Motor Units
Daily tasks, for instance walking to the bathroom, talking one of your friends or eating the dinner all require multiple muscles that innervate body parts to move properly in order to complete specific tasks. Motor units that consist tens, hundreds or even thousands of motor nerves branches are connected to the muscles. In our body, Rectus femoris contains approximately 1 million muscles fibers which are controlled by around 1000 of motor nerves. Within one motor units which can categorized to type I (slow twitch) or Type II fibers (fast twitch), the composition type of the muscle fiber will be consistent (homogeneous); whereas within one muscle, there will be several different combination of two types of motor units (heterogeneous).
There are three primary types of muscle fibers: Type I, Type IIa and Type IIb. As described above, Type I muscle fibers are known as slow twitch oxidative, Type IIa are fast twitch oxidative and Type IIb are fast twitch glycolytic. These three different types of fibers are specialized to have unique funtionalities. Type I fibers are described as high endurance but low Force/Power/Speed production, Type IIb as low endurance but high Force/Power/Speed production and Type IIa fibers are characterized in between the two.
Motor units are multiple muscle fibers that are bundle together and when an athlete want to move their body to achieve a certain task, the brain then send out a instantaneously impulse signal that reach the specific motor unit through the . After receiving the signal from the brain, the motor unit contract muscle fibers within the group for movement of the body. There are no partially firing in the motor unit which means that once the signal is detected, the muscles contract 100%. However, there are different intensity of activities involve in either daily tasks or athletes competitions that require just the right Force/Power/Speed provide from the muscle. Since the motor unit contracts its fiber 100% once stimulated, types of motor unit that generate variety of Force/Power/Speed are significant.
Fiber Type—Contraction Speed—Time to Peak Power—Fatigue
I (slow twitch)-------slow--------------100 milliseconds--------slowly
IIA (fast twitch)-----fast-----------------50 milliseconds--------fast
IIB (fast twitch)-----very fast-----------25 milliseconds--------fast
Read more about this topic: Motor Control, Motor Control in Athletes
Famous quotes containing the words motor and/or units:
“This biplane is the shape of human flight.
Its name might better be First Motor Kite.”
—Robert Frost (1874–1963)
“Even in harmonious families there is this double life: the group life, which is the one we can observe in our neighbour’s household, and, underneath, another—secret and passionate and intense—which is the real life that stamps the faces and gives character to the voices of our friends. Always in his mind each member of these social units is escaping, running away, trying to break the net which circumstances and his own affections have woven about him.”
—Willa Cather (1873–1947)