근섬유(근육)의 작동 원리와 성장 방법

안녕하세요😃

저번 포스팅에서는 근육의 분류부터 시작해 설명들로 주를 다뤘다면 오늘은 조금 더 작은 단위로 들어 가 볼까 합니다.

더 나아가 작은 단위 즉, 근섬유를 알아보고 우리가 운동을 했을 때 어떻게 성장이 이루어 지는지도 알아보도록 하겠습니다.

 

 

개별 근육을 최소 단위까지 들어가보면 다음과 같습니다.

-        개별근육—근섬유—근원섬유—근원세사

여기서 근섬유는 우리가 중요하게 생각하는 골격근을 이루는 핵심 단위입니다. 근섬유는 일반적인 조직 세포와는 많이 다르지만 같은 기관을 가지고 있으며 에너지 대사, 회복, 수축, 이완까지 할 수 있는 독립적인 가장 작은 단위입니다.

근섬유는 아래의 사진과 같이 구성되어 있습니다. 근섬유막이라는 원형질막이 근섬유를 두르고 있으며 안쪽을 뜯어보면 액틴과 미오신이 합쳐져 있는 근원섬유가 있습니다. 

이 근원섬유 주변을 근육세포질망이라는 보조 조직이 그물처럼 휘감고 있습니다.

근원섬유가 근육의 수축을 담당하는 핵심이라면 그것을 돕는 보조 조직으로 신경의 전기 신호를 근원섬유에 전달하는 가로 세관,에너지를 내는 미토콘드리아, 세포핵, 근섬유가 다쳤을 때 치료를 해주는 위성세포가 분포하고 있습니다.

즉 하나의 근섬유는 완벽한 체계를 갖추어 독자적으로 움직일 수 있는 것이죠.

근섬유의 굵기는 머리카락 정도지만 사람마다 차이가 조금 있다고 하며 여성보다는 남성이 대체로 굵습니다.

 

 근섬유에서 전기 신호에 의해 수축을 담당하는 근원섬유 다음으로 중요한 것을 꼽으라고 한다면 바로 미토콘드리아입니다.

미토콘드리아는 에너지 ATP를 공급하기 때문이죠.

사실 미토콘드리아는 처음부터 세포의 한 축을 담당하는 아이는 아니었습니다.

기존에는 산소호흡 박테리아로 독자적인 생활을 했지만 어느 시점에서 진핵세포의 일부로 들어와 공생한 것으로 추정이 되고 있습니다.

미토콘드리아는 난자를 통해 모계 유전자로만 전달되기 때문에 mDNA는 모계펼통을 확인하는 수단으로 자주 사용됩니다.

근섬유 속 미토콘드리아는 산소를 잘 태우는 능력을 발휘해 탄수화물과 지방을 산소와 함께 태워 높은 에너지 분자인 ATP로 바꿔주는 일을 전담 하고 있습니다.

결과적으로 보면 근섬유 측은 힘들지만 필요한 일을 하청을 주고 미토콘드리아는 근섬유에게 기생하여 안식처를 얻을 수 있으니 서로 윈-윈이 된 장사같네요.

미토콘드리아는 세포 하나에 1천 개 이상 들어 있으며 에너지 소모가 많은 기관일수록 수가 많습니다. 나아가 달리기와 같은 지구력을 요하는 운동을 하면 추가로 번식하며 크기도 커집니다.

이렇게 미토콘드리아가 발달한 사람들은 에너지를 내는 능력이 발달 됩니다.

그렇기 때문에이 기생체의 발달은 운동 능력 향상에 지대한 영향을 미치게 되는 중요한 요소가 되었습니다.

 

 

자 그럼 이제는 근육이 어떻게 힘을 내는 지 알아보겠습니다.

쉽게 말하자면 근육은 자극을 받아 수축은 할 줄 알지만 밀어내지는 못합니다.

아까 말한 근원섬유 안에 있는 액틱관 미오신은 원래 친하지가 않은 지 떨어져 있다가 전기 신호가 전해지면 칼슘이온이 방출되면서 순간적으로 이어지며 수축을 시작합니다.

근육이 완전한 이완상태 즉, 액틴과 미오신이 분리되어 있는 상태에서 수축을 하기까지는 다소 시간이 걸립니다.

예를 들어 우리가 침대에 누워있다가 펄쩍 뛰어오르며 완전한 힘을 내지 못한다고 생각하면 쉬울 것 같습니다. 

여기서 나타나는 단어가 바로 예비 부하입니다.

수축 전에 약간의 힘이 가해지면 이런 수축이 훨씬 빠르고 강하게 일어납니다.

이해를 돕기 위해 데드리프트로 설명 해 보겠습니다. 저희는 컨벤셔널 데드리프트를 할 때 땅에서 아무렇지 않게 바를 뽑아 올리지 않습니다. 

먼저 봉을 쥐고 발바닥부터 시작한 근육들의 긴장을 머리끝까지 가져간 후 바와 기싸움을 하며 근육들의 텐션을 올리죠.

