stohler, C. S. (2001). Habituation of the early pain-specific respiratory response in sustained pain. Pain, 91(1-2), 57–63. https://doi.org/10.1016/s0304-3959(00)00419-x
Kim, H. J. (2021). Metabolic acidosis in chronic kidney disease: Pathogenesis, clinical consequences, and treatment. Electrolyte & Blood Pressure: E & BP, 19(2), 29–37. https://doi.org/10.5049/EBP.2021.19.2.29
Kitabchi, A. E., Umpierrez, G. E., Miles, J. M., & Fisher, J. N. (2009). Hyperglycemic crises in adult patients with diabetes. Diabetes Care, 32(7), 1335–1343. https://doi.org/10.2337/dc09-9032
Lehrer, P. (2022). My life in HRV biofeedback research. Applied Psychophysiology and Biofeedback, 1-10. https://doi.org/10.1007/s10484-022-09535-5
Lehrer, P., Kaur, K., Sharma, A., Shah, K., Huseby, R., Bhavsar, J., Sgobba, P., & Zhang, Y. (2020). Heart rate variability biofeedback improves emotional and physical health and performance: A systematic review and meta-analysis. Applied Psychophysiology and Biofeedback, 45, 109-129. https://doi.org/10.1007/s10484-020-09466-z
Meehan, Z. M., & Shaffer, F. (2024). Adding core muscle contraction to wrist-ankle rhythmical skeletal muscle tension increases respiratory sinus arrhythmia and low-frequency power. Applied Psychophysiology and Biofeedback.
Mozer, M. T., Fadel, P., Johnson, C. M., Wallin, B., Charkoudian, N., Drobish, J. N., & Wehrwein, E. (2014). Acute slow‐paced breathing increases periods of sympathetic nervous system quiescence (1170.12). The FASEB Journal, 28(1), 1170.12. https://consensus.app/papers/acute-slow‐paced-breathing-increases-periods-system-mozer/4e8ff43b4a0f5126b41336c53c38d7bf/?utm_source=chatgpt
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
Strauss-Blasche, McLeod, D. R., Klammer, N., & Marktl, W. (2000). Relative timing of inspiration and expiration affects respiratory sinus arrhythmia. Clinical and Experimental Pharmacology & Physiology, 27, 601–606. https://doi.
/10.1046/j.1440-1681.2000.03306.x.
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
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