Section 7: Force of Contraction & Muscle Fiber Types

Force depends on ____, which is affected by

number of cross bridges attached

1. number of muscle fibers stimulated - recruitment

2. Size of fiber (hypertrophy increase strength)

3. Stimulation frequency

4. Degree of muscle stretch

Length tension relationship

Muscle fibers at 80-120% normal resting length → more force

Too short - excessive overlap → less force

Too long - not enough overlap → less force

what affects Velocity and Duration of Contraction (3 things)

Muscle fiber type (fast or slow)

load (greater load less contraction)

recruitment ( more motor units contracting, faster and longer contraction)

Influence of load

Greater load, greater latent period, slower contraction and shorter duration of contraction

Three types of muscle fibers

Slow oxidative fibers, Fast oxidative fibers, Fast glycolytic fibers

Most muscles contain _____ fiber type, all fibers in one motor unit is ____ fiber type, ____ dictates percentage of each

mixture of, same, genetics

Slow oxidative fibers - size

half diameter of fast fibers

what is slow oxidative fibers good for and why

long periods of contraction (marathons)

capillary networks that support oxygen demand

lots of myoglobin (carry oxygen) → aerobic pathway

Fast Glycolytic Fibers - structure

Large diameters with densely packed myofibrils

high glycogen reserves

and few mitochondria

no myoglobin

Fast glycolytic fibers - good for what - how and why

powerful contractions - really short term

Use massive amounts of ATP & fatigue quickly → anaerobic respiration

Fast oxidative fibers

Hybrid of other two

Fast contraction - uses aerobic respiration and some anaerobic respiration

high myoglobin content and some glycogen

Recruitment order

slow oxidative fibers, fast oxidative fibers, fast glycolytic fibers

Which fiber contributes to high contractile velocity

fast glycolytic fibers (fatigable)

which fiber contributes to high contractile duration

slow oxidative fibers (fatigue resistant)

Aerobic exercises

endurance exercises

Running

• Cycling

• Swimming

• Distance sports

aerobic exercise adaptations

more muscle capillaries, mitochondria, myoglobin synthesis

more oxygen and atp production

Could convert fast glycolytic fibers into fast oxidative fibers

What does aerobic exercises improve

endurance, strength, and
resistance to fatigue

Resistance exercise

usually anaerobic

• Weight lifting

• Resistance bands

• Strength training

Resistance exercise adaptations and how

hypertrophy (muscle fiber size increase) → Increased muscle strength
and size

more myofilaments,glycogen stores, and connective tissue

Atrophy and waht are the two types

opposite of hypertrophy

disuse and neurogenic

disuse hypertrophy

from immobilization → muscle strength decline 5% a day

neurogenic hypertrophy

no neural stimulation → ¼ of original size

fibrous connective tissue replace muscle tissue → cant rehibilitate