Slow-Paced Contraction Increases HRV

Introduction to Slow-Paced Contraction

Slow-paced contraction (SPC) offers an alternative to slow-paced breathing (SPB), which is sometimes challenging (e.g., chronic pain) or medically contraindicated (e.g., kidney disease). SPC may be helpful for clients who breathe dysfunctionally or who cannot slow their breathing to the adult resonance frequency range (4.5 to 6.5 bpm).

Description In slow-paced contraction (SPC) exercises, clients briefly contract and relax skeletal muscles (wrist and ankles or wrist, core, and ankles) at the same 4.5 to 6.5 cpm rates as they breathe normally. For example, for 6 cpm, a display would prompt them to contract their muscles for 4 and relax for 6 s. Contraction force should be moderate, but not maximal, to ensure a smooth rhythm and minimize fatigue.

Choose an ECG sensor using a chest or upper torso placement, shown respectively.

Alternately, select a PPG sensor attached to an earlobe. Graphic courtesy of the Institute of HeartMath.

While reclining with feet supported by a chair, your clients can rhythmically contract their hands, core, and feet for 3 seconds at their resonance frequency (i.e., optimal stimulation rate) to increase heart rate variability (Vaschillo et al., 2011). 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.

Mechanism Like slow-paced breathing (SPB), SPC amplifies heart rate oscillations and stimulates the baroreceptor reflex to increase heart rate variability.

SPC increases blood pressure, heart rate, and vasomotor tone oscillations. These effects are due exclusively to increased vagus nerve firing (Lehrer, 2022; Vaschillo et al., 2002).

Maximum-Minimum heart rate for each breath indexes respiratory sinus arrhythmia (RSA). The peak frequency is the HRV frequency with the greatest power. In the screen captures below, SPC stimulated the baroreceptor reflex at the intended frequency (0.2 Hz for 12 cpm and 0.1 Hz for 6 cpm) for the same participant. Below is a BioGraph Infiniti display of 12-cpm SPC. At the top right, note that the Maximum - Minimum heart rate for each breath is 8 bpm. On the left, the peak frequency is 0.2 Hz. Click on the next two screen captures to enlarge them.

Next, is a 6-cpm SPC display. The Maximum - Minimum heart rate for each breath is 30 bpm. On the left, the peak frequency is 0.1 Hz. Without breathing instructions, the participant slowed to 6 bpm, amplifying RSA.

Research Shaffer, Moss, and Meehan (2022) reported that SPC at 1 and 6 contractions per minute (cpm) increased five time-domain metrics (HR Max – HR Min, RMSSD, SDNN, TI, and TINN), one frequency-domain metric (LF power), and three non-linear metrics (D2, SD1, SD2) to a greater degree than SPC at 12 cpm. There were no differences between the 1 and 6 cpm conditions. Meehan and Shaffer (in press) compared 6-cpm wrist-ankle SPC with 6 -cpm wrist-core-ankle SPC. Both conditions produced greater HR, HR Max-HR Min, and LF power than the control condition. The wrist-core-ankle method yielded greater HR and HR Max-HR Min than wrist-ankle SPC.

Note. Descriptive statistics represent the results of untransformed, raw data. Error bars represent the 95% confidence interval around the mean.

Note. Descriptive statistics represent the results of untransformed, raw data. Error bars represent the 95% confidence interval around the mean.

An Intriguing Question

What if we combined 6-cpm SPC with 6-bpm SPB? Could two oscillators produce greater RSA than one? Preliminary data from the Truman Center for Applied Psychophysiology suggest this could be the case. RSA The first screen shows 6-cpm SPC while the participant breathed at 13.02 bpm. HR Max - HR Min was 13 bpm. The peak frequency (shown in red) was the target 0.1 Hz.

The second screen shows 6-cpm SPC with 6-bpm SPB. HR Max - HR Min was 36 bpm. The peak frequency (shown in red) was the target 0.1 Hz.

Time-Domain Measurements The first Kubios table shows 6-cpm SPC. RMSSD was 55 ms.

