How Cold Exposure Affects Focus and Muscle Growth

In the last fourth of the talk, I am going to discuss cold stress. I am smiling in the picture of my cold plunge. I usually do not smile, and I often say profane words, but we are going to talk about a different type of thermal stress: deliberate cold exposure.

There are many things we could discuss, but because of time, I will focus on a few. I will discuss increased brown adipose tissue, the thermogenic type of adipose tissue; effects on mood and cognition, which is my favorite; and mitochondrial biogenesis, the growth of new mitochondria in adipose and muscle tissue. I will also discuss precautions, because depending on the protocol, its timing, and other activities you are doing, cold exposure may blunt some muscle hypertrophy from resistance training.

Cold stress, like heat stress, causes adaptations. These adaptations depend on dose and duration. For example, people who spent one hour in 57°F water had a fivefold increase in norepinephrine. Norepinephrine is both a hormone and a neurotransmitter. As a hormone, it causes vasoconstriction, which occurs when you enter the cold. Cold exposure also increases norepinephrine in the locus coeruleus region of the brain.

Fifty-seven degrees is not warm. It feels quite cold, and who wants to do that for an hour? Fortunately, two minutes in 50°F water raises norepinephrine about twofold. This is my favorite protocol. I use about 49–50°F water for two minutes. I like the norepinephrine increase because it helps me with focus and attention, improves my mood, and seems to have an anxiolytic effect that lowers anxiety a little. Two minutes is much easier than an hour.

At 35°F, which is very cold, 20 seconds has also been associated with a twofold increase in norepinephrine. Staying for two minutes instead of 20 seconds would probably increase the norepinephrine response more. The bottom line is that the response depends on dose and duration.

There is evidence that cold increases norepinephrine in the brain. It is not only a hormonal response. Anyone who has done deliberate cold exposure knows that you can feel it immediately.

One small cohort study involved people with major depressive disorder who received cryotherapy. This was not cold-water immersion. Participants entered chambers filled with very cold air. Researchers wanted to examine how it affected mood. There was a treatment group and a sham-control group. The treatment group received approximately −256°F, while the sham control received approximately −58°F. A placebo group is important when studying depression because the placebo effect can itself produce an antidepressant response.

People who received two minutes at −256°F five times per week for two weeks had a large improvement in depressive symptoms. Their Hamilton Depression Rating Scale score improved by about 17 points. For context, a change of approximately 2.5 points is considered clinically relevant.

Now let us shift to deliberate cold exposure, thermogenesis, and brown adipose tissue. Norepinephrine is one of the regulatory responses. In the vascular system, norepinephrine acts as a signaling mechanism. It increases a protein called UCP1, which signals adipose tissue to make more mitochondria.

This is an adaptation. The more mitochondria you have in adipose tissue, the more energy you can burn and the more heat you produce as a byproduct. The body adapts to survive in the cold by making more mitochondria. Stored fatty acids undergo lipolysis and are metabolized for energy, and heat dissipates to warm you.

The more you expose yourself to cold, the more brown fat you begin to make. Researchers are interested in ways to increase brown adipose tissue and mitochondrial biogenesis because this could increase energy expenditure and improve metabolic health.

In one study, young, healthy men wore a cooling suit that cooled them to about 50°F for two hours per day. After one month, they had an almost 50 percent increase in brown adipose tissue. I have seen other studies in which 15 minutes in 50°F water increased mitochondrial biogenesis in adipose tissue. Fifteen minutes is difficult, but cold exposure becomes easier after about four minutes.

Adipose tissue is not the only tissue in which mitochondrial biogenesis occurs in response to deliberate cold exposure. It also increases in muscle. When you are exposed to cold, norepinephrine increases. That increases PGC-1α, which then increases mitochondrial content in muscle tissue. This is associated with less muscle atrophy and improved endurance performance.

Several studies involving elite tennis players, rowers, and endurance runners have found that deliberate cold exposure between exercise bouts improved measures such as running time or reaction time. These findings are specific to endurance-type activities.

The best way to increase mitochondrial biogenesis in muscle is high-intensity interval training. It is much more robust than deliberate cold exposure. But cold exposure also increases mitochondrial biogenesis as an adaptive response. A protocol of approximately 15 minutes at 50°F may increase mitochondrial biogenesis in muscle and adipose tissue. Brown adipose tissue gets its name because fat droplets with more mitochondria look browner under a microscope.

It is important to point out that deliberate cold exposure after resistance or strength training can blunt some anabolic effects when you are trying to increase muscle protein synthesis and hypertrophy. Multiple studies have shown this. In recent work from Luc van Loon and colleagues, cold-induced vasoconstriction reduced the delivery of amino acids, inflammatory signals, and growth factors to muscle for a period after training. Participants still experienced some muscle hypertrophy, but it was blunted compared with a control group.

If you are trying to maximize muscle gains, it is a good idea to avoid cold-water immersion, cryotherapy, or another deliberate cold-exposure method around resistance training. The safest options are recovery days, days with endurance training such as a run or zone 2 session, or many hours before or after resistance training. Otherwise, you may blunt muscle protein synthesis.

To summarize the protocols: if you want a brief cognitive boost or norepinephrine response before sitting at your desk, giving a talk, or doing something cognitively demanding, you can use a high-intensity interval protocol or approximately two minutes at 50°F. Another option is approximately 20 seconds at 35°F.

For mitochondrial biogenesis in adipose or muscle tissue, the key protocol discussed here is approximately 15 minutes at 50°F. Once you adapt, it becomes easier because you have more brown adipose tissue and the water does not feel as cold. That adaptation disappears quickly if you stop, so you have to readapt.