바로 그것들이 예비 부하입니다. 이름만 번지르르 하지 막상 저희 근처에 다 있는 것들이죠.

이런 예비 부하때문에 운동을 수행하는 중에도 힘을 완전히 뺴서는 안되는 것입니다.

 

 

이번엔 예비 부하와 비슷한 예비 신장을 알아볼까요?

벌써부터 머리가 아파올 수 있지만 요즘은 흔히들 쓰는 말 즉, 치팅입니다.

근육을 수축시키기 전에 주동근과 반대되는 길항근을 써서 당기면 늘어난 고무줄처럼 원래 상태로 돌아가려는 힘이 생기죠.

복싱 선수들이 주먹을 뻗을 때 가슴 근육을 뒤로 쭉 늘려 준 후 등 근육으로 강하게 뻗는다라고 생각하면 이해가 쉬울 것입니다.

이렇게 되면 길항근과 주동근의 힘이 합쳐져 실제 근력보다 큰 힘을 내게 되죠. 

예비 신장을 과하게 쓰면 목적했던 주동근이 아닌 주변 엉뚱한 근육이 더 자극되는 운동이 되기도 하기에 전통적인 근력 운동에서는 치팅을 원칙적으로 금하거나 반기지 않습니다.

정자세로 제어하지 못하는 중량은 관절이 고스란히 받아 부상 위험도도 높습니다.

하지만 예비 신장이라는 것은 제한된 근육을 최대한으로 사용하는 기술 중 하나라고 보면 어떨까요? 크로스핏이나 파워리프팅 등 협응력과 실질적인 면을 중요시하는 종목에서는 의도적으로 이용하기도 합니다.

 

 

그렇다면 근섬유의 구성과 작동 원리도 알았는데 대체 근육은 어떻게 성장하는데?

그 질문에 대해서는 이제 적어보겠습니다.

기본적으로 잘 먹고 열심히 운동을 해야합니다해야 합니다.그러면 근육은 자랍니다. 하지만 아무 운동에서나 성장하지는 않죠.

여기서 말하는 근육이 성장하는 운동은 개인의 역치를 넘어서는 운동을 말합니다.

매일 같은 무게, 같은 반복 횟수, 같은 시간 운동을 해서는 역치를 넘어 설 수 없으니 몸도 근육도 그대로입니다.

근육의 성장을 도모한다면 중량이든, 시간이든, 반복 횟수든, 집중력이든 운동 강도가 ‘역치’를 넘어야 합니다.

하지만 이 역치에는 심리적인 부분도 작용 한다는게 상당한 문제입니다.

우리의 몸은 80% 정도의 힘을 내고 있지만 우리의 뇌는 그렇게 생각하지 않는다는 말입니다.

(이 말에 대해서는 저조차도 잘 지키지 못하고 있습니다. 컨디션 등 온갖 핑계를 대며 그 상태에 머무르고 말죠…)

이러한 심리적인 부분도 이겨내고 신체적인 한계를 뛰어넘을 때 우리의 근육이 성장하게 됩니다.

괜히 트레이너들이 옆에서 계속 개수를 거짓말 치며 더 시키는 것이 아닙니다 😭

 

 

그렇다면 이 모든 것들을 극복 해내고 근육이 성장이 하게 되었을 때 무엇이 커지게 되는 것일까요?

통상적인 설에 따르면 포유동물은 태어날 때 근섬유나 그 원형을 가지고 태어나며 이후로는 더 이상 분열 하지 않는다고 합니다. 즉 일반적인 세포가 분열해서 근섬유가 많아지는 게 아니라는 것이죠.

운동을 하게 되면 해당 부위 근육의 하부 단위인 근원세사가 상처를 입습니다.

그럼 위성세포가 손상 부위와 융합 해 복구를 진행하는데 복구와 함께 세포질 망,미토콘트리아도 늘어나며 신경조직까지 촘촘해지며 근육이 비대 해집니다.

여기서 근섬유와 합체를 한 위성세포는 새로운 근육 세포 핵이 되게 되는데 이후에 운동을 중단해도 사라지지 않고 남아 있습니다.

그래서 전에 운동을 했던 사람이 일정 기간 운동을 쉬어도 재개 했을 때 경험이 없던 사람보다 빠르게 이전 상태로 회복하게 됩니다.

 

 

이렇게 오늘은 근육의 하부 단위부터 작동 원리, 성장 원리까지 알아보는 포스팅을 작성 작성했습니다.짧지 않은 글 읽어주셔서 감사합니다.🙇🏻‍♂️

 

 

 

 

Exploring Muscle Fibers: How Muscles Work and Grow

Hello! 😃

In our previous post, we covered the basic classification of muscles, but today we’re going to dive even deeper into the smaller components that make up your muscles: muscle fibers. We'll also explore how they grow in response to exercise.

