움직임을 위한 근육 탐구 - 정리중

[문형철]

http://downloads.lww.com/wolterskluwer_vitalstream_com/sample-content/9780781791281_Hamill/samples/Hamill_ch03_063-104.pdf

After reading this chapter, the student will be able to:

1. Define the properties, functions, and roles of skeletal muscle.

    골격근육의 특성, 기능,역할을 정의할 수 있어야

2. Describe the gross and microscopic anatomical structure of muscles.

    근육의 대, 소 해부학적 구조를 묘사할 수 있어야

3. Explain the differences in muscle fiber arrangement, muscle volume, and cross-section

as it relates to the output of the muscle. 

    근섬유 배열, 근육용량, 단면과 관련된 근육의 힘사용과 관련된 차이점을 설명할 수 있어야

4. Describe the difference in the force output between the three muscle fiber types(types I, IIa, IIb).

    세가지 근육타입의 힘분출의 차이점에 대해서 설명할 수 있어야

5. Describe the characteristics of the muscle attachment to the bone and explain the viscoelastic response of the tendon. 

    뼈에 부착된 근육의 특성을 묘사하고 건의 점탄성 반응을 설명할 수 있어야

6. Discuss how force is generated in muscle.

    근육에서 힘의 생성이 어떻게 이루어지는지 토론할 수 있어야

7. Describe how force is transmitted to bone.

    뼈에 힘의 전달이 어떻게 이루어지는지 토론할 수 있어야

8. Discuss the role of muscle in terms of movement production or stability.

    힘의 생성이나 안정성 개념에서 근육의 역할에 대해서 토론할 수 있어야

9. Compare isometric, concentric, and ecccentric muscle actions.

    등척성, 구심성, 원심성 근육활동을 비교할 수 있어야

10. Describe specific considerations for the two joint muscles.

    다관절근육을 특이한 고려에 대해서 묘사할 수 있어야

11. Discuss the interaction between force and velocity in the muscle.

    근육에서 힘과 속도의 상관관계에 대해서 토론할 수 있어야

12. Describe factors that influence force and velocity development in the muscle, including muscle cross-section and length, the length–tension relationship, neural activation, fiber type, the presence of a prestretch, and aging.

    근육에서 힘과 속도에 영향을 주는 요소를 설명할 수 있어야. ...     

   근육의 단면, 근육의 길이, 근육길이와 장력관계, 신경활성화, 근섬유 타입, 스트레치전과 노화 등을 포함

13. Explain the physical changes that occur in muscles as a result of strength training and elaborate on how training specificity, intensity, and training volume influence strength training outcomes.

    근육의 근력트레이닝 결과에 대한 물리적 변화에 대해서 설명하고, 트레이닝 특성, 강도, 용량에 따른 차이를 설명

14. Describe types of resistance training and explain how training should be adjusted for athletes and nonathletes.

    저항트레이닝의 종류에 대해서 설명하고, 달리기와 비달리기를 위해 어떻게 조절되어야 하는지 설명할 수 있어야

15. Identify some of the major contributors to muscle injury, the location of common injuries, and means for prevention of injury to muscles.

    근육손상, 흔한 근손상부위, 근육손상 방지를 위한 방법에 대해서 설명할 수 있어야

근육섬유의 특성

Muscle tissue is very resilient and can be stretched or shortened at fairly high speeds without major damage to the tissue. The performance of muscle tissue under varying loads and velocities is determined by the four properties of the muscle tissue: irritability, contractility, extensibility,  and elasticity.  A closer examination of these properties as they relate specifically to skeletal muscle tissue will enhance understanding of skeletal muscle actions described later in the chapter.

1. 흥분성( Excitability, Irritability) - 자극에 반응하는 능력, 자극은 근수축을 생산함.  

                         - 근육은 우리 몸에서 가장 민감하고 반응조직임. 오직 신경이 근육보다 좀더 민감함. 

Irritability, or excitability, is the ability to respond to stimulation. In a muscle, the stimulation is provided by a motor neuron releasing a chemical neurotransmitter. Skeletal muscle tissue is one of the most sensitive and responsive tissues in the body. Only nerve tissue is more sensitive than skeletal muscle. As an excitable tissue, skeletal muscle can be recruited quickly, with significant control over how many muscle fibers and which ones will be stimulated for a movement.

2. 수축성(Contractility) - 근육이 짧아지거나 수축하는 능력, 근육이 늘어난 마지막단계에서 장력이 증가함. 

                                        근육의 길이는 짧아지거나 늘어나거나 동일한 길이를 유지할 수 있음. 

                                         근육은 안정길이에서 평균 57%까지 짧아질 수 있음. 

 Contractility is the ability of a muscle to generate tension and shorten when it receives sufficient stimulation. Some skeletal muscles can shorten as much as 50% to 70% of their resting length. The average range is about 57% of resting length for all skeletal muscles. The distance through which a muscle shortens is usually limited by the physical confinement of the body. For example, the sartorius muscle can shorten more than half of its length if it is removed and stimulated in a laboratory, but in the body,  the shortening distance is restrained by the hip joint and positioning of the trunk and thigh.

참고) 전도성(conductivity) - 신경의 기능.... t - tuble에서 전도성이라고 해도 되나? 

