Shulou(Shulou.com)11/24 Report--

(photo Source: pxhere) not long after the Beginning of Winter, the cold air caught people off guard, wanting to go to work and school wrapped in quilts every day, becoming one of the "penguins" who had difficulty walking and shaking their heads on the street.

(Tuyuan Gifer) however, there are always a few people in the crowd who dress very little, as if those who are spending the summer are so eye-catching that those who see them can't help but shudder:

"Why are people so unafraid of the cold? I want to be as cold-resistant as he is!"

"Why do I have to wear a down jacket and three layers of long johns when he can wear short-sleeved shorts in the same weather?"

"do people who love winter swimming have any superpowers?"

"what caused us to be frozen at the starting line?"

It's like my dream life... | the cause of Twitter is actually a bit complicated. Human tolerance to cold depends on genetic factors, subcutaneous fat thickness, body size, and so on. Some scientists have pointed out that when the body temperature drops, the rate at which we release energy from muscle cells slows down to maintain body temperature.

But some people really have a congenital advantage in cold resistance-genetic variation!

Human skeletal muscle is mainly composed of two types of fibers: slow tic muscle fiber (Slow-twitch Skeletal Muscle) and fast twitch muscle fiber (Fast-twitch Skeletal Muscle).

If you look at muscle cells under microscope, you can see that the dark area is slow muscle fiber, and the white area is fast muscle fiber. References [1] slow twitch muscle fibers are generally responsible for slower aerobic exercise, durable and better tolerant to low temperature. Fast twitch muscle fibers will twitch quickly, responsible for more powerful jumping, sprint and other explosive exercise or anaerobic exercise, which can quickly consume energy and make you more prone to fatigue.

Comparison of people with two types of muscle fibers [2] take chicken as a simple example, which may help us to understand the difference between the two types of muscle fibers.

Chicken legs need to walk for a long time, so slow muscle fibers and myoglobin are denser, and because myoglobin is rich in iron, the chicken leg is dark red.

Chicken breast muscle only needs to carry out short, intense and anaerobic explosive activities when birds flap their wings, and the fast muscle fiber density is high, so the chicken breast meat color is light powder.

Left chicken leg meat, right chicken breast meat (this comparison is still very clear. Wikipedia the ratio of slow twitch muscle fiber to fast twitch muscle fiber in each person's muscle varies from person to person, and people will automatically choose the appropriate motor muscle unit according to their needs during exercise.

The proportion of fiber types of non-sports individuals is close to 1:1, while strength athletes have a higher proportion of fast tic muscle fibers. for example, sprinters have 70% to 75% of fast tic muscle fibers. while endurance athletes (such as long-distance runners) account for 80% to 85% of slow twitch muscle fibers.

This explains why some people are suitable for weightlifting that requires explosive force, while others are more suitable for long-distance cycling.

Ah, there's a reason why it's not suitable for running. | is there any deep relationship between Twitter slow and fast twitch muscle fibers and the body's cold resistance? There is!

According to Loss of α-actinin-3 during human evolution provides superior cold resilience and muscle heat generation, a paper published in the journal American Journal of Human Genetics in 2021, the researchers recruited 42 healthy men between the ages of 18 and 40 and asked them to soak in cold water for 20 minutes in 14 ℃ and then take a 10-minute break at room temperature until their body temperature dropped to 35.5 ℃.

During immersion, the researchers used electromyography (EMG) to measure muscle electrical activity, evaluate human tremor, and collect muscle biopsies to study protein content and fiber type composition.

Admire the courage of the participants. YouTube researchers at Karolinska Institute in Sweden found that:

1. Twenty percent of the participants lacked alpha-actin-3 (ACTN3), or genetic mutants, in their fast twitch muscle fibers.

two。 Only 30 per cent of genetically normal participants maintained their body temperature above 35.5 ℃; those with genetic mutations performed well, with 69 per cent keeping their body temperature above 35.5 ℃ after exposure to cold water, with a slow drop in body temperature and little tremor.

α-actin-3 | Wikipedia so how do people with these genetic mutations maintain their body temperature and resist the cold?

The study found that such people activate slow twitch muscle fibers and release calcium ions, generating more heat by increasing muscle tension.

The decrease rate of rectal, muscle and skin temperature in B-D:XX group (lack of gene) was lower than that in RR group (without gene deficiency), and the heart rate and lung O _ 2 uptake rate and CO _ 2 exhalation rate in E-G:RR and XX groups before and after cold water immersion. | reference [4] however, skeletal muscle is not the only thermogenic pathway in the human body. Does brown adipose tissue, other thermogenic organs, generate heat in the experiment and affect the experiment?

In order to eliminate the interference factors, the researchers used mice with α-actin-3 deficiency as experimental materials. They observed that the brown adipose tissue properties of mice with genetic mutations did not change at all.

In other words, the reason why the gene mutants were able to maintain body temperature during the experiment was due to the activation of slow twitch muscle fibers, and the warming effect of brown adipose tissue was negligible.

Fifty thousand years ago, human ancestors who migrated from Africa to Europe lost alpha-actin-3 in their fast twitch muscle fibers, which helped them better cope with cold climates and efficiently use slow twitch fibers to save energy. instead of wasting energy on shivering.

But in today's society, evolutionary advantages and health risks coexist.

"people with genetic mutations are more likely to suffer from obesity, type 2 diabetes and other metabolic disorders," the researchers said. they also have a higher risk of falling in old age because they have fewer rapid twitch muscle fibers than genetically normal people and are not suitable for controlling strength and explosive exercise. "

After weighing the pros and cons, which ability do you prefer to have?

Reference:

[1] https://m.blog.naver.com/natboy0611/220663756757

[2] https://www.verywellfit.com/fast-and-slow-twitch-muscle-fibers-3120094

[3] https://www.inverse.com/mind-body/gene-variant-tolerate-the-cold-study

[4] https://doi.org/10.1016/j.ajhg.2021.01.013

[5] https://www.frontiersin.org/articles/10.3389/fphys.2017.01080/full

This article comes from the official Wechat account: take Science Home (ID:steamforkids), written by A Xian, revision: Skin

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