Breaking Down Muscle Structure

At the smallest level, muscles can be divided into the following components:

• Individual Muscle → Muscle Fiber → Myofibril → Sarcomere

Muscle fibers form the core units that make up skeletal muscles, which are the muscles we focus on when discussing fitness. While muscle fibers share some similarities with regular tissue cells, they are specialized for energy metabolism, contraction, relaxation, and recovery, making them the smallest independent functional units of muscle.

If we look inside a muscle fiber, it's encased in a plasma membrane called the sarcolemma, and inside are myofibrils, composed of two key proteins: actin and myosin. Surrounding these myofibrils is a network of support structures like the sarcoplasmic reticulum, which plays a role in transmitting electrical signals to the myofibrils for muscle contraction.

In addition to the myofibrils, which drive muscle contraction, other important elements include:

• T-tubules: which deliver nerve signals to the myofibrils
• Mitochondria: which generate energy
• Nuclei: that control cell activity
• Satellite cells: that help repair damaged muscle fibers

Each muscle fiber is essentially a well-organized unit capable of functioning independently, and though they are only about as thick as a human hair, their size and number can vary between individuals, with men generally having thicker fibers than women.

The Role of Mitochondria: The Energy Powerhouse

Besides the myofibrils, another crucial component within muscle fibers is the mitochondria. These tiny organelles produce ATP, the energy source muscles need to function. Interestingly, mitochondria weren’t always part of muscle cells. They were originally independent bacteria that later merged with eukaryotic cells in a symbiotic relationship.

Mitochondria are maternally inherited, meaning they are passed down through the mother’s genetic line, which is why mitochondrial DNA (mDNA) is often used to trace maternal ancestry. Inside muscle fibers, mitochondria use oxygen to burn carbohydrates and fats, converting them into ATP, which provides energy for muscle contractions.

Each cell contains over a thousand mitochondria, with the number increasing in tissues that require more energy, like muscles. Endurance training, such as running, can boost both the size and number of mitochondria, improving your body’s energy production capabilities. This makes mitochondria a key player in enhancing athletic performance.

How Muscles Generate Force

Now, let’s take a closer look at how muscles actually generate force. In simple terms, muscles contract in response to electrical signals but cannot push; they can only pull.

Inside each myofibril, actin and myosin, which normally don’t interact, are triggered by an influx of calcium ions when an electrical signal is received. This causes the two proteins to bind momentarily, leading to muscle contraction. However, for a muscle to contract fully from a relaxed state, it takes some time.

This is where the concept of preload comes into play. Preload refers to the slight tension placed on muscles before a contraction, allowing for a faster and more forceful contraction. A good example is the deadlift. When performing a conventional deadlift, you don’t just pull the bar off the ground immediately; you first engage your muscles and create tension before lifting. This buildup of tension is an example of preload.

Pre-stretching and Muscle Force

Another concept similar to preload is pre-stretching, also known as cheating in the fitness world. Pre-stretching involves using opposing muscles (antagonists) to pull a muscle before contracting it, creating a "rubber-band effect." This principle can be seen in sports like boxing, where fighters pull their chest muscles back before launching a punch, combining the force of both antagonist and agonist muscles for a more powerful movement.

However, while pre-stretching can enhance performance, it can also lead to improper muscle engagement or even injury if overused. That’s why traditional strength training discourages excessive cheating, as it can stress joints and increase the risk of injury. Yet, in functional sports like CrossFit or powerlifting, where coordination and practical strength are key, pre-stretching can be used intentionally.

How Do Muscles Actually Grow?

Now that we’ve covered how muscle fibers work, you might be wondering: how do muscles actually grow?

To stimulate muscle growth, you need to engage in exercises that push your body beyond its current limits, often referred to as progressive overload. Simply repeating the same weights, reps, and intensity won’t challenge your muscles enough to prompt growth. Whether it’s by increasing weight, repetitions, time under tension, or focus, your workout intensity must exceed your body’s threshold to promote muscle adaptation.

Interestingly, overcoming the mental barrier is just as important. While your body might be capable of exerting 80% of its strength, your brain often limits your perceived effort. This is why personal trainers constantly push you to complete a few more reps—they’re helping you break through this psychological barrier.

What Exactly Grows When Muscles Get Bigger?

Contrary to popular belief, muscles don’t grow by creating new fibers. Instead, when you’re born, the number of muscle fibers you have is largely fixed. What changes with exercise is the hypertrophy of these fibers.

When you exercise, particularly with heavy weights, your myofibrils undergo micro-damage. In response, satellite cellsstep in to repair the damaged fibers, adding new structures like mitochondria and thickening the muscle. These satellite cells also become new nuclei within the muscle fiber, helping the muscle adapt to future demands.

What’s interesting is that once these satellite cells fuse with the muscle fiber, they remain there even if you stop exercising. This is why people who have trained before can "bounce back" to their previous fitness level faster than someone who has never exercised—it’s known as muscle memory.

Final Thoughts

In this post, we’ve explored the structure of muscle fibers, how they function, and how they grow. Understanding these basics can help you optimize your workouts for better results. Thank you for reading, and I hope this deep dive into muscle fibers has been helpful! 🙇🏻‍♂️