Functions of the Muscular System

Thermoregulation

When body’s heat production is stable, the blood that is flowing into the dermis is regulation depending on changes in ambient temperature. The purpose is to ensure that the difference in temperature between the skin’s surface and the environment remains constant therefore regulating heat loss and maintaining a constant body temperature. When heat production increases, blood flow to the dermis also increases, and therefore increases the heat lost from the skin to the same rate as the excess heat production. An example of this is muscle twitching that creates friction and therefore increasing body temperature.

Movement

There are three planes of movement in which we move, most of our movements are not straight up and down or side-to-side, in sports we combine a mixture of movements in different planes.

Sagittal Plane – passes through your body from front to back, this divides your body in left and right side. Movements in this plane are the up and down movements of flexion and extension.

Frontal Plane – divides the body into 2 parts front and back. Movements in this plane are sideways movements that are known as abduction and adduction.

Transverse Plane – divides the body into 2 parts top and bottom. Movements in this plane are rotational in nature, such as internal and external rotation, pronation and supination.

Flexion and Extension – Flexion is the movement in the sagittal plane; this decreases the angle at the moving joint. Extension is the opposite movement this increases the angle at the joint. There are many types of synovial joint that are capable of flexion and extension, (hinge, ball and socket, saddle, condyloid), including the shoulder, elbow, wrist, hip and knee. Shoulder flexion is the action of raising the arm above the head. Extension is the downward movement. When bending the knee this is called flexion as the angle is reduced and straightening it is called extension.

Flexion and extension at the ankle joint is known as dorsiflexion (when you point your toes towards the ceiling) and plantar flexion (is when you point your toes towards the floor away).

Abduction and Adduction – these movements are involved in the frontal plane and involve moving the body away towards an imaginary centre line. Abduction is taking the body away from the central line and adduction is moving it towards the centre line. Adduction also can be moving the body part across the centre line and to the other side of the body. Another abduction and adduction movements include the fingers. When one moves their fingers apart, this is known as abduction as they are moving away from the centre position. When you bring your fingers back together, this is called adduction, as you are bringing them back to the centre line.

Rotation – movements are in the transverse plane and include any twisting motion. Joints, which allow rotation, include the shoulder and hip. These are known as ball and socket joints. We are also able to rotate our necks and backs this is due to a series of smaller joints for example axial joint which is a pivot joint in the neck between the first two vertebrae. Rotation of the hip and shoulder can be broken into internal or external rotation. An example of internal rotation is the movement of a hand either inwards towards the body or down to point towards the floor. External rotation is the opposite, e.g. when the hand moves away from the body or upwards to the ceiling.

Circumduction – is a combination of all the above movements. This is possible at the ball and socket, condyloid and saddle joints such as the shoulder, hip, wrist and ankle. It involves moving the entire connecting limb through its full range of motion.

Pronation, Supination, Inversion and Eversion – are movements of the forearm and ankle. In the forearm, pronation is the movement of turning the palm over to face downwards. Supination is the opposite movement, of turning the palm up or forwards. Movement here comes from the proximal radio-ulnar joint, which is just below the elbow between the Radius and Ulna bones, which is a pivot joint. This allowing the Radius to move around the Ulna.

Supination in the ankle is the movement of turning the sole of the foot inwards. This is also known as inversion. Pronation is the movement of turning the sole of the foot outwards, also known as eversion.

3 Types of Muscles (Cardiac, Skeletal and Smooth)

Half of your body weight is muscle. In the muscular system, muscle tissue is split into 3 types: skeletal, cardiac and smooth. Each type of muscle tissue in the human body has a unique structure and a specific role. Skeletal muscle moves bone and other structures.

Skeletal Muscles – attach to and move bones by contracting and relaxing in response to messages from the nervous system. Skeletal muscle tissue is composed of long cells called muscle fibers. Muscle fibers are organized into bundles supplied by blood vessels.

Smooth Muscle – is found in the walls of hollow organs throughout the body. Smooth muscle contractions are movements triggered by impulses that travel through the nervous system to the smooth muscle tissue. The cells that lies within smooth muscle tissue allows for contraction and relaxation. Smooth muscle in the walls of organs e.g. urinary bladder and the uterus allow those organs to expand and relax as needed. In the eye smooth muscle changes the shape of the lens to bring objects into focus.

Cardiac Muscle – is found only in the myocardium, contracts in response to signals from the cardiac conduction system to make the heart beat. Cardiac muscle is made from cells known as cardiocytes. Cardiocytes are branched, allowing them to connect with several other cardiocytes, forming a network that facilities coordinated contraction.

Muscle Roles

Agonist – in a movement is the muscle that provides major force to complete the movement. Agonists are known as ‘prime movers’. The bicep curl produces flexion at the elbow; the biceps muscle is the agonist. However the agonist is not always the muscle that is shortening. In a bicep curl the bicep is the agonist on the way up when it contracts, and on the way down when it contracts eccentrically.

