Cold exposure boosts vagal drive
Cold exposure prior to exercise (precooling) boosts peak power and postpones fatigue by protecting mitochondria.
A new study suggests that precooling also improves exercise capacity by strengthening vagal tone, as measured by heart rate recovery.
Deliberate cold exposure works on both the sympathetic and parasympathetic divisions of the autonomic nervous system. As a consequence, it will paradoxically scare you to death and make you feel more alive.
Precooling your workout
Joe Rogan recently created a minor sensation in the cold community by explaining, first to Derek from More Plates More Dates (#1905) and then to David Goggins (#1906) how he's been reading our articles about ice baths before exercise, and the big boost we've experienced in our testosterone as a result.
Joe admitted that it's a lot harder to get up first thing in the morning, head outside in his underwear, and do an ice bath in the cold winter air, without the benefit of warming up in the sauna or doing exercise beforehand.
When I wake up in the morning, I don't dress warm. " wear my fucking underwear, and I go outside and it's 40 degrees this morning, and I walk out and lift the lid and I see the fucking ice floating up in there. I get in there for three minutes in the morning, and then I work out." - Joe Rogan
What Rogan didn't talk about was how precooling in his Morozko ice bath changes his workout performance.
In Precool Your Workout, I described the mechanisms by which an ice bath before exercise protects mitochondria in your muscles, boosts peak performance and postpones fatigue. That story hasn't received anywhere near the same attention as the testosterone article, but since Rogan's podcast with Goggins several customers have written to tell me that they've also tried doing their ice baths before their exercise, and they've noticed a huge energy boost.
Science of ice baths for recovery
Most people are doing ice baths after exercise to reduce the pain and discomfort of delayed onset muscle soreness (DOMS, Moore et al. 2022). What they may not realize is that following high-intensity exercise with an ice bath can interfere with the processes by which the body rebuilds muscles and makes anabolic gains. For example, Andrew Huberman, PhD recommends waiting at least 4 hours after a workout before you practice deliberate cold exposure, to give the body time to benefit from the hormetic stress of the exercise.
If your main goal is hypertrophy and strength, it is probably best to avoid cold water immersion or ice bath immersion for about 4 hours or more after that training. - Huberman 2023
What Huberman has never talked about is what happens to recovery when you do your deliberate cold exposure before your exercise. He's done a whole podcast on how heat extraction during a workout (percooling) results in amazing improvements in peak power output and increases endurance (Huberman & Heller 2021), and acknowledges that percooling also reduces DOMS, but there have been new revelations related to precooling since then.
Two brand new studies have again confirmed the experience of those people who are doing their cold exposure the hard way -- before they exercise. For example, a Polish team of researchers studied 32 professional male athletes in their mid-20's who experienced two minutes in a cryochamber at −130°C prior to 40 minutes of intense cycling. Compared to a control group, cryostimulation was associated with lower blood markers of inflammation (Jurecka et al 2022). Moreover, researchers in Italy studied the effects of whole-body cryotherapy precooling on peak performance and fatigue. After three minutes of cold exposure in −150°C air, study participants exhibited a boost in both power and endurance on an exercise bike, compared to their control baseline (Storniolo et al. 2022).
Those results are consistent with prior findings measuring significant gains in all types of exercise, including runners (Spannagl et al. 2022) and cyclists (Fenemor et al. 2022). Nonetheless, two things stand out about the Italian study:
Precooling boosted exercise performance at a lower peak heart rate than controls. That is, not only did the study subjects (26 men, 2 women in their 20's) increase exercise performance, they increased cardio-vascular efficiency. To my knowledge, these results are the first under all-out exercise conditions, and reinforce the suggestion that the improvement in exercise performance is related to enhanced muscle metabolism -- i.e., mitochondrial efficiency.
Precooling accelerated recovery from exercise, as measured by time required for post-exercise heart rate to return to resting state. While cold exposure has often been advocated as a method of speeding recovery after exercise, this is the first study to suggest that doing cold exposure prior to exercise may have post-exercise recovery benefits.
Vagal drive for exercise
These new results improve understanding of the relationship between the parasympathetic division of the autonomic nervous system and exercise capacity -- something the study authors called vagal drive. The autonomic nervous system regulates involuntary physiologic processes. In other words, it causes your body to respond automatically to meet your needs without you having to think about it or decide. For example, the autonomic nervous system controls your heart rate, blood pressure, respiration, digestion, and sexual arousal.
Nonetheless, the relationship between vagal nerves and exercise capacity is not obvious. We ordinarily think of extreme exercise as associated with increased activity in the sympathetic division of the autonomic nervous system -- that division of the nervous system that activates the fight-or-flight response. The sympathetic nervous system prepares your body for immediate, life-saving action. It typically increases heart rate, causes release of glycogen stores from the liver (to fuel muscle action with glucose), and stimulates production of epinephrine (also known as adrenaline) to motivate an energetic burst.
However, the vagal nerves are part of the parasympathetic division of the central nervous that calms your body down. It is sometimes referred to as the rest-and-digest response. Human subjects with poor vagal tone can find themselves in a constant state of anxiety or agitation, from which they are unable to calm down.
Given their different actions on the body, it would be logical to think of exercise as associated with increased activity in the sympathetic division, and recovery as associated with increased activity in the parasympathetic nervous system, via the vagal nerves.
