Strength Training for Your Nervous System—Yes, Really—Might Be the Missing Piece in Your Running Recovery

I take a slow, deep, belly inhale for five, following a little dot that’s climbing up a line graph on the screen in front of me, then breathe out for seven as the dot rolls back down. A strap around my waist measures my exhales, while a blood-pulse oximeter on my finger calculates my blood oxygen and pulse rate. Three colorful bars next to the moving dot track my stress levels in red, my parasympathetic nervous system in green, and how hard my nervous system is working in blue.I’m exercising resonance frequency breathing, which, unlike regular breathing, uses an individualized, calibrated frequency so I can mechanically increase my heart rate variability. Why do I want to do that? Because higher HRV, relative to my own baseline, helps me activate my parasympathetic nervous system, which controls my body’s ability to relax, rest, and digest, leading to a slower heart rate, lower blood pressure, and a restored state of relaxation.Administering the biofeedback session is Erin Ayala, PhD, a licensed psychologist, certified mental performance consultant, and the founder of Skadi Sport Psychology based in Minneapolis, Minnesota. I’m sitting underneath her tent at FeistyFest, a three-day movement and educational festival for women held in September in Breinigsville, Pennsylvania. “In the past 30-ish seconds, you can see how much the blue and the red dropped, and the green increased,” Ayala says to me. Translation: My nervous system is feeling very happy. I’ll be very grateful later that I audio-recorded the session, because I’m so relaxed that I’m tuning Ayala’s words out—I’m in the zone.This type of breathwork is “a straight shot to the nervous system, where it starts to hang out with your changing heart rate at the sweet spot, and that increases your HRV,” Ayala said during her HRV session earlier that weekend. Essentially, she added, resonance frequency breathing is “a strength-training session for your nervous system.”You heard right: strength-training session for your nervous system. Several small studies have shown that resonance frequency breathing has a physiological impact on HRV and blood pressure regulation—and, in turn, can be linked to a positive effect on performance. By practicing resonance frequency breathing, you’re teaching your parasympathetic nervous system to kick in, and by its activation, you’re supporting your recovery and regulation—both very important to runners. A small 2020 study published in the Journal of Human Kinetics also found a promising improvement in 5K performance of track athletes after heart-rate-variability biofeedback training.Let’s get into the what, why, and how.What Is HRVYour heart is not a metronome; it doesn’t have a perfectly steady pace. Heart rate variability measures the micro-fluctuations (in milliseconds) in the time intervals between adjacent beats, and it’s a good indicator of how well your nervous system balances stress and recovery. The normal HRV range for healthy adults is between 19 and 75 milliseconds, and our individual baselines vary greatly based on age, genetics, fitness level, and daily habits (the genetic part accounts for 50 to 60 percent of the difference). Generally speaking, the higher the number within your baseline, the better; the lower it is, the more likely you’re stressed, fatigued, dealing with poor sleep, or not recovering the way you should.Your HRV drops when your sympathetic nervous system (fight or flight) activates and overrides your parasympathetic nervous system. That serves you well in the short term, as it’s essential in preparing your body to react quickly and safely to danger or intense physical demands. But the system’s prolonged activity has a negative impact—it keeps flooding the body with stress hormones, strains (and can eventually damage) the heart, and can harm the body in other ways.You want to be able to reactivate the parasympathetic nervous system, and you can support that activation by getting your HRV back up. “The goal is to be able to get back on track quicker,” Ayala says. “We’ll still spiral, we’re still human, we still have difficult thoughts and feelings and situations and emotions, but we’re gonna feel more like it’s okay. We’ll move on. We’ll get through it.”In many ways, HRV is influenced by lifestyle habits (a sure way to tank it is, for example, by drinking alcohol). Some ways to help increase it are good sleep hygiene, exercise, staying hydrated, and decreasing stress. All of these are simple in theory, but we can only control so much how