3. 신장성(Extensibility)

                   - 힘에 반응하여 안정길이(resting length)를 넘어서 늘어나는 능력

                   - 골격근은 외부의 힘이 주어지지 않으면 스스로 안정길이를 넘어서 신장되는 것은 불가능  

                   - 근육이 늘어나는 정도는 근육을 둘러싼 결합조직에 의해서 결정됨.

 Extensibility is the muscle’s ability to lengthen, or stretch beyond the resting length. The skeletal muscle itself cannot produce the elongation; another muscle or an external force is required. Taking a joint through a passive range of motion, that is, pushing another’s limb past its resting length, is a good example of elongation in muscle tissue. The amount of extensibility in the muscle is determined by the connective tissue surrounding and within the muscle.

4. 탄력성(Elasticity) - 늘어나는 힘이 제거될 때 안정길이로 되돌아가는 능력, 

                                   - 안정길이로 돌아가는 것은 근수축보다는 결합조직덕분임. 

                                   - 신장성과 탄력성덕분에 근육은 안정길이를 유지하면서 보호를 받음. 

                                   - 인대는 늘어나면 laxicity가 발생하여 원래길이로 되돌아오지 못함. 

Ability to recoil when stretch force is removed and muscle returns to its resting length(안정길이)

 Elasticity is the ability of muscle fiber to return to its resting length after the stretch is removed. Elasticity in the  muscle is determined by the connective tissue in the muscle rather than the fibrils themselves. The properties of elasticity and extensibility are protective mechanisms that maintain the integrity and basic length of the muscle. 

Elasticity is also a critical component in facilitating output in a shortening muscle action that is preceded by a stretch. Using a ligament as a comparison makes it easy to see how elasticity benefits muscle tissue. Ligaments, which are largely collagenous, have little elasticity, and if they are stretched beyond their resting length, they will not return to the original length but rather will remain extended. This can create laxity around the joint when the ligament is too long to exert much control over the joint motion. On the other hand, muscle tissue always returns to its original length. If the muscle is stretched too far, it eventually tears.

근육의 기능

 Skeletal muscle performs a variety of different functions, all of which are important to efficient performance of the human body. The three functions relating specifically to human movement are contributing to the production of skeletal movement, assisting in joint stability, and maintaining posture and body positioning.

골격근의 중요한 3가지 기능

1. 움직임의 생성

2. 관절안정성을 도움

3. 신체의 위치와 자세를 유지

PRODUCE MOVEMENT

 Skeletal movement is created as muscle actions generate tensions that are transferred to the bone. The resulting

movements are necessary for locomotion and other segmental manipulations.

골격움직임은 근육 활동이 뼈를 움직이는 장력을 만들어내면서 발생함. 그 결과로 인체는 이동과 다른 동작을 수행함. 

MAINTAIN POSTURES AND POSITIONS

 Muscle actions of a lesser magnitude are used to maintain postures. This muscle activity is continuous and results in small adjustments as the head is maintained in position and the body weight is balanced over the feet.

근육활동의 작은 양은 자세를 유지하는데 사용. 자세유지를 위해 사용하는 근육활동은 지속적이면서 작은 조정의 결과임. 예를들어 머리를 유지하고 발에 체중을 싫어 균형을 유지하는 것..

STABILIZE JOINTS

 Muscle actions also contribute significantly to stability of the joints. Muscle tensions are generated and applied

across the joints via the tendons, providing stability where they cross the joint. In most joints, especially the shoulder and the knee, the muscles spanning the joint via the tendons are among the primary stabilizers.

근육활동은 관절의 안정성에 중요한 공헌을 함. 근육장력이 생성되고, 건을 넘어 관절에 적용되면서 관절안정성을 제공함. 

OTHER FUNCTIONS

 The skeletal muscles also provide four other functions that are not directly related to human movement. 

First, muscles support and protect the visceral organs and protect the internal tissues from injury. 

Second, tension in the muscle tissue can alter and control pressures within the cavities. 

Third, skeletal muscle contributes to the aintenance of  body temperature by producing heat. 

Fourth, the muscles control the entrances and exits to the body through voluntary control over swallowing, defecation, and urination.

골격근의 구조

골격근의 물리적 조합(physical organization)

cf) The bones (tibia and fibula) together with the interosseous membrane and fasciae divide the leg into three separate

compartments: anterolateral, lateral and posterior. They contain the so-called extrinsic foot muscles. Each compartment has its own blood supply and innervation.

1. 근육 그룹(groups of muscle)

Groups of muscles are contained within compartments that are defined by fascia,  a sheet of fibrous tissue. The compartments divide the muscles into functional groups, and it is common for muscles in a compartment to be innervated by the same nerve. 

- 근육그룹은 하나의 근막으로 둘러쌓여진 구획내에 포함된 근육임. 아래 그림과 같이 근육은 동일한 근막으로 둘러싸여있고, 동일한 신경의 지배를 받기 때문에 그룹을 이루어 기능을 유지함. 

The thigh has three compartments: the anterior compartment, containing the quadriceps femoris; the posterior compartment, containing the hamstrings; and the medial compartment, containing the adductors. Compartments for the thigh and the leg are illustrated in Figure 3-2.

