aging and rehab of muscle

Question 1

men vs women

Answer 1

Difference in muscle volume and physical strength between men and women continues throughout the life span.

Physical activity also lower in women than men throughout adulthood.

Question 2

muscle vol

Answer 2

peaks at 25 - 35 yrs

Muscle atrophy associated with disuse, reduced number of satellite cells
reduced ability to repair

Question 3

Sarcopenia:

Answer 3

Loss of lean body mass & muscle weakness associated with advancing age

Question 4

Muscle strength predictor

Answer 4

Muscle strength is a strong predictor of: severe mobility limitation, slow gait speed, increased fall risk, risk of hospitalization, and high mortality rate.

older = increase fat, decrease muscle mass

Question 5

The aging-associated loss of muscle mass:

Answer 5

• coincides with the onset of menopause in women
• accelerates during the transition into menopause
• then proceeds slower in women than in men
> 35 years, a healthy person:
• Loses 1%-2% muscle mass per year
• 1.5% annual decline in strength (increases to ~3%
per year @ 60 years)

The age-associated decline in muscle mass affects everyone, even master-athletes

While losing lean body mass, an ‘average’ adult will gain approximately 0.5 kg of fat per year between 30-60 years

The modification in body composition is frequently masked by unchanging body weight
Advanced age (80 yr and older), periods of inactivity, and disease accelerate the process

Question 6

Neural factors that contribute to sarcopenia:

Answer 6

Changes in central nervous system drive (optimising neural drive comes with use/practice)
- Altered neuromuscular junction structure and function (whether changes in the NMJ precede or follow the decline of muscle mass and strength remains unresolved)

Question 7

Neural factors that contribute to sarcopenia:

Answer 7

1. Satellite cells
   - reduced number
   - less responsive ti injury
2. Muscle Fibre
   - decrease in no.
   - decrease in size - predominantly type 2
3. fibre type transformation
   - fast to slow twitch fibre type shift
   (2 > 1 )

Question 8

Neural factors that contribute to sarcopenia: 2

Answer 8

4. Excitation - contraction coupling
   - disruption or uncoupling
   - deficts in calcium release
5. Adipocyte infiltration
6. Mitochondria
   - reduce no
   - loss of enzyme content
7. Myofilaments
   - reduced single fibre max force
   - reduction in myosin protein content and function
   - reduction in elasticity

have motor neuron death

Question 9

satellite cells

Answer 9

• Satellite cells maintain skeletal muscle homeostasis and enable - skeletal muscle regeneration
  Stimulated by damage or stress to muscle tissue
• With aging, muscle tissue homeostasis is progressively disrupted and the ability of muscle stem cells to repair injured muscle markedly declines.

Satellite cells can fuse to form new muscle fibers or self-renew and replenish the satellite cell pool, that will be used in the future

Question 10

Muscle hypertrophy and the 4 stages of the satellite cell cycle

Answer 10

resting myofiber > (myotrauma) satellite activation and proliferation > (can also do self-renewal so goes back to start or) migration to injured fibre > fusion to damaged myofibers (hyperplasia) > regenerated myofiber and added nuclei

Question 11

satellite - 2

Answer 11

age-related decline in satellite cell function compromises recovery capacity of sarcopenic muscles in response to injury
• satellite cell number loss contributes to age- dependent muscle fibrosis (excess fibrous connective tissue)
• Greater reduction of satellite
cells in type II (fast) fibers –
large force, fatigue resistant fibres

Question 12

muscle fibre aging ***

Answer 12

~35% decrease in muscle fiber number between the 20 - 80
- type II muscle fiber myonuclear was only significantly lower in healthy elderly (>70 years) men.”
- The reduction in muscle fiber size is fiber type specific, with 10%–40% smaller type II fibers in elderly compared with young
Type I muscle fiber size is largely unaffected
“… fibrotic tissue replaces the functional muscle”

IF DAMAGED T2 IN AGING, HARDER TO REPAIR

Question 13

motor neurons

Answer 13

Motor neurons die with increasing age

Denervation of type II muscle fibers with collateral re-innervation of type I muscle fiber neurons

Question 14

AGE CHARACTERISTICS

Answer 14

• Young adulthood: intermingling of fibres belonging to different motor units.
  Adulthood to old age: repeating cycles of denervation-reinnervation that result in fibres of the same type being beside one another (fibre type grouping) when viewed in cross-section.

Very old age is characterized by increasing frequency of axonal degeneration and/or motor neuron death leading to grouped fibre atrophy when viewed in cross-section.
- In particular denervation of type II muscle
fibers with collateral re-innervation of type I muscle fiber neurons

Question 15

DECREASE CA2+ RELEASE

Answer 15

• There are receptors in the T-tubule which are needed to activate calcium release from the sarcoplasmic reticulum.
• Once calcium is released, it binds to troponin C and allows actin-myosin cross bridging
• Calcium is then pumped back into the sarcoplasmic reticulum
• Aging is associated with a reduction in # of receptors in the T-tubule and therefore deficits in calcium release
  Structural alterations of myosin (reduction in myosin protein content)
  • Reduces total # actin-myosin cross-bridges
  • Greater % of cross-bridges in a weak- binding state

Question 16

stiffness

Answer 16

With ageing:
An increased in stiffness (reduction in elasticity) has been reported in whole muscle as well as in single fibers.
Altered properties titin

Question 17

Changes in the connective tissue ECM:

Answer 17

• Decreased collagen turnover
• Buildup of collagen crosslinks
• Stiffening of the epimysium

Question 18

altered elasticity

Answer 18

Altered elasticity may expose the collagen of skeletal muscle to deformation or rupturing
Also may alter transmission of tensile muscle force to the tendons

Question 19

Mitochondria

Answer 19

Loss of mitochondrial number Change in morphology and function
Smaller
Reduced oxidative enzymes
(use oxygen to produce ATP)
Mitochondria are the main producer of cellular energy (ATP)
- Lie within the muscle cell
- While # of Type I muscle fibres doesn’t decrease with age, efficiency will due to reduced mitochondrial # & morphology

Question 20

increase fat

Answer 20

• Aging is associated with increases in both intra- and inter-muscular adipose tissue
• Reduced muscle mass is replaced by fat
• Influence pennation angle
• Reduce fascicle length
• Reduced # sarcomeres in series Reduced # cross bridges
• Fat infiltration in skeletal muscle is associated with both metabolic and mobility impairments in older individuals.

Question 21

other difficulties

Answer 21

One of the difficulties in studying the effects of aging is the role that inactivity and injury also play in altering the outcome measures.
- Bed rest and microgravity conditions lead to losses of both myofibrillar and mitochondrial volume
- Likely due to decreased metabolic and mechanical stress on muscle tissue.
2 weeks of immobilization reduces type I, IIa and IIx muscle fibre areas by 13, 10 and 10%, respectively

Question 22

osteoporosis

Answer 22

effect of aging on bone

• decrease BM
• decrease biomechanical properties
• archetecture deterioation

Question 23

Exercise & ageing

Answer 23

Exercise is the primary strategy in the prevention and treatment of sarcopenia.
“The hypertrophic response to exercise training … are similar in young men and women, but
are reduced in older women compared with older men.”

“after muscle-damaging endurance exercise, masters athletes experience slower recovery rates in comparison with younger, similarly trained athletes.”

Progressive resistance training in which the external load is systematically increased as the person is able to work against a heavier load optimises the increase in muscle mass and strength, and attenuates the development of sarcopenia in older people.