2.3 - Muscle Fiber Types

What are the 3 ways muscles generate ATP?

• creatine phosphate

• anaerobic glycolysis

• aerobic respiration

Which of the 3 pathways is very efficient and fast?

creatine phosphate

Creatine phosphate provides:

immediate energy

How long does ATP from CP last?

10-15 seconds

What does CP use?

CP stored in the muscle

Is CP anaerobic?

yes - no oxygen needed

1 creatine =

1 ATP

Anaerobic glycolysis provides:

short-term energy

What does AG break down?

breaks down glucose (from blood) or glycogen (stored in muscle) to product ATP

What does AG generate?

produced ATP and also lactic acid (can lead to muscle fatigue)

How long does ATP from AG provide energy?

30sec to 2 minutes

1 glucose =

2 ATP

Anaerobic =

glycolytic metabolism in sarcoplasm, using glucose or glycogen

Pyruvic acid =

• end product of glucose

• 1 glucose = 2 PA

• if it goes through fermentation, it produced lactic acid

What happens to the pyruvic acid if oxygen is present?

goes into krebs cycle and is converted to acetyl-co-a

Which of the 3 processes has many steps?

Aerobic respiration

Aerobic respiration provides what type of energy?

long-term energy

Where does AR occur?

in the mitochondria - needs oxygen

What at AR use?

glucose, fatty acids, and sometimes proteins to generate ATP

AR provides energy for:

long-duration, low intensity activities

1 glucose = (for AR)

36 ATP

Aerobic =

oxidative metabolism in mitochondria, using pyruvate or acetyl CoA

Products of krebs cycle =

2 ATP, CO2, electrons (will enter the electron transport system)

What does the electron transport system do?

very efficient and can transform the electrons into ATP but oxygen is needed —> this whole system happens in the mitochondria

How many total ATPs are generated between AG & AR?

38

• 2 ATP + pyruvic acid from 1 glucose molecule

• Pyruvic acid = 2 ATPs

• electron transport system = 34 ATPs

What 2 characteristics are used to do muscle fiber typing?

• speed of contractions

• metabolic pathways used to produce ATP

What are the 2 types of muscle fibers?

slow twitch & fast twitch

Type 1 =

slow twitch

Type 2 =

fast twitch

Are all ATP pathways used by each muscle?

yes, but some more than others depending on the muscle type

Type 1: Mitochondria =

high

Type 1: Myoglobin =

high

Type 1: Capillary Density =

high

Type 1: Energy source =

aerobic

Type 1: contraction speed =

slow

Type 1: Fatigue resistance =

high

Type 1: Primary function =

endurance

Type 1: Color =

red

Type 2: Mitochondria =

low

Type 2: Myoglobin =

low

Type 2: Capillary density =

low

Type 2: Energy source =

anaerobic —> type 2a fibers have some aerobic mixed in

Type 2: Contraction Speed =

fast

Type 2: Fatigue resistance =

low

Type 2: Primary function =

short, explosive power

Type 2: Color =

white, or pink for type 2a

Myoglobin = 

iron & oxygen binding protein — mostly in the muscle 

Hemoglobin =

mostly in the blood

What helps type 1 muscle maintain long term?

thicker Z-disk

Poultry leg =

red

Poultry breast muscle =

• white 

• more type 2

• less activities = less oxidative phosphorylation

Muscle close to the bone is:

darker

Pig Semitendinous (eye of round): Color

varying shades of red to white

Pig Semitendinous (eye of round): Superficial portion distribusion

• 80% white

• 20% red

Pig Semitendinous (eye of round): Deep portion distribusion

• 80% red

• 20% white

Muscle stained at a low ph =

• Type 1 = dark

• Type 2 = light

Muscle stained at high pH =

• Type 1 = light

• Type 2 = dark

What is the normal muscle pH?

5-6

Fiber type effects of Obesity & type 2 diabetes?

reduced proportions of type 1 fibers and increased portions of type 2X fibers 

Oxidative fiber =

• Type 1

• Great oxidative enzyme activity, more myoglobin, more redness

• Low glycolytic markers, less glycogen, smaller sarcoplasm = smaller diameter

• Low ATPase activity

• More and larger mitochondria because they are needed for oxidative metabolism

Glycolytic fibers =

• Type 2b

• Low oxidative enzyme activity

• High glycolytic markers, thereby needing more glycogen (storage form of glucose)

• High ATPase activity

Why is Type 1 meat darker?

• Higher myoglobin content

• More mitochondria and capillaries

• Enhanced blood supply

Examples of Type 1 meat:

Beef, chicken thighs, actively used muscles

Why is type 2 meat lighter?

• Lower myoglobin content

• Fewer mitochondria and capillaries

Example of Type 2B meat:

Chicken breast is pale compared to chicken thighs

What are the practical impacts of meat color?

• consumer preference 

• nutritional content 

Why does Type 1 have a higher pH?

• Oxidative metabolism

• Lower glycogen stores

Which type has a slower rate of post-mortem pH decline?

type 1

Why does type 2 have a lower pH?

• Anaerobic glycolysis

• Higher glycogen stores

Which type rapid post-mortem pH decline?

type 2

Practical impacts of meat pH?

• stress management

• chilling rate control

Which type has a higher water holding capacity? Why?

type 1 because higher pH

Practical impacts of water holding capacity?

• meat juiciness

• processing yield

• cooking performance

Meat tenderness depends on:

muscle fiber size & fat, collagen

Why is type 1 more tender meat?

• smaller fiber diameter

• Higher intramuscular fat (lipid) content

• Lower collagen cross-linking

• Thicker Z-lines 

Why is type 2 tougher meat?

• Larger fiber diameter

• Lower lipid content

Practical impact of meat tenderness?

cooking methods

What impacts meat flavor profile?

meat composition

Why does type 1 have more complex flavor?

• Higher intramuscular fat content

• More mitochondria – flavor-enhancing enzymes and phospholipids

• Higher levels of amino acids and nucleotides

• Longer-chain fatty acids

Why does type 2 have less complex flavor?

• Lower intramuscular fat content

• Less mitochondria – flavor-enhancing enzymes and phospholipids

• Fewer fat-soluble flavor compounds

Why does oxidative stability make type 1 have darker meat?

• Higher myoglobin content – pro-oxidant

• More mitochondria - auto-oxidizing membrane phospholipids

• Higher levels of polyunsaturated fatty acids

• Increased iron content – catalyst for oxidation

Why does oxidative stability make type 2 have lighter meat?

• Lower myoglobin content

• Fewer mitochondria

• Higher proportion of saturated fats

• Lower iron content

Practical impacts of oxidative stability?

• storage conditions

• packing conditions