- 대퇴는 세 구획을 나뉨. 대퇴사두근을 포함한 전방구획, 햄스트링을 포함한 후방구획, 내전근을 포함한 내측구획. 

예) 대퇴의 전방구획 - femoral nerve 지배

The anterior fascial compartment of thigh contains the knee extensors and hip flexors.

It contains the following five muscles:^[1]

• sartorius (the longest muscle in the human body)
• quadriceps (rectus femoris, vastus lateralis, vastus intermedius, vastus medialis)

The muscles of the anterior compartment of the thigh (as well as the pectineus of the medial compartment) are innervated by the femoral nerve. Though the iliopsoas is sometimes considered a member of the anterior compartment muscles,^[2][3] the iliacus and the psoas portions do not share the same innervation. Whereas the iliacus is innervated by the femoral nerve, the psoas is innervated by ventral rami of L1-L3. Notably, thearticularis genu is also sometimes included in the anterior compartment group.^[2]

대퇴 전방구획 근육은 무릎신전, 고관절 굴곡근으로 5개의 근육(봉공근, 대퇴사두근)

치골근은 femoral nerve지배를 받으므로 전방구획으로 간주됨. 

장요근은 장골근과 대요근으로 나누는데, 장골근은 femoral nerve가 지배하고, 대요근은 L1~3 ventral rami에 의해서 지배

예) 대퇴의 후방구획 - 좌골신경의 지배

The posterior fascial compartment of the thigh contains the knee flexors and hip extensors.

It consists of the following muscles:^[1][2]

• biceps femoris
• semitendinosus
• semimembranosus

The muscles here (except for the short head of the biceps femoris) are the hamstrings. These muscles are mainly innervated by the sciatic nerve, specifically the tibial nerve. The short head of the biceps femoris is innervated by the fibular nerve. The tendons of the above muscles can be felt as prominent cords on both sides of the fossa—the biceps tendon on the lateral side and the semimembranosus and semitendinosus tendons on the medial side. The hamstrings flex the knee, and aided by the gluteus maximus, they extend the hip during walking and running. The semitendinosus is named for its unusually long tendon. The semimembranosus is named for the flat shape of its superior attachment.^[3] The arteries of the posterior compartment of the thigh arise from the inferior gluteal and the perforating branches of the profunda femoris.^[4]

대퇴의 후방구획은 무릎굴곡, 고관절 신전근육으로 대퇴이두근, 반건양근, 반막양근

대퇴이두근의 short head를 제외하고 햄스트링임. 이 근육은 주로 좌골신경에 의해 지배를 받음(특히 tibial nerve). 대퇴이두근의 short head는 fibular nerve가 지배함. 이 근육은 대둔근을 도와 고관절을 신전시키는 역할. 반건양근은 긴 힘줄 때문에 이름 지워짐. 반막양근은 형태때문에 이름 지워짐. 

예) 대퇴의 내측구획 - 폐쇄신경의 지배

The medial fascial compartment of thigh contains the hip adductors.

The obturator nerve is the primary nerve supplying this compartment.

The muscles in the compartment are:

• gracilis
• adductors
  • adductor longus
  • adductor brevis
  • adductor magnus

The obturator externus muscle is sometimes considered part of this group,^[1][2][3] and sometimes excluded.^[4] (Spatially, it is it in this location, but functionally, it is more similar to the other lateral rotator group muscles). The pectineus is sometimes included in this group,^[1][3] and sometimes excluded.^[2][4] (It has the same function as the others in this group, but different innervation.)

대퇴내측 구획은 고관절 내전근으로 폐쇄근의 지배

박근, 내전근(장내전근, 단내전근, 대내전근)으로 구성됨.

외폐쇄근은 때로 대퇴내측그룹으로 간주되기도 하고 제외되기도 함. 

치골근은 대퇴내측구획 그룹으로 간주되기도 하고 제외되기도 함. 

2, 근육 구조양식(muscle architecture)

1) 평행섬유배열(parallel fiber arrangement)

- 5가지 다른 형태가 존재 

- flat,  fusiform, strap, radiate or  convergent, and  circular

 In the parallel fiber arrangement, the fascicles are parallel to the long axis of the muscle. The five different shapes of parallel fiber arrangements are flat,  fusiform, strap, radiate or  convergent, and  circular (Fig. 3-3).

2) 깃털모양의 섬유배열(penniform fiber arrangement)

- unipennate, bipennate, multipennate세가지 형태가 존재함.

근육길이와 근섬유 길이(단면적)

- muscle length and fiber length

- 아래 그림의 상완이두근은 근육길이와 근섬유 길이가 동일함

- 외측광근은 넓은 생리학적인 단면적을 가지므로 큰힘을 낼 수 있음. 그리고 근섬유 길이은 근육길이 보다 짧음 .

- 중둔근은 단면적이 매우 넓음을 보여줌. 

3) 근육의 날개각(pennation angle)

근육 날개각은 근육이 당겨지는 선과 fascicle이 만드는 각도

 The pennation angle  is the angle made by the fascicles and the line of action (pull) of the muscle(Fig. 3-5). The greater the angle of pennation, the smaller the amount of force transmitted to the tendon, and because the pennation angle increases with contraction, the force-producing capabilities will reduce. 

