Lectures 5 & 6: ageing and muscle mass Flashcards
In what unit does the actual skeletomuscle contraction occur?
Sarcomere
Estimated muscle mass loss, after age of 30?
3-8% every 10 years
What are the reasons for muscle mass loss when ageing?
1: Decreased physical activity
2: Decreased anabolic hormones
3: Anabolic resistance
4: Decreased protein intake
TEE: what happens when increasing in age?
when adjusted, it is stable between 20-60 yo
> even during pregnancy
> declines in older adults, to 75% at 100 yo
- Decreased anabolic hormones: which hormones are we talking about?
Testosterone (large person-to-person variation, inreases with resistance training)
Growth hormone (related to sarcopenia, GH therapy might help to increase lean mass)
Insulin: stimulator of AKT MTOR pathway (important in muscle anabolism)
Anabolic resistance: what is it? What are reasons for anabolic resistance?
Attenuated muscle protein synthesis after exercise/amino acid intake
Reasons:
- Reduced blood flow and insulin sensitivity
- Increased splanchnic extraction
- Inflammaging
- Decreased satellite cells (L6)
Explain :Reduced blood flow and insulin sensitivity as a reason for anabolic resistance
Low capillarization of muscle tissue (decreased blood flow) -> amino acids do not reach muscle cells
Explain: Increased splanchnic extraction
as a reason for anabolic resistance
- Uptake of amino acids before they reach bloodstream
- Utilised for gut protein synthesis, or oxidized for energy
- 50% in older adults vs. 23% in younger
Explain Inflammaging as a reason for anabolic resistance
Decrease signalling, beakdown muscle tissue, lower build-up, leads to less muscle mass. Chronic inflammation state
Elderly have a decreased protein intake. How much is needed? How should it be consumed?
Protein division over the day is important. 25-30 gr per main meal to reach anabolic threshold
What is the average gr of protein for dutch people during breakfast?
10 gr average during breakfast, quite low
Expert papers advice to increase intake to ? g/kg (official recommendations Nordic countries)
1.0-1.2
Protein source is important. Quality determined by?
- Amino acid profile
- Digestibility
Feeding: 3 moments during the day, would it help to add another moment of protein intake right before sleep? What does this do?
Yes:
Extra mTOR stimulation
Increases muscle mass
However, accelerates ageing (mTOR)
Balance is important
What decreases faster: muscle mass or muscle strength?
strength
Formula for muscle quality = ?
> Muscle quality = function/mass
What three main types of determinants of muscle quality are there? Examples per types?
Architectural
Capillarization (L7)
Intramuscular fat (L7)
Fiber specific atrophy (= wasting away) (L6)
Satellite cells (L6)
Energetics
Mitochondrial functioning (L7)
Neuromuscular
Decreased voluntary activation
Decreased motor units
Decreased calcium content in muscle fiber
Critical life events: increased catabolic rate during?
- Hospitalisation
- Immobilisation
- Bed rest
- Stressful life events
Bed rest: how much g lean mass lost in young vs elderly?
100 gr vs 600 gr
Hospitalisation: Older adults receiving elective hip replacement: average hospital stay: 5.6 d
average quadriceps volume change:
-3.4%. Being mobile already helps (walking).
What else happens in a hospitalization stay, besides muscle mass loss? in total absence of physical activity?
-> also decrease in insulin sensitivity (-29% after 7 days)
-> no changes in capillary density
Increased inflammation
Muscle protein turnover: what is the same in elderly vs young and what differs?
Breakdown is the same
More synthesis in old vs young, not because of the synthesis an sich, but the response is worse
What can overcome this anabolic resistance ageing effect?
Lifestyle interventions (resistance exercise, physical activity, protein/EAA supplementation) can overcome this ageing effect. Stimulate via amino acids (e.g. leucine; essential, can directly stimulate muscle synthesis)
Fun fact: X months time muscle rebuilt completely. Breakdown and synthesis happening all the time
three
T1 vs T2 fibers: what is the difference?
T1:High mitochondrial content
Abundance of oxidative enzymes
High resistance against fatigue
T2: Including subtypes IIa and IIb
High glycolytic enzyme activity
More prone to fatigue
During ageing something happens with one of the two fibers. Which ones and what happens?
specific loss in type 2 fiber size
No difference in number of fibers!
6-month resistance exercise: Increases quadriceps CSA with 9%. To what fiber(s) can this change be explained?
CSA increase is fully explained by type II hypertrophy
(CSA = cross-sectional area). T2 fiber size can be increased again.
What are satellite cells + what is the function?
Precursors to skeletal muscle cells
Responsible for the ability of muscle tissue to regenerate.
What happens to satellite cells with ageing, illness, disuse?
The number of satellite cells decrease, making them a potential candidate for contribution towards anabolic resistance
What can also happen with ageing with satellite cells, besides decline in number?
Function satellite cells is also diminished with ageing.
They sometimes turn into other cells than fibers (fat cells). Less myotube formation.
Satellite are dependent on what types of environment?
local mirco-environment (niche): younger environment = younger cells
Systemic environment (circulation):
- Parabiosis (connecting a younger organism to an older one: changing its bloodstream) improves satellite cell content
- Inflammation negatively affects SC function
Exercise + protein supplementation prior to surgery helps reduce muscle loss
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