CHAPTER 11: ECCENTRIC

Question 1

Eccentric Contraction Definition

Answer 1

The stretching of a muscle in response to an opposing force on that muscle, in which the opposing force (weight being lifted) is greater than its current force produced

Question 2

Describe what happens to the myofilaments and cross bridges during eccentric contraction

Answer 2

when myofilaments of muscle fibre are stretched during contracting, there may be a decreased rate of cross-bridge detachments (therefore an increased percentage of cross-bridges remain attached) leading to a greater force production on the eccentric bout

Question 3

Describe what happens to titin during eccentric contraction

Answer 3

there is an increase in stiffness of titan protein, titan adds a passive force enhancement to the muscles force production while being lengthened (under load)

Question 4

Describe what happens to the sarcomere during eccentric contraction

Answer 4

eccentric actions place a stretch on the sarcomere to the point where the myofilaments may experience sarcomere strain, or damaged, referred to as exercise induced delayed onset of muscle soreness (DOMS)

Question 5

why do eccentric contractions generate more force than concentric contractions?

Answer 5

1. Generates greater tension with a smaller percentage of available cross-bridges because:
   - an increased PERCENTAGE of cross bridges remain attached in a strong binding position, leading to greater force production.
   - muscles fibres are still recruited asynchronously, but a percentage remain attached, whereas in concentric contraction, only asynchronous cross bridge formation occurs
2. Elastic properties of muscles and tendons contributes to passive force, there is an increase in stiffness of the titin protein during eccentric contraction
3. more muscle damage results in greater repair required, muscles become stronger
   - during eccentric contraction, more damage, less cross bridges attached, greater tension per fiber

Question 6

Exercise-induced muscle damage and soreness

Answer 6

• eccentric contraction requires fewer muscle fibres to generate same force as concentric contraction
• eccentric movement generates greater tension per fiber, more muscle damage
• muscle damage affects fast twitch fibres more than slow twitch, because you engage your fast filers to create a lot of tension whilevonly using a few cross bridges

Question 7

Advantages of Eccentric training

Answer 7

1. Eccentric training requires 80% less oxygen than concentric work and improves muscle work economy by up to 50%.
2. The body can resist 30-40% more weight eccentrically, allowing for training with heavier weights and quicker progress.
3. Eccentric exercises feel easier due to less oxygen use and perceived exertion, enabling higher force output and more training.
4. Eccentric training enhances concentric abilities and promotes muscle growth and strength through more muscle damage.
5. High-load eccentric training delivers significant physiological benefits and improves performance in activities like jumping and deceleration.

Question 8

differences in lactate production in eccentric and concentric contraction

Answer 8

Eccentric exercises recruit fewer muscle fibers than concentric exercises for the same workload, resulting in lower lactate production.
-there is less ATP demand for cross-bridge cycling, leading to less glucose breakdown and lower lactate production.
-

Question 9

Cause of Muscle Soreness

Answer 9

due to micro trauma from eccentric contractions, not lactate accumulation, as lactate is cleared from the bloodstream rapidly.Lactate levels return to resting value quickly after exercise, but muscle soreness (DOMS) peaks much later (48-72 hours).

Question 10

Benefits of chronic eccentric training

Answer 10

Characteristics :

1) Absorption of energy - can absorb more energy
2) High muscle forces - generates high level of force
3) Low metabolic requirement - low demand on cardiovascular system (lungs and heart)

Functional consequences

1) Stiffer muscle spring - muscles become stiffer and act as a spring, storing and releasing energy efficiently
2) Increased muscle size and strength - hypertrophy

Applications

1) performance sport - Improves sport performance
2) Rehabilitation - improves recovery from injuries

Question 11

Inactivity

Answer 11

1. protein synthesis decreases after 6 hours of inactivity
2. noticeable atrophy within 3-4 days
3. greater with immobilisation and weightlessness
4. muscle weakness + fatigue levels may exceed atrophy

Question 12

Age-related changes in skeletal muscle

Answer 12

sarcopenia = loss of muscle mass due to ageing

• 10% muscle mass lost between ages 25–50 years (if not physically active)
• Additional 40% lost between ages 50–80 years
• Loss of fast fibers; gain in slow fibers
• Fewer motor units, Also due to reduced physical activity
• Regular exercise can improve strength and endurance
• cannot completely eliminate the age-related loss of muscle mass ( sarcopenia)

Question 13

Magnetic resonance imaging (MRI) cross-sectional areas (CSA) of thigh muscles

Answer 13

1. older people often have thinner muscles and more subcutaneous fat in their limbs
2. due to decreased levels of physical activity
3. prevent through resistive training and physical activity