For example, the medial gastrocnemius working at the ankle joint is at a disadvantageous position when the knee is positioned at 90 degrees because of pennation angles of approximately 60 degrees, allowing only half of the force to be applied to the tendon (29). When the pennation angle is low, as with the quadriceps muscles, the pennation angle is not a significant factor.

4) 근육용적과 단면적(muscle volume and cross-section)

- 근육을 단면으로 자르면 근육양(muscle mass), 근육길이(muscle length), 근육날개각 표면은 측정될 수 있음 

- physiological cross-section(PCSA)이 중요함

-  PCSA는 근육이 힘을 생성하는데 직접적인 요소임. 

 The PCSA is directly proportional to the amount of force generated by a muscle. Muscles such as the quadriceps femoris that have a large PCSA and short fibers (low fiber length/muscle length) can generate large forces.

Conversely, muscles such as the hamstrings that have smaller PCSA and long fibers (high fiber length/muscle length) are more suited to developing high velocities. Figure 3-4 illustrates the difference between fiber length, muscle length, and physiological cross-section in fusiform (biceps brachii) and pennate muscles (vastus lateralis and gluteus medius).

5) 근섬유 타입(fiber type)

- 모든 근육은 slow twitch fiber(type1)와 fast twitch fiber(type2)섬유의 조합으로 이루어짐. 

근육노화에 관한 이야기

근섬유의 노화 1. 근섬유 숫자 감소 그리고 motor unit 숫자 감소

근섬유 type의  노화 2. type 2 muscle의 감소

 Each muscle contains a combination of fiber types that are categorized as slow-twitch fibers  (type I) or fast-twitch fibers  (type II). Fast-twitch fibers are further broken down into types IIa and IIb. Fiber type is an important consideration in muscle metabolism and energy consumption, and muscle fiber type is thoroughly studied in exercise physiology. Mechanical differences in the response of slow- and fast twitch muscle fibers warrant an examination of fiber type.

가. slow twitch fiber types

- 지근 섬유는 느린 연축 반응, 타입1 섬유로 근육내 myoglobin이 많아 붉은 색, oxidative

- 느린 수축을 하기 때문에 오랫동안 뛰는데 적합하고, 저강도 일에 적합함. 지구력이 필요한 마라토너의 경우 지근섬유가 많은 비율을 차지함. 

 Slow-twitch, or type I, fibers are oxidative. The fibers are red because of the high content of myoglobin in the muscle. These fibers have slow contraction times and are well suited for prolonged, low intensity work. Endurance athletes usually have a high quantity of slow-twitch fibers.

나. intermdeiate - and fast twitch fiber type

- 빠른 연축반응 섬유, 타입 2섬유

- 타입 2a는 oxidative-glycolytic, red muscle에 가까움. 

- 타입 2b는 glycolytic

 Fast-twitch, or type II, fibers are further broken down into type IIa, oxidative–glycolytic, and type IIb, glycolytic. The type IIa fiber is a red muscle fiber known as the intermediate fast-twitch fiber because it can sustain activity for long periods or contract with a burst of force and then fatigue. The white type IIb fiber provides us with rapid force production and then fatigues quickly.

Most, if not all, muscles contain both fiber types. An example is the vastus lateralis, which is typically half fast twitch and half slow-twitch fibers (31). The fiber type influences how the muscle is trained and developed and what techniques will best suit individuals with specific fiber types. 

For example, sprinters and jumpers usually have great concentrations of fast-twitch fibers. These fiber types are also found in high concentrations in muscles on which these athletes rely, such as the gastrocnemius. On the other hand, distance runners usually have greater concentrations of slow-twitch fibers.

6) 각각의 근육구조(individual muscle structure) - 클릭

The anatomy of a skeletal muscle is presented in Figure 3-6. Each individual muscle usually has a thick central portion,the belly  of the muscle. Some muscles, such as the biceps brachii, have very pronounced bellies, but other muscles, such as the wrist flexors and extensors, have bellies that are

not as apparent.  

골격근은 그림과 같이 근복(muscle belly)이 있는 상완이두근과 같은 근육이 있고, 다른 근육은 근복이 명백하지 않은 경우도 있음. 

Covering the outside of the muscle is another fibrous tissue, the epimysium.  This structure plays a vital role in the transfer of muscular tension to the bone. Tension in the muscle is generated at various sites, and the epimysium transfers the various tensions to the tendon, providing a smooth application of the muscular force to the bone.

근육을 둘러싼 섬유성 막은 근외막임. 근외막은 뼈에 근육장력을 전달하는데 중요한 역할을 수행함. 근육의 장력은 다양한 위치에서 생성되는데, 근외막은 다양한 장력을 건에 전달하여 뼈에 부드러운 적용을 만듬. 

Each muscle contains hundreds to tens of thousands of muscle fibers, which are carefully organized into compartments within the muscle itself. Bundles of muscle fibers are called fascicles.  Each fascicle may contain as many as 200 muscle fibers. A fascicle is covered with a dense connective sheath called the perimysium  that protects the muscle fibers and provides pathways for the nerves and blood vessels. 

