fast-twitch

Examples of fast-twitch in the following topics:

• Slow-Twitch and Fast-Twitch Muscle Fibers

  • Skeletal muscle fibers can be further subdivided into slow and fast-twitch subtypes depending on their metabolism and corresponding action.
  • Fast-twitch fibers are good for rapid movements like jumping or sprinting that require fast muscle contractions of short duration.
  • Unlike slow-twitch fibers, fast twitch-fibers rely on anaerobic respiration (glycolysis alone) to produce two molecules of ATP per molecule of glucose.
  • Muscles controlling eye movements contain high numbers of fast-twitch fibers (~85% fast-twitch).
  • While there is evidence that each person has a unique proportion of fast-twitch versus slow-twitch muscles determined by genetics, more research is required.

• Overview of Motor Integration

  • A motor unit consists of a single alpha motor neuron and all of the corresponding muscle fibers it innervates; all of these fibers will be of the same type (either fast twitch or slow twitch).
  • Time to peak of a twitch contraction (response to a single nerve impulse)
  • The quadriceps muscles contain many thousands of muscle fibers in general, both slow and fast twitch, to produce sufficient force for body movements such as standing, walking, running, and jumping.

• Aerobic Training vs. Strength Training

  • There are two principal ways to categorize muscle fibers: the type of myosin (fast or slow) present, and the degree of oxidative phosphorylation that the fiber undergoes.
  • These slow twitch fibers generate energy for ATP re-synthesis by means of a long-term system of aerobic energy transfer.
  • However, fast twitch fibers also demonstrate a higher capability for electrochemical transmission of action potentials and a rapid level of calcium release and uptake by the sarcoplasmic reticulum.
  • The fast twitch fibers rely on a well-developed, short term, glycolytic system for energy transfer and can contract and develop tension at 2-3 times the rate of slow twitch fibers.
  • Weight lifting involves short, high intensity and high force muscle contractions that utilize anaerobic metabolic pathways to fuel muscle contractions, and prioritizes use of Type II (fast-twitch) muscle fibers.

• Velocity and Duration of Muscle Contraction

  • Skeletal muscle contractions can be broadly separated into twitch and tetanic contractions.
  • In a twitch contraction, a short burst of stimulation causes the muscle to contract, but the duration is so brief that the muscle begins relaxing before reaching peak force.
  • If another contraction occurs before complete relaxation of a muscle twitch, then the next twitch will simply sum onto the previous twitch, a phenomenon called summation.
  • Twitch contractions are short in duration.

• Interactions of Skeletal Muscles

  • Taken all together these three periods are termed a twitch.
  • If an additional action potential were to stimulate a muscle contraction before a previous muscle twitch had completely relaxed then it would sum onto this previous twitch increasing the total amount of tension produced in the muscle.
  • Together these three periods form a single muscle twitch,
  • Repeated twitch contractions, where the previous twitch has not relaxed completely are called a summation.

• Amyotrophic Lateral Sclerosis

  • Other presenting symptoms include muscle fasciculation (twitching), cramping, or stiffness of affected muscles; muscle weakness affecting an arm or a leg; and/or slurred and nasal speech.
  • Symptoms of lower motor neuron degeneration include muscle weakness and atrophy, muscle cramps, and fleeting twitches of muscles that can be seen under the skin (fasciculations).

• Phantom Limb Sensation

  • Phantom limb sensations include pain, itches, twitching, and feelings of gesturing.
  • Although not all phantom limbs are painful, patients will sometimes feel as if they are gesturing, feeling itches, twitching, or even trying to pick up things.

• Muscle Metabolism

  • However, the pool is very small and after a few muscle twitches will be exhausted.

• Postabsorptive State

  • Several metabolic adjustments occur during fasting, and some diagnostic tests are used to determine a fasting state.
  • For example, a person is assumed to be fasting after 8–12 hours.
  • A diagnostic fast refers to prolonged fasting (from 8–72 hours depending on age) conducted under observation for investigation of a problem, usually hypoglycemia.
  • Finally, extended fasting has been recommended as therapy for various conditions by health professionals of most cultures, throughout history, from ancient to modern.
  • During fasting, post-absorptive state, fatty acid oxidation contributes proportionately more to energy expenditure than does carbohydrate oxidation.

• Parathyroid Gland Disorders

  • This can lead to low levels of calcium in the blood, often causing cramping and twitching of muscles or tetany (involuntary muscle contraction), and several other symptoms.