muscular adaptations Flashcards
possible adaptations to endurance training
change in fibre type composition
increased blood supply
increased mitochondria
muscle biopsy
type 1- dark in colour due to high mitochondrial density
type 2- lighter (red)
tybe 2b- white in colour as they use less oxygen and have lower mitochondrial density
hybrid fibres
hybrid fibres also exist which display mixed characteristics of different fibre types- may be in the transition phase
oxidative capacity
1- high
2a- medium
2b- low
glycolytic capacity
1- low
2a- medium
2b- high
mitochondrial density
1- high
2a- medium
2b- low
capillary density
1- high
2a- medium
2b- low
myoglobin content
1- high
2a- medium
2b- low
myoglobin
shuttles o2 from cell membrane to mitochondria
mb has a higher affinity for o2 than hb- even at low po2
allows mb to store o2
myoglobin is what gives muscle (meat) red look
fibre type distribution
% type 1 and 2 fibres not the same throughout the body
typically similar between arms anf legs - may be different in highly trained endurance athletes who use their type 1 muscles more
some exceptions- soleus muscle compised of high % of type 1 fibres in everyone- heavily involved in maintaining upright posture
motor unit
deacribes a motor neuron and all of the muscle cells that it innervates
motor units could be stimulating many or fewer muscle firbres- depending on movement (fine/gross)
motor unit recruitment
all or nothing- when a motor neuron fires all of the fibres that it innervates contract, but the number of motor neurones firing will differ depending on the desired force production
order of recruitment- t1 until fatigue then type 2a then type 2x
progressive recruitment of type 1 followed by type 2a and then type 2b motor units as the intensity of activity increases- explains why fatigue occurs in stages
type 2x fibres are harder to recruit and require increased concious effort to be recruited
sarcomere structure
each myofibril is composed of 1000s of sarcomeres
joined in series and parallel to one another
sarcomeres are functional units of a muscle
made up of myofilaments
myosin
around 300 myosin molecules per thick filament
2 subunits- S1 globular head S2 flexible region and tail
myosin heavy chain isoforms
speed of contraction mainly determines by ATPase
what makes fast twitch fibres fast
rate of ATPase activity is a lot faster in t2 fibres compared to t1, allowing fibres to contract at a faster rate
can we change fibre type
no- proportions are fixed and determined by genetics (partly true)
yes- with endurance training, we can influence fibre type distribution
changing distribution- studies
20 week endurance training programme- 30-50 min of moderate cycling
post training- % of t1 and t2a increased, t2b decreases
sprint training- 4-6 weeks
type 1 decreased
t2a and t2b increased
hybrid fibres have been found and may be as they are in a transition phase- adapting from one type to another
capillaries
site of gas exchange
walls are 1 endothelial cell thick
denser network of capillaries provides a greater SA fir gas exchange
increased capillary density= improved o2 uptake
increased capillary number by >15%
VEGF
vascular endothelial growth factor
VEGF stimulates angiogenesis (blood vessel formation) - signal protein that leads to production of new blood vessels
stimulated by low po2
angiogenesis
development of new blood vessels
training effects
muscle size and capillarisation
more capillaries per muscle fibre in trained athletes
mitochondria
found in cell cytoplasm
major site of ATP production
metabolically active cells have many mitochondria
mitochondrial numbers
study
24 week endurance training programme
classified fibres according to the number of mitochondrial aggregrates seen under the microscope
MA= mitochiondria grouped together inside muscle cell membrane
shows that you can increase number of mitochondria in response to endurance training