각각의 근육에는 수백개에서 수만개의 근섬유(muscle fiber)를 포함함. 근섬유를 둘러싼 띠가 fascicles . 각각의 fascicle은 무려 200개나 되는 근섬유를 포함함. fascicle은 근주막으로 불리는 단단한 결합조직으로 둘러싸여 근섬유를 보호하고, 신경과 혈관을 위한 길을 제공함. 

The connective tissue in the perimysium and the epimysium gives muscle much of its ability to stretch and return to a normal resting length. The perimysium is also the focus of flexibility training because the connective tissue in the muscle can be stretched, allowing the muscle to elongate.

근외막과 근주막내의 결합조직은 근육이 늘어나고 안정길이로 되돌아오게 하는 능력을 제공함.  근주막은 유연성 트레이닝에 초점이 맞추어지는데, 근육내 결합조직이 스트레치될 수 있고, 근육이 늘어나는 것을 허용하기 때문임. 

참고) 근주막의 능동수축에 의한 passive muscle stiffness

The fascicles run parallel to each other. Each fascicle contains the long, cylindrical, threadlike muscle fibers,  the cells of skeletal muscles, where the force is generated. 

Muscle fibers are 10 to 100 cm in width and 15 to 30 cm  in length. 

--> 다른 자료 Muscle fibers can range from 10 to 80 micrometers in diameter and may be up to 35cm long.

fascicle은 서로 평행하게 이어짐. 각각의 fascicle은 길고 관으로 된, 실같은 근섬유를 포함함. 골격근의 세포는 여기서 힘을 생성함. 근섬유는 직경이 10~80 micrometer, 길이는 35cm를 넘기도 함. 

Fibers also run parallel to each other and are covered with a membrane, the endomysium.  The endomysium is a very fine sheath carrying the capillaries and nerves that nourish and innervate each muscle fiber. The vessels and the nerves usually enter in the middle of the muscle and are distributed throughout the muscle by a path through the endomysium. The endomysium also serves as an  insulator for the neurological activity within the muscle.

근섬유는 또한 근내막이라는 막과 평행하게 이어짐. 근내막은 매우 작은 sheath로 미세혈관과 신경을 이어지게 하여 각 근섬유를 영양하고 신경지배함. 미세혈관과 신경은 근섬유 중간으로 들어가 근육에 분포함. 근내막은 근육내에서 신경학적 활성을 위한 절연체임. 

Directly underneath the endomysium is the sarcolemma.  This is a thin plasma membrane surface that branches into the muscle. The neurological innervation of the muscle travels through the sarcolemma and eventually reaches each individual contractile unit by means of a chemical neurotransmission.

근내막의 바로 아래는 근초가 있음. 근초(sarcolenmma)는 얇은 플라스마 막표면으로 근육안으로 연결됨. 근육의 신경학적 지배는 근초를 통하고, 결국은 화학적 신경전달물질을 이용한 수축구조에 도달함. 

At the microscopic level, a fiber can be further broken down into numerous myofibrils.  These delicate rodlike strands run the total length of the muscle and contain the contractile proteins of the muscle. Hundreds or even thousands of myofibrils are in each muscle fiber, and each fiber is filled with 80% myofibrils (5). 

근원섬유는 근육의 총길이를 연결하는 연약한 막대같은 가닥(rodlike strands)이고, 근육의 수축단백질을 함유함. 각각의 근섬유에는 수백 수천개의 근원섬유가 존재함. 근섬유(muscle fiber)은 80%를 근원섬유로 채우고 있음. 

The remainder of the fiber consists of the usual organelles, such as the mitochondria, the sarcoplasm, sarcoplasmic reticulum,  and the t-tubules  (or transverse tubules ). 

근섬유내의 80%근원섬유를 제외한 나머지 성분은 미토콘드리아, 근형질(sarcoplasm), 근소포체(sarcoplasmic reticulum), 평행세관(t-tubules)임. 

Myofibrils are 1 to 2 μm in diameter (about a 4 millionth of an inch wide) and run the length of the muscle fiber (5). Figure 3-7 illustrates muscle myofibrils and some of these organelles. The myofibrils are cross-striated by light and dark filaments placed in an order that forms repeating patterns of bands. The dark banding is the thick protein myosin,  and the light band is a thin polypeptide, actin.  

근원섬유는 직경이 1 to 2 μm이고, 근섬유의 길이와 함께함. 근원섬유는 밝은 필라멘트와 암흑 필라멘트가 cross-striated되어 반복되는 띠형태로 연결되어 있음. 어두운 띠는 두꺼운 단백질 미오신이고, 밝은 띠는 얇은 폴리펩타이드 액틴임. 

One unit of these bands is called a sarcomere.  This structure is the actual contractile unit of the muscle that develops tension. Sarcomeres are in series along a myofibril. That is, sarcomeres form units along the length of the myofibril much like the links in a chain. 

이 띠의 한단위를 근절(sarcomere)라고 함. 근절은 실제로 근육이 수축하는 단위로서 장력을 생성함. 근절이 연결되어 근원섬유가 됨. 근절이 체인처럼 연결되어 길게 연결된 구조가 근원섬유임. 

