week 5: skeletal muscle structure and function Flashcards
outline the 3 muscle tenodn units
- contractile element
- series elastic element
- parralell elastic element
outline the function of contractile unit?
active force generation
active tension
capacity for tension impacted by
- length
- fibre profile
- CSA
- fasicle length
- (stiffness)
function of series elastic unit
- provides longditudinal energy transfer from CE to PEE
- ‘spring storage’ of energy when muscle is tensed + stretch in SSC
provides passive tension
- stiffness
- compliance
function of parralell elastic unit
- radioal energy transfer
- longditudinal transfer
- provides passive tension, eg. resistance when a muscle is passivley stretched
- will become more stiff when a muscle is at length
describe the difference between structural and nueral determinants of strength
structural: how it is put together
- CSA
- fibre type
- pennation angle
- fasicle length
- tissue quality
nuerological: improves how it is used
- muscle unit firing frequency
- inhibition vs. frequency
- motor unit recruitment
- MU activation of antagonist/ synergists
- MU type
- central/nueral drive
relationship of CSA/ pