Lecture 34 - Ageing and skeletal muscle Flashcards
What are the multifactorial causes of sarcopenia?
disuse, changing endocrine function, chronic diseases, inflammation, insulin resistance, and nutritional deficiencies
What is the criteria for patients to be considering to be exhibiting sarcopenia?
bedridden, can’t independently rise from a chair
gait speed
What are the 3 criteria that define sarcopenia?
- low muscle mass
- low muscle strength
- low physical performance
Sarcopenia is independent of?
societal factors
ethnicity,
disease states,
income,
health behaviours
drop off is greater for activities that require…
force and power
typically __ muscles are more affected than ___ muscles
typically fast muscles are more affected than slow muscles
What are the factors controlling muscle mass?
Nutritional status hormones genetics innervation inflammation oxidative stress blood flow exercise (activity) Disease protein synthesis/degradation
sarcopenia is a neuromuscle syndrome, meaning…
it is concerning Motor units
there is selective de-innervation of the type to MUs
followed by reinnervation with type 1 MUs
What causes the selective deinnervation of fast MUs?
Two possibilities:
Loss of signals from nerves to muscles
loss of signals from muscles back to nerves
a difficult hypothesis to test - significant interplay between neural and muscular pathways
True of false
with sarcopenia, There is a loss of mosaic pattern of fast and slow fibre distribution
true
fibre type grouping due to selective loss of MUs
Before there is wasting of muscle fibres there are other changed, including:
slowing of contraction
changes in SR - impaired release and reuptake of Ca2+
age-related changes in Ca2+ handling affect speed of contraction
contributes to falls and fall-related injuries (can’t quickly retain balance)
Summarise the motoneuron changes in aging
a loss of motoneurons with aging and a loss of numbers and diameters of motor axons in the ventral roots
some of these cease functioning (fibres may die)
other send out new axonal branches called sprouts
most susceptible MUs are those for the type IIB fibres and this loss of fast-twitch units, not surprisingly, will prolong contraction time
fast fibres reinnervate less successfully than slow fibers
fast fibres remain deinnervated or they are reinnervated by axonal sprouting from slow fibres.
The loss and atrophy of muscle fibres and the remodelling contribute to overall muscle atrophy
possible demyelination could affect NT, slow AP propagation. Other changes to NMJ include:
gradual changes in pre/post synaptic components, incl.
widening of end -plate
longer nerve terminals
fewer side branches
There is an increase in ____ in aging muscle making it more stiff
collagen
what are the changes in skeletal biomechanica variables with ageing muscle?
decrase max running velocity
decrease stride length
decease stride frequency
increase stride cycle time
increase braking and push off contact time
Summarise the cellular and molecular changes that contribute to sarcopenia
muscle fibre satellite cells E-c couplng Adipocyte infiltration mitochonria myofilaments fiber type transformation
muscle fibre
-decrease in number and size (predominately type II)
Satellite cells
- reduced number
- less response to injury
E-c couplng
- disruption/uncoupling
- deficits in Ca2+ release
Adipocyte infiltration
- increase inter and intra muscular adipose tissue
mitochondria
- reduced number
- loss of enzyme content
myofilaments
- reuced single fibre maximal force
- reduction in myosin protein content and function
- reduction in elasticity
fiber type transformation
- fast to slow fibre type shift
what happens to sports performance with ageing?
elite status does not protect msucle from gradual losses in fibres/MUs
loss of power a concern for athletes
injuries are more common
most elite athletes begin to show some decine in performance by their 30s
what are the problems facing older champions?
diminishing muscle mass
progressive decrease in size of type II fobres
declining VO2 MAX
stiffening connective tissue
What can we do to intervene against sarcopenia?
we must attempt to conserve muscle strength for both the prevention and reversal of age-related changes
this can be facilitated by the incorporation of strength training
Strength training in the eldery can be effective at adressing…
increase muscle strength, total body mass and muscle fibre area
significant fibre hypertrophy
true or false
the strength training adaptations in elderly are likely to result from a combination of neural adaptations and muscle hypertrophy
but we must face the fact that loss of msucle mass is inevitable
true
strength training must be a lifelong commitment if it is to be a preventative measure
what are the relevant hormonal changes with ageing
decreased circulating levels of anabolic hormones contribute to changes in muscle size and strength
hormones include: GH, IGF-1, testosterone
compromises efficiency of muscle regeneration as a consequence of daily ‘‘wear and tear’’
what are the therapeutic approaches for combating sarcopenia
exercise - strength training
protein supplements
hormonal - GH, testosterone precursors, selective androgen receptor modulators
true or false
exercise can slow the rate which the sarcopenia changes occur - therefore exercise is very important
true
but there are practical considerations: is high-intensity strength training suitable for most adults, some maybe not.