근육에서 힘의 생성

1. 운동단위(motor unit)

 Skeletal muscle is organized into functional groups called motor units. A motor unit  consists of a group of muscle fibers that are innervated by the same motor neuron. Motor units are discussed in more detail in Chapter 4, but it is important to discuss some aspects in this chapter. Motor units can consist of only a few muscle fibers (e.g., the optic muscles) or may have up to 2000 muscle fibers (e.g., the gastrocnemius). 

골격근은 운동단위라 불리는 기능적 그룹으로 조직화됨. 운동단위는 근섬유의 그룹을 포함하고, 같은 운동신경에 의해서 지배를 받음. 하나의 운동단위는 몇개의 근섬유를 포함할 수도 있고, 2000개가 넘는 근섬유를 포함할 수도 있음. 

The signal to contract that is transmitted from the motor neuron to the muscle is called an action potential.  When a motor neuron is stimulated enough to cause a contraction, all muscle fibers innervated by that motor neuron contract. The size of the action potential and resulting muscle action are proportional to the number of fibers in the motor unit. An increase in output of force from the muscle requires an increase in the number of motor units activated.

운동신경으로부터 근육으로 수축신호가 전달되는 것을 action potential이라 부름. 운동신경 자극이 충분하면 수축을 일으키는데, 하나의 운동신경에 연결된 모든 근육섬유는 수축을 일으킴. 활동전위의 크기와 그 결과로 따라오는 근육활동은 운동단위에서 근섬유 숫자에 비례함. 근육으로부터 발생하는 힘의 증가는 활성화된 운동단위의 숫자의 증가가 필요함. 

2. 근육수축(muscle contraction)

 The action potential from a motor neuron reaches a muscle fiber at a neuromuscular junction  or motor end plate  that lies near the center of the fiber. At this point, a  synapse, or space, exists between the motor neuron and the fiber membrane. When the action potential reaches the synapse, a series of chemical reactions take place, and acetylcholine (ACH) is released. ACH diffuses across the synapse and causes an increase in permeability of the membrane of the fiber. The ACH rapidly breaks down to prevent continuous stimulation of the muscle fiber. The velocity at which the action potential is propagated along the membrane is the conduction velocity.

운동신경으로부터의 활동전위는 신경근접합 또는 운동종판의 근섬유에 도달함. 이 지점에서 시냅스는 운동신경과 근섬유막의 사이에 존재. 활동전위가 시냅스에 도달할때, 연속적으로 화학적 반응이 일어나고, 아세틸콜린이 분비됨. 아세틸콜린이 시냅스를 가로질러 분비되고 근섬유 막의 투과성을 증가시킴. 아세틸콜린은 근섬유의 연속적인 자극을 막기위해 빠르게 분해됨. 

 The muscle resting membrane potential inside is 70 mV to 95mV with respect to the outside. At the threshold

level of the membrane potential (approximately 50mV), a change in potential of the fiber membrane or

sarcolemma occurs. The action potential is characterized by a depolarization  from the resting potential  of the membrane so that the potential becomes positive (approximately 40mV) and is said to overshoot. 

근육의 안정막전위는 바깥쪽과 비교하여 70~95mV임. 

There is a hyperpolarized state (hyperpolarization ) before returning to the resting potential. This is followed by a repolarization,  or a return to the polarized state. The wave of depolarization of the action potential moves

along the nerve until it reaches the muscle fibers, where it spreads to the muscle membrane as calcium ions (Ca2 ) are released into the area surrounding the myofibrils. 

안정막전위로 되돌아오기 전에 과분극이 있음. 과분극은 재분극후를 따르는 것으로 분극상태로 돌아가는 것임. 탈분극의 파형은 신경을 따라 이동하는데, 신경이 지배하고 있는 근섬유까지...

These Ca2  ions promote cross-bridge formation, which results in an interaction between the actin and myosin filaments (see the discussion of sliding filament theory in the next section). 

When the stimulation stops, ions are actively removed from the area surrounding the myofibrils, releasing the

cross-bridges. This process is excitation–contraction coupling  (Fig. 3-8). The calcium ions link action potentials in a muscle fiber to contraction by binding to the filaments  and turning on the interaction of the actin and myosin to start contraction of the sarcomere.

Muscle force production is achieved in two ways. 

근육 힘생성은 두가지 방법으로 성취됨. 

First, muscle force can be increased by recruiting increasingly larger motor units. Initially, during a muscle contraction, smaller motor units are activated. As muscle force increases, more and larger motor units are engaged. This is the size principle (20). 

첫째, 근육힘은 큰 운동단위 동원이 증가하면 힘이 증가. 근육이 수축하는 초기에 좀더 작은 운동단위가 활성화됨. 근육힘이 증가함에 따라 큰 운동단위가 동원됨. 이를 "크기 원리"라고 함. 

Second, a motor unit may be activated at any of several frequencies. A single action potential that activates a fiber will cause the force to increase and decrease. This is referred to as a twitch.  If a second stimulus occurs before the initial twitch has subsided, another twitch builds upon the first. With subsequent high frequency of stimulations, the force continues to build and forms a state called unfused tetanus.  

