Muscle Fiber Types PSK 4U North Grenville DHS Mr. S. Kelly Slow - - PowerPoint PPT Presentation

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Muscle Fiber Types PSK 4U North Grenville DHS Mr. S. Kelly Slow - - PowerPoint PPT Presentation

Muscle Fiber Types PSK 4U North Grenville DHS Mr. S. Kelly Slow Twitch Muscle Fibers Darker (red) in colour Contract and relax relatively slowly Able to maintain low(er) tension for a longer period of time Low levels of


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Muscle Fiber Types

PSK 4U North Grenville DHS – Mr. S. Kelly

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Slow Twitch Muscle Fibers

  • Darker (red) in colour
  • Contract and relax relatively slowly
  • Able to maintain low(er) tension for a longer

period of time

  • Low levels of glycolytic enzymes
  • High levels of oxidative enzymes
  • Low levels of myosin ATPase (used to provide

instant energy for muscle contractions)

  • Most active in endurance sports
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Fast Twitch Muscle Fibers

  • More pale in colour
  • Ability to contract and relax quickly
  • High tension over short time period
  • High levels of myosin ATPase
  • Activate 2x or 3x faster than ST fibres
  • Most active in power sports
  • Question: are turkeys walkers or fliers?

Without seeing a live one, how would you know?

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The Muscle Biopsy

  • Used to determine muscle fibre type
  • 1. Injection of local anesthetic into the muscle being

sampled

  • 2. Incision of approximately 5-7mm is made in the skin

and fascia of the muscle

  • 3. The piece of tissue (250-300mg) removed via the

biopsy needle and is imbedded in a compound

  • 4. The sample is frozen in isopentane cooled to –180C
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Application of The Muscle Biopsy

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Why does muscle fiber type matter?

  • Most research suggests sport performance is

due more to genetics (how we’re built) than genetics + training

  • Generally: endurance training can help FT

fibers and strength training can make ST fibers stronger but NOT switch

  • Exception: when some spinal nerves are

severed, fibers revert to FT

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Determinant Method 1: Muscle Histochemistry

  • The biopsy samples are first sectioned (8-10 μm

thickness)

  • Sections are processed for myosin ATPase:

Fast twitch fibres – rich in myosin ATPase (alkaline labile → inactivated or destroyed by high pH conditions) Slow twitch fibres – low in myosin ATPase (acid labile → inactivated or destroyed by low pH conditions)

  • Staining the of the muscle fibres indicates

difference in myosin ATPase concentration

  • Sections are processed for other metabolic

characteristics

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Myosin ATPase

  • Enzyme used for breaking down ATP to fuel

muscle contraction

  • Catalyst for:

ATP + H2O → ADP + P **Chemical reaction is for ATP hydrolysis

  • At the cellular level, ATP binding and protein

activity is called the “powerstroke cycle”

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Determinant Method 2: MHC (myosin heavy chain) Isoform Identification

  • Motor protein of thick (myosin) filaments
  • Similar proteins with a similar but not

identical amino acid sequence

  • Site of myosin ATPase interaction
  • Version of myosin heavy chain isoform

determines speed of ATP hydrolysis, indicating type of muscle fibre

  • Multiple muscle fibre types possible in same

muscle.

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Determinant Method 3: Biochemical ID of metabolic enzymes

  • Combines results of muscle histochemistry

with analysis of enzymes involved in energy metabolism

  • Scott et al (2001) used this process to

essentially classify fibres into: I. Fast twitch glycolytic

  • II. Fast twitch oxidative
  • III. Slow twitch oxidative
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Myoglobin (review?)

  • Oxygen storage unit
  • Delivers oxygen to working muscles
  • Muscle fibres with high levels of myoglobin

are designed for endurance activities

  • Muscle fibres with low levels of myoglobin

are designed for power activities (short term)

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Recall Neuromuscular Lesson?

  • Three criteria to determine muscle

structure and function:

  • 1. Transmission of action potential
  • 2. Release of calcium
  • 3. Attachment/detatchment of myosin and

actin filaments

  • Fast-twitch fibres perform these tasks more

quickly and efficiently.

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How does this apply to sports?

  • Soccer (FC Copenhagen) study: fastest

players are desired

  • Problem: fastest players often succumb to

(semi-serious) injury before reaching the highest level of development (overtraining)

  • Solution: LESS training is the proper

prescription for some athletes…

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Type I: Slow Oxidative

  • Generate energy

more slowly

  • More fatigue

resistant

  • Primarily aerobic
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Type IIA: Fast Oxidative-Glycolytic

  • Intermediate type of

fibres

  • High speed energy

release

  • Some glycolytic

capacity

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Type IIB (IIX): Fast Glycolytic

  • Store high levels of

glycogen

  • High levels of enzymes

allowing quick anaerobic contractions

  • Important: training can

transform type IIX fibres to type IIA fibres

  • Type IIA fibres cannot

become Type I fibres

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Tonic Muscles

  • High percentage of Type I fibres
  • Involved in maintaining stability and posture
  • Ex: soleus
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Phasic Muscles

  • Higher percentage of Type II (A and X) fibres
  • Used for powerful movements
  • Low conc of Type I fibres
  • Ex: quadriceps
  • NOTE: a muscle biopsy (see previous) can

determine the ratio of fast- to slow-twitch muscle fibres

  • FT (IIB) fibers contract about twice as fast as

ST

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Questions and Application

  • Why is it important to know (even roughly) the

ratio of FT to ST muscle fibres in an athlete?

  • How can this knowledge translate to greater

success?

  • Does an athlete need to know this information?

Would it help if he or she had this knowledge? Why (not)?

  • Think of a specific example or situation where

this information would be important from an athletic training standpoint