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Anatomy Review: Slow and Fast Twitch Muscle Fibers …

Posted: September 7, 2017 at 1:44 am

Without properly functioning muscles the human body would be unable to move. Muscles help to propel us through space, pump our blood, expand and contract our lungs and move nutrients through our body. One aspect of our skeletal muscles is responsible for athletic stamina. Learn about fast and slow twitch muscles, how they can determine whether you would be a better sprinter or marathoner and the role of massage therapy.

There is no getting around it; all body functions that involve movement require muscle activity. It may be as obvious as when we walk, rise from sitting or toss a ball. It may be movement we take for granted such as our heartbeat or in the iris of the eye. Muscles control the movement of food through the digestive system and enable us to breath. Some muscles are used occasionally; some are in constant use, remaining contracted to help the body maintain posture in defiance of gravity. By their very movement and resulting friction, muscle fibers provide the heat that maintains a consistent body temperature as well as assist in the pumping of blood and lymph in and out of cells.

The human body has three types of muscle skeletal, cardiac and smooth. Skeletal muscle is responsible for posture and movement of bones. It also guards the entrances and exits of the digestive, respiratory and urinary tracts. Cardiac muscle is what the heart is made of. Smooth muscle is found in the gut, around the bronchi, within the urinary tract, the reproductive organs and in the walls of the blood vessels. Skeletal muscle moves in response to nerve impulses. Cardiac and smooth muscle fibers respond to changes in local environment, hormone fluctuation, pH balance, ions and temperature among other factors.

Skeletal muscles connect bone to bone with tendonous attachments. When they contract, the bones generally pull closer together or flex. When they are at rest, the bones are further apart or extended. More complicated movements, such as circumduction, supination, pronation or rotation are a combination of flexion and extension, a blending of muscular contraction and relaxation.

Normally the muscles act together in a coordinated manner, producing smooth, efficient movements. Some movements are under conscious control, especially when first learning specific tasks such as writing or riding a bicycle, other less so like the blinking of eyes or scratching an itch. With disorders such as Parkinsons, the signals from the nervous system to the muscles are confused, producing antagonist and agonistic movements at the same time, resulting in either oscillatory movement (tremors) or persistent spasm (rigidity).

There are two basic categories of skeletal muscle fast twitch (also referred to as fast glycolic or Type IIB) and slow twitch (slow oxidative or Type I). Within the fast twitch there is a second category sometimes referred to as intermediate, Type IIA, or fast oxidative fibers. Each has their own set of characteristics and purpose. The percentage of fast, slow and intermediate twitch muscle fibers varies from person to person. The proportion is determined by genetics but can change with physical conditioning. Certain hormones, such as human growth hormone (HGH), testosterone and thyroid hormones can also stimulate the metabolism and size of muscle fibers.

Fast Twitch (Type IIB):

Slow Twitch (Type I):

Intermediate (Type IIA):

The physiology of fast or slow twitch muscles is most often utilized in sports. Athletes who run provide a good example. Those who spring short distances generally will have a higher percentage of fast twitch muscle fibers, while those who run in marathons have more slow twitch fibers.

Another example often used is the dark and light meat of poultry. The breast muscles or white meat of a free-range chicken consist of fast twitch muscle fibers needed for brief burst of flight, while the red or dark meat in their thighs and legs are used for walking and standing.

The type of skeletal muscle fiber is largely determined by heredity. Massage cant change that. What massage can do is help to bring oxygen and nutrients to muscle cells, which in turn can help them to work more efficiently and heal quicker.

Individuals who are highly athletic or participate in competitive sports have a tendency to test their bodies to maximum endurance and, at the very least, experience sore muscles. They often get injured in their pursuit. Some injuries are serious others are minor, involving microscopic tears in muscle tissue. When administering massage, care needs to be taken to customize the session to the athlete as well as the sport. Sports massage techniques, most of which are derived from traditional Swedish massage, have been found to be the most effective in promoting healing and maintaining optimal fitness.

To maximize the effectiveness of your massage, make sure to ask your clients about any physical training they participate in, whether it be recreationally or professionally. Knowing this may help you determine just which massage techniques will be best for them.

Advanced Anatomy & PhysiologyCommon Sports InjuriesSports MassageSwedish Massage for ProfessionalsUnderstanding Sports Massage

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Premkumar, Kalyani. (2004). The Massage Connection: Anatomy and Physiology, 2nd ed. Baltimore: Lippincott Williams & Wilkins.

Robson, David. How Do Fast-Twitch & Slow-Twitch Muscle Fibers Influence Athletic Performance?. Available from Internet; accessed 25 March 2010.

Wikimedia Foundation, Inc. Muscle. Wikipedia. Available from Internet; accessed 25 March 2010.

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Anatomy Review: Slow and Fast Twitch Muscle Fibers …

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