Nonetheless, vagal tone is directly related to capacity for exercise. For example, when researchers genetically engineered rats to silence vagal control, they observed diminished exercise performance. Even more remarkable, when rats were subject to artificial stimulation of the vagal controllers in their brains, they exhibited increased exercise endurance equivalent to a control group that had been exercise-trained (Machhada et al. 2017). That helps explain why elite endurance athletes typically have high vagal tone -- that is, they exhibit exceptional heart rate control, high HRV, and recover from acute exercise faster than less well-trained subjects.
In this new study on cryotherapy precooling, the researchers noticed heart rates in the control group stayed elevated for several seconds after exercise ceased. However, heart rates in the precooled group began to return to normal immediately upon cessation of exercise. In this way, the precooled subjects recovered faster than did the control group.
It is this heart rate recovery in the precooled group that is characteristic of improved vagal nerve function.
The rate of heart rate recovery (HRR) after cessation of the exhaustive exercise serves as a robust index of individual ability to recruit vagal tone. - Machhada et al. 2017
Complexity of Cold Exposure
In Ice Bath vs Cold Plunge for HRV I wrote that cold thermogenesis is activated in brown fat via the sympathetic nervous system. Unlike white fat, brown fat is highly innervated (Bartness et al. 2014), which is to say that it is well-supplied with nerve tissue to facilitate communication with the brain.
Because brown fat is positioned near the arteries that supply vital organs with warm blood -- around the clavicles, between the scapula in the back, and around the heart -- it is not able to sense cold. To stimulate cold thermogenesis, thermoreceptors of the skin must send nerve signals to the brain and into brown fat depots via the sympathetic nervous system. This mechanism explains how the ice bath initiates the involuntary fight-or-flight response, and prepares the body for action.
It is also that same sympathetic nervous system response that makes an ice bath so inexplicably scary -- what Rogan calls his "daily battle with his inner bitch."
It is fear.
That fear can be felt in the nervous system long before it is sensed by the thermoreceptors in the skin. Lewis Pugh is a world-record holder for cold, open water, endurance swimming. According to Dr. Tim Noakes, who monitored Pugh's Arctic and Antarctic ocean swims, Pugh's body temperature increased by as much a 2°C before he immersed himself in the cold water.
Dr. Noakes called it anticipatory thermogenesis, and wrote back in 2005 that "this phenomenon had not been noted in any other human."
What now seems clear is that Pugh's anticipation of the cold water caused activation of cold thermogenesis in his brown fat, exclusively through the power of his brain.
This is exactly the same claim that Wim Hof made a decade later, as Scott Carney documented in What Doesn't Kill Us (Carney 2017). Given the extreme breath control that Hof (and some monks) exhibit, it makes sense that they could activate their brown fat through their sympathetic nervous system without the benefit of signaling from their thermoreceptors -- i.e., via their thoughts alone.
As for the rest of us, without the benefit of monk-like control of our nervous system we might acquire this hidden nervous system advantage by using an ice bath to precool our workouts. Although the cold will scare us, it will also psyche us up for the challenge of exercise and, if this new study is accurate, recruit additional vagal drive.
As Rogan says, he dreads "this fucking thing every day, but I feel amazing when I get out."
When we emerge from the ice bath alive, some part of our nervous system is convinced we have cheated death.
Precooling for recovery
It has long been understood that cold exposure improves heart rate variability (HRV), which is a critical measure of vagal tone. For example, a study of 18 elite French female handball players showed significant improvement in HRV in those players who used six minutes of cold water immersion (10°C, immersed up to the navel) at the end of intense pre-season training days, compared to those who used passive recovery (Ravier et al. 2022).
It's not clear why cold exposure should paradoxically boost exercise capacity via the sympathetic nervous system when done prior to exercise, and boost recovery via the parasympathetic nervous system when done after exercise. Nonetheless, the post-exercise findings regarding HRV are consistent across several studies. For example, a study of 12 male athletes compared cold and thermoneutral water immersion for recovery from all-out sprint cycling workouts and concluded "... colder immersion temperatures (are) likely more effective at increasing parasympathetic activity" (Al Haddad et al. 2010).
Although there has been confusion about the benefits of cold water immersion following exercise, it is now clear that icing your muscles right after your workout will reduce inflammation, reduce delayed onset muscle soreness, and reduce your testosterone/anabolic response. In other words, for growing bigger, stronger muscles, you should either do your ice bath before your workout, or wait several hours after your workout, to allow your body to recover.
What this new study could be teaching us is that precooling will not only improve your muscle metabolism during your workout by protecting your mitochondria, it might also increase your exercise capacity and speed your recovery by strengthening your vagal drive. In other words, precooling might give you a heart response that is closer to that of elite athletes (like the rats that improved exercise performance exclusively by vagal stimulation) even if you aren't trained like an elite athlete, and that this precooling for recovery effect lasts long enough to persist even after short, intense workouts.
That should be enough to convince you to try your cold exposure prior to your exercise. When you do, if you are monitoring your performance, your HRV, your testosterone levels, and/or the speed of your recovery, I'd like to hear from you about your experiences.
About the Author
Thomas P Seager, PhD is an Associate Professor in the School of Sustainable Engineering at Arizona State University. Seager co-founded the Morozko Forge ice bath company and is an expert in the use of ice baths for building metabolic and psychological resilience.