둘째, 운동단위는 몇가지 빈도수에서 활성화될 수 있음. 단일 활동전위는 힘의 증가와 감소를 야기할 수 있음. 이것은 근 연축과 연관됨. 만약 두번째 자극이 첫번째 연축전에 일어난다면, 다른 연축은 첫번째 연축에 추가로 힘을 생성됨. 이렇게 연속적인 빈도의 자극은 힘을 만들어내고 unfused 강축을 만들어냄. 

Finally, the force builds to a level in which there is no increase in muscle  force. At this point, the force level has reached tetanus.  This scenario is illustrated in Figure 3-9. In a muscle contraction, both size recruitment and frequency of stimulation are simultaneously used to increase muscle force.

근활주설(Sliding Filament Theory)

 How a muscle generates tension has been an area of much research. An explanation of the shortening of the sarcomere has been presented via the sliding filament theory  presented by Huxley (26). This theory is the most widely accepted explanation of muscular contraction but certainly is not the only one. 

근육이 어떻게 장력을 생성하는가에 대한 많은 연구가 되어 왔음. 근절이 짧아지는 것에 대한 설명은 헉슬리에 의한 근활주설을 통해 제시됨. 이 이론은 근수축에 널리 받아들여지는 이론임. 

In the past, muscle contraction was thought, for example, to be similar to the principle of blood clotting, the behavior of India rubber, a chain of circular elastic rings, and a sliding movement caused by opposite electric charges in the different filaments (42).

In Huxley’s sliding filament theory, when calcium is released into the muscle through neurochemical stimulation,

the contracting process begins. The sarcomere contracts as the myosin filament walks along the actin filament, forming cross-bridges between the head of the  myosin and a prepared site on the actin filament. In the contracted state, the actin and myosin filaments overlap along most of their lengths (Fig. 3-10).

헉슬리의 근활주 이론에서 칼슘이 신경화학적 자극을 통해 근육에 도달할때, 근육수축과정은 시작됨. 근절은 마이오신 필라멘트가 액틴 필라멘트를 따라 걷는 것처럼 수축함. 마이오신 head가 액틴 필라멘트의 준비된 부위에 부착되는 cross-bridge 형성을 통해 .. 수축상태에서 액틴과 마이오신 필라멘트는 가장 많이 중첩됨. 

The simultaneous sliding of many thousands of sarcomeres in series changes the length and force of the muscle

(5). The amount of force that can be developed in the muscle is proportional to the number of cross-bridges

formed. The shortening of many sarcomeres, myofibrils, and fibers develops tension running through the muscle

and to the bone at both ends to create a movement.

수많은 근절의 연속적인 슬라이딩은 근육 길이와 힘을 변화시킴. 

근육힘의 양은 액틴과 마이오신의 cross-bridge 형성숫자와 비율적으로 증가함. 

근섬유, 근원섬유, 근절의 짧아짐은 근육을 통해 장력을 형성하고, 결국 뼈에 힘을 전달하여 움직임. 

근육힘의 뼈를 통한 전달

1. 건과 건막(Tendon versus Aponeurosis)

A muscle attaches to bone in one of three ways: directly into the bone, via a tendon,  or via an aponeurosis,  a flat tendon.  These three types of attachments are presented in Figure 3-11. Muscle can attach directly to the periosteum of the bone through fusion between the epimysium and the surface of the bone, such as the  attachment of the trapezius (56).

Muscle can attach via a tendon that is fused with the muscle fascia, such as in the hamstrings, biceps brachii, and flexor carpi radialis. Last, muscle can attach to a bone via a sheath of fibrous tissue known as an aponeurosis seen in the abdominals and the trunk attachment of the latissimus dorsi.

2. 건의 특성

The most common form of attachment, the tendon, transmits the force of the associated muscle to bone. The tendon connects to the muscle at the myotendinous junction, where the muscle fibers are woven in with the collagen fibers of the tendon. Tendons are powerful and carry large loads via connections where fibers perforate the surfaces of bones. Tendons can resist stretch, are flexible, and can turn corners running over cartilage, sesamoid bones, or bursae. Tendons can be arranged in a cord or in strips and can be circular, oval, or flat. Tendons consist of an inelastic bundle of collagen fibers arranged parallel to the direction of the force application of the muscle. Even though the fibers are inelastic, tendons can respond in an elastic fashion through recoiling and the elasticity of connective tissue. Tendons can withstand high tensile forces produced by the muscles, and they exhibit viscoelastic behavior in response to loading. The Achilles tendon has been reported to resist tensile loads to a degree equal to or greater than that of steel of similar dimensions.

The stress–strain response of a tendon is viscoelastic. That is, tendons show a nonlinear response and exhibit

hysteresis. Tendons are relatively stiff and much stronger than other structures. Tendons respond very stiffly when exposed to a high rate of loading. This stiff behavior of tendons is thought to be related to their relatively high collagen content. Tendons are also very resilient and show relatively little hysteresis or energy loss. These

characteristics are necessary to the function of tendons.  Tendons must be stiff and strong enough to transmit

force to bone without deforming much. Also, because of the low hysteresis of tendons, they are capable of storing and releasing elastic strain energy. The differences in the strength and performance characteristics of tendons versus muscles and bones is presented in Figure 3-12.

Tendons and muscles join at myotendinous junctions,  where the actual myofibrils of the muscle fiber join the collagen fibers of the tendon to produce a multilayered interface (62). The tendon connection to the bone consists of fibrocartilage that joins to mineralized fibrocartilage and  then to the lamellar bone. This interface blends with the periosteum and the subchondral bone.

Tendons and muscles work together to absorb or generate tension in the system. Tendons are arranged in series, or in line with the muscles. Consequently, tendons bear the same tension as muscles (46). The mechanical

interaction between muscles and tendons depends on the amount of force that is being applied or generated, the

speed of the muscle action, and the slack in the tendon. Tendons are composed of parallel fibers that are not

perfectly aligned, forming a wavy, crimped appearance. If tension is generated in the muscle fibers while the tendon is slack, there is initial compliance in the tendon as it straightens out. It will begin to recoil or spring back to its initial length (Fig. 3-13). 

As the slack in the tendon is taken up by the recoiling action, the time taken to stretch the tendon causes a delay in the achievement of the required level of tension in the muscle fibers (46). Recoiling of the tendon also reduces the speed at which a muscle may shorten, which in turn increases the load a muscle can support (46). If the tendon is stiff and has no recoil, the tension will be transmitted directly to the muscle fibers, creating higher velocities and decreasing the load the muscle can support. The stiff response in a tendon allows for the development of rapid tensions in the muscle and results in brisk, accurate movements.

The tendon and the muscle are very susceptible to injury if the muscle is contracting as it is being stretched.

An example is the follow-through phase of throwing. Here, the posterior rotator cuff stretches as it contracts to

slow the movement. Another example is the lengthening and contraction of the quadriceps femoris muscle group

during the support phase of running as the center of mass is lowered via knee flexion. The tendon picks up the initial stretch of the relaxed muscle, and if the muscle contracts as it is stretched, the tension increases steeply in both the muscle and tendon (46).

When tension is generated in a tendon at a slow rate, injury is more likely to occur at the tendon–bone junction

than other regions. At a faster rate of tension development, the actual tendon is the more common site of failure (54). For the total muscle–tendon unit, the likely site of injury is the belly of the muscle or the myotendinous junction. Many tendons travel over bony protuberances that reduce some of the tension on the tendon by changing the angle of pull of the muscle and reducing the tension generated in the muscle. Examples of this can be found with the quadriceps femoris muscles and the patella and with the tendons of the hamstrings and the gastrocnemius as they travel over condyles on the femur. Some tendons are covered with synovial sheaths to keep the tendon in place and protect the tendon.

The tension in the tendons also produces the actual ridges and protuberances on bone. The apophyses found

on a bone are developed by tension forces applied to the bone through the tendon (see Chapter 2). This is of interest to physical anthropologists because they can study skeletal remains and make sound predictions about

lifestyle and occupations of a civilization by eval‎uating prominent ridges, size of the trochanters and tuberosities,

and basic size of the specimen.

Muscle Tissue Properties

Irritability

Contractility

Extensibility

Elasticity

Functions of Muscle

Produce Movement

Maintain Postures and Positions

Stabilize Joints

Other Functions

Skeletal Muscle Structure

Physical Organization of Muscle

Force Generation in the Muscle

Motor Unit

Muscle Contraction

Transmission of Muscle Force to Bone

Mechanical Model of Muscle: The

Musculotendinous Unit

Role of Muscle

Origin versus Insertion

Developing Torque

Muscle Role versus Angle of Attachment

Muscle Actions Creating, Opposing, and

Stabilizing Movements

Net Muscle Actions

One- and Two-Joint Muscles

Force–Velocity Relationships in Skeletal

Muscle

Force–Velocity and Muscle Action or Load

Factors Influencing Force and Velocity

Generated by Skeletal Muscle

Strengthening Muscle

Principles of Resistance Training

Training Modalities

Injury to Skeletal Muscle

Cause and Site of Muscle Injury

Preventing Muscle Injury

Inactivity, Injury and Immobilization

Effects on Muscle

Summary

Review Questions

[heoss]

감사합니다.^^

[안찬근(matrix)]

와~ 좋은자료 감사합니다

[문형철]

이제 드디어 근육에 대해서 완전한 이해에 도달했다 ㅎㅎㅎㅎㅎㅎㅎㅎㅎㅎㅎㅎ

[안찬근(matrix)]

교수님의 그 열정.. 대단하네요 ^^*

[09정문권]

<근육>
-특성
흥분성(민감한 반응조직)
수축성(Isometric, concentric, eccentric)
신장성(힘에 반응하여 늘어남)
탄력성(안정길이로 되돌아감)

-골격근의 중요기능 3가지
움직임 생성
관절안정성
신체위치와 자세 유지

-근육의 그룹 : 하나의 근막으로 둘러싸인 구획내 포함된 근육군..
-근육의 구조양식 : 평행, 깃털모양섬유배열
-근육길이와 근섬유 길이(단면적)와의 관계
ex) 상완이두근 : 근육길이 = 근섬유길이
외측광근 : 근육길이 > 근섬유길이 : 큰힘을 낼수있음
-근섬유타입(type1, 2) : 지근, 속근
-근섬유의 구조, 성분

운동단위motor unit, 근수축의 기전, 뼈를통한 근육힘의 전달

[필요충분조건피팅]

감사합니다.