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.