well we sleep or how stressful our days are.What we can control, though, is our breathing.More Than Just a Breathing ExerciseWhen you feel stressed and have the need to take a deep breath, you’re definitely onto something. How you take these breaths, however, matters. “‘Take a deep breath’ usually turns into a big gulp of air with your shoulders up by your ears—a single breath like that doesn’t calm much, because the most important part of this type of breathwork is the slow pace,” Ayala says.For the resonance frequency breathing to work, the breath needs to be low and slow. The best way to think about it is to pretend you’re blowing one big bubble, Ayala says. Breathing too hard, deep, or fast blows off CO2, constricting blood vessels in the brain, leading to less oxygen reaching brain tissue—which is where the lightheadedness, tingling, and racing heart come from, she adds. “Forcing it can push you toward more arousal, the opposite of what you’re after.”How many breaths you take per minute also matters. Resonance frequency breathing is most effective when an individual breathes at their unique, personalized rate. “We’re all gonna have a bit of a different number based on our unique physiology,” Ayala says. “Our happy spot typically ranges from five to six breaths per minute—you inhale to the count of four, exhale to the count of six, so that's a 10-second breath.” (Similarly, a 5-second inhale and a 7-second exhale would bring the total of breaths to five per minute.) The exact inhale-exhale ratio doesn’t matter; the resonance effect comes from the total length of each breath, but a longer exhale generally helps people feel more relaxed and less stressed—as long as we breathe slowly, Ayala adds.How to Determine Your Resonance Frequency BreathingIn an ideal world, you would do a resonance frequency assessment with an expert, where you test various lengths of inhales from 4 to 7.5 seconds, with corresponding exhales, and the administrator would evaluate the frequency at which your HRV is highest and your body happiest.While not as precise, there are apps that can help—Ayala recommended Optimal HRV and Elite HRV. If you go that route, she recommends following these tips:Use a chest strap rather than a wrist sensor because it’s more accurate.Follow a pacer for two to three minutes at each rate: 6.5, 6, 5.5, 5, and 4.5 breaths per minute.Pick the rate that gives the biggest, smoothest heart-rate wave. If you can measure HRV, pick the rate that gives you the highest HRV.Repeat on a few different days and go with the rate that wins most often.I got mine measured at Ayala’s tent among an unceasing line of other women at FeistyFest who all wanted to understand their bodies better, so to accommodate everyone, Ayala tested us at a five-second inhale and a seven-second exhale, which is the average for most people, just to show us what resonance frequency breathing feels like (which, if you have no way of measuring your actual HRV, could be the rate you adopt for yourself).At home, I downloaded the Elite HRV app, which synced seamlessly with my Garmin HRM-Fit heart rate monitor (other compatible devices are listed on the app’s website). Under custom breathing, I tested various inhale/exhale rates to see which produced the highest HRV. On Ayala’s recommendation, I tested first thing in the morning each time, while still lying in bed. Turns out that my body is even happier at six breaths per minute instead of five (inhale for four and exhale for six).Once you have your ratio, you can start practicing—while you’re making a coffee or sitting in traffic, doesn’t matter—the most important thing is to actually do it and let your body get used to the frequency. Meta-analyses and systematic reviews say the ideal timeframe is 10 to 20 minutes a day—for 10 to 12 weeks, Ayala adds—and you should see the results. “Research suggests stress management significantly improves depression symptoms, anxiety symptoms, feelings of stress, and then overall just nervous system function,” Ayala says. “The HRV training has been incredible because you feel it in the moment; you start to feel a weird sense of calm. It also helps in the long term, so you notice the benefits in the short term and in the long term.”Pavlína Černá, an RRCA-certified run coach and cycling enthusiast, has been with Runner’s World, Bicycling, and Popular Mechanics since August 2021. When she doesn’t edit, she writes; when she doesn’t write, she reads or translates. In whatever time she has left, you can find her outside running, riding, or roller-skating to the beat of one of the many audiobooks on her TBL list.