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 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

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?

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

Application of The Muscle Biopsy

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

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

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”

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.

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

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)

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.

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…

Type I: Slow Oxidative

• Generate energy

more slowly

• More fatigue

resistant

• Primarily aerobic

Type IIA: Fast Oxidative-Glycolytic

• Intermediate type of

fibres

• High speed energy

release

• Some glycolytic

capacity

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

Tonic Muscles

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

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

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