Week 1 Skeletal muscle plasticity and adaptations to exercise

Question 1

How much of Type I fibers do humans have?

Answer 1

45-55% of Type I fibers

• large inter individual variations but no gender differences
• greatest influence on fiber type is genetics

Question 2

What fiber types do endurance athletes predominantly have? What about sprint athletes?

Answer 2

Endurance: Type I fibers (slow twitch, red) predom.

sprint: Type II fibers (fast twitch, white)
- endurance athletes and weight lifters may demonstrate conversion of Type IIB to IIa fibers (Type IIB-greatest anaerobic potential, Type IIa-aerobic and anaerobic)

Question 3

Describe muscle fiber type adaptations with aging.

Answer 3

• progressiv decrease in number and area of Type II fibers
• 40-50% decrease in muscle mass from fiber atrophy and loss of motor units
• declines in concentric strength slowly at first then rapidly after middle age
• declines in eccentric strength at later age

Question 4

Describe neuromuscular adaptions in enhancing skeletal muscle force production.

Answer 4

• first gains in strength in initial 4-6 weeks of resistance training are primarily due to neuromuscular adaptations (after is hypertrophy)
• accounts for rapid and significant increase in strength early in training, without increase in muscle size and cross sec area
• CNS and psychologic factors important contributors to expression of strength
  1. increase motor unit recruitment
  2. increased firing freq of motor units
  3. increased motor unit synchronization
  4. increased activation of synergist muscles
  5. increased inhibition of antagonist muscles

Question 5

What changes in muscle fiber type proportions and size take place with RT training?

Answer 5

-increase in fiber area but no evidence of increase in proportion of Type II/Type I fibers

Question 6

What changes occur with muscle hypertrophy?

Answer 6

• accelerated protein synthesis
• increased myonuclear number and synthesis of cellular components, particularly protein filaments that constitute contractile elements
• also can result from repeated muscle fiber injury or damage followed by overcompensation of protein synthesis to produce net anabolic effect

Question 7

Delayed onset muscle soreness (DOMS) may be produced by 1 or a combination of the following factors:

Answer 7

1. microscopic tears in muscle tissue or damage to its contractile components with accompanying release of creatine kinase, myoglobin, and troponin I
2. osmotic pressure changes that cause fluid retention into surrounding tissues
3. muscle spasms
4. overstrentching and tearing of muscle’s CT harness
5. acute inflammation
6. alteration in cell’s mechanism for Ca2+ regulation (high Ca levels in cell due to injured muscle fiber, increase free Ca conc., move into cytosol of damaged fiber, autolytic process)

Question 8

What types of contractions result in greater muscle damage and compensatory adaption.

Answer 8

Eccentric>concentric

Question 9

What can improve muscle mass and strength?

Answer 9

1. resistance training-progressive
2. anabolic steroids-androgens
   - effect from increase in protein synthesis and possible inhibition in protein degradation
3. myostatin
   - negative regulator of muscle mass
   - elevated in people with muscle wasting diseases
   - mutation of gene results in decrease in myostatin and increase in skeletal muscle mass