The second table shows 6-cpm SPC with 6-bpm SPB. RMSSD was 88 ms.

Frequency-Domain Measurements The first table shows 6-cpm SPC. Low-frequency power (ms2/Hz) using the FFT method was 5046. The participant breathed normally at 7.8 bpm.

The second table shows 6-cpm SPC with 6-bpm SPB. Low-frequency power (ms2/Hz) using the FFT method was 12277. The participant breathed at the target of 6 bpm.

Pilot Summary These pilot data suggest that two oscillators, 6-cpm SPC and 6-bpm SPB, can synergistically increase RSA and HRV time- and frequency-domain measurements. Confirmation awaits a planned Truman Center randomized controlled trial since pilot data might be outliers.

SPC's Broader Implications SPC has practical implications for HRV biofeedback training and mental health. Because SPC does not rely on respiratory processes—only the rhythmic recruitment of muscle groups—it may represent a helpful alternative for HRV biofeedback training for those who otherwise would find traditional paced-breathing exercises to be uncomfortable or harmful. For clients who can learn both SPC and SPB, combining these oscillators may produce greater RSA and vagal tone than one method alone. This protocol requires experimental confirmation. There is convincing evidence of HRV biofeedback training benefits in psychiatric illnesses. Lehrer and colleagues (2020) reported that HRV biofeedback produces large improvements in anxiety and depression. HRV biofeedback training can also benefit patient stress. Teaching individuals to increase HRV under stress conditions is correlated with improved cognitive performance under such conditions (Hansen et al., 2009). A meta-analysis (Goessl et al., 2017) found that HRV biofeedback yielded large reductions in self-reported anxiety and stress.

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 18 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. D2: correlation dimension estimates the minimum number of variables required to construct a system dynamics model. HR Max – HR Min: an HRV index that calculates the average difference between the highest and lowest HRs during each respiratory cycle. low-frequency (LF) band: a HRV frequency range of 0.04-0.15 Hz that may represent the influence of PNS and baroreflex activity when breathing or contracting muscles between 4.5-6.5 times a minute. peak frequency: the HRV frequency with the greatest power. resonance frequency: the frequency at which a system, like the cardiovascular system, can be activated or stimulated. respiratory sinus arrhythmia (RSA): the respiration-driven heart rhythm that contributes to the high frequency (HF) component of heart rate variability. Inhalation inhibits vagal nerve slowing of the heart (increasing HR), while exhalation restores vagal slowing (decreasing HR). RMSSD: the square root of the mean squared difference of adjacent NN intervals in milliseconds. SD1: the standard deviation of the distance of each point from the y = x-axis that measures short-term HRV.

SD2: the standard deviation of each point from the y = x + average RR interval that measures short- and long-term HRV. SDNN: the standard deviation of the normal (NN) sinus-initiated IBI measured in milliseconds. triangular index (TI): a geometric measure based on 24-hour recordings, which calculates the integral of the RR interval histogram's density divided by its height. triangular interpolation of the NN interval histogram (TINN): the baseline width of a histogram displaying NN intervals.

Summary

Where slow-paced breathing is challenging (e.g., chronic pain) or medically contraindicated (e.g., kidney disease), wrist-core-ankle SPC with legs crossed may stimulate the baroreflex more powerfully than wrist-ankle SPC with legs uncrossed. Preliminary data suggest that two oscillators, 6-cpm SPC and 6-bpm SPB, can synergistically increase RSA and HRV time- and frequency-domain measurements.

References Goessl, V. C., Curtiss, J. E., & Hofmann, S. G. (2017). The effect of heart rate variability biofeedback training on stress and anxiety: A meta-analysis. Psychological medicine, 47(15), 2578–2586. https://doi.org/10.1017/S0033291717001003 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 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. (in press). Adding core muscle contraction to wrist-ankle rhythmical skeletal muscle tension increases respiratory sinus arrhythmia and low-frequency power. Applied Psychophysiology and Biofeedback. 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 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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