Antagonist – in a movement refers to the muscles that oppose the agonist. During elbow flexion where the bicep is the agonist, the tricep muscle is the antagonist. Whilst the agonist contracts causing the movement to occur, the antagonist typically relaxes. However the antagonist doesn’t always relax, another function of antagonist muscles can be presented in a slow or stop movement. The above would be noticed is the weight in the bicep curl was very heavy, when the weight was being lowered from the top position the antagonist tricep muscle would therefore produce a sufficient amount of tension therefore helping control movement as the weight lowers.

Also this helps to make certain that the gravity doesn’t quicken the movement, causing damage to the elbow joint at the bottom of the movement. When the elbow extends against gravity such as in a push-up, bench press and a tricep pushdown, the tricep becomes the agonist and the bicep becomes the antagonist.

Synergist – in a movement is the muscle that stabilizes a joint around the movement occurring, which in turn helps the agonist function effectively. Synergist muscles helps to create movement. In the bicep curl the synergist muscles are the brachioradialis and brachialis, which help the biceps, create the movement and stabilize the elbow joint.

Fixator – in a movement is the muscle that stabilizes the origin of the agonist and the joint that the origin spans in order to help the agonist function. In the bicep curl this would be the rotator cuff muscle, also known as the ‘guardians of the shoulder joint’. Most of the fixator muscles are found working around the hip and shoulder joints.

Types of Muscle Contraction

Isotonic Contractions – cause the muscle to change length as it contacts and causes movement of a body part. There are 2 types of Isotonic Contraction:

·      Concentric – cause the muscle to shorten as it contracts. For example bending the elbow from straight to fully flexed, causing a concentric contraction of the Biceps Brachii muscle. Concentric contractions are the most common type of muscle contraction and occur frequently in daily and sporting activities.

·      Eccentric – are opposite of concentric and occur when the muscle lengthens as it contracts. This involved the control of a movement being initiated by the eccentric muscles agonist. An example of this would when kicking a football, here the Quadriceps muscle contract to straighten the knee and the Hamstrings contract to decelerate the motion of the lower limb.  This type of contraction is commonly involved in muscle injuries.

Isometric Contractions – occur when there is no change in the length of the contracting muscle. An example of this is when you grip something, such as a tennis racket. There is no movement that occur in the joints of the hand, however the muscles are contracting to therefore provide a force sufficient enough to keep a steady hold on the racket. Each muscle has an optimum length at which the maximum isometric fore can be produced. The amount of force a muscle gives during an isometric contraction depends on the length of the muscle at a point of contraction.

Isokinetic Contractions – are similar to the isotonic in that the muscle changes length during the contraction, where they differ is that Isokinetic contractions produce movements of constant speed. In order to measure Isokinetic Dynamometer is required. Isokinetic contraction in day-to-day and sporting event are rare. A good example is breaststroke in swimming; here the water provides a constant, resistance to the movement of adduction.

Different Muscle Fiber Types 

Type 1 – fibers are also known as slow twitch fibers. They are red in colour this is due to the presence of large volumes of myoglobin and therefore the oxygen and high numbers of Mitochondria. Due to this they are very resistant to fatigue and are able to produce repeated low-level contractions by producing large amounts of ATP through an aerobic metabolic cycle. The muscle containing mainly type 1 fibers are often postural muscles such as those in the neck and spine due to their endurance capabilities. Another example of this are the athlete such as marathon runners that have a high number of this type of fiber, through genetics and training.

Type 2a – fibers are also known as fast oxidative fibers and are a hybrid of type 1 and 2 fibers. These fibers contain a large amount of mitochondria and myoglobin, hence their red colour. They make and split ATP at a fast rate by using both aerobic and anaerobic metabolism and therefore produce fast, strong muscle contractions even though they are prone to fatigue than type 1 fibers. Resistance training can change type 2b fibers into type 2a due to a increase in ability to use the oxidative cycle.

Type 2b – also known as fast glycolytic fibers, they have a low level of myoglobin and also contain few mitochondria hence why they are white in colour.  They produce ATP at a slow rate by anaerobic metabolism and break it down very quickly. This then resulting in short, fast bursts of power and rapid fatigue. This type of fiber can be turned into type 2a fibers by resistance training. This resulting in a positive change due to the increased fatigue resistance of type 2a fibers. 

Muscle Movement

Sporting Action	Name of bone that make up the joint (Humerus, Ulna, Radius)	Name and type of Joint (s) involved (i.e. Ball and Socket)	Name of muscles working (i.e. bicep/tricep)	Roles of muscles (i.e. agonist/antagonist)	Type of movement (i.e. Flexion/ Extention)	Type of contractions (concentric / eccentric)
Rugby Kick	- Femur - Fibia - Tibia	- Ball and Socket at the hip joint	- Quad - Hamstring	- Quad – Agonist - Hamstring - Antagonist	- Flextion and Extention	- Hamstring – Concentric - Quad - Eccentric
Gymnastics	- Humerus - Ulna - Radius	- Ball and Socket	- Biceps - Triceps	- Biceps – Agonist - Triceps - Antagonist	- Flextion and Extention	- Biceps – Eccentric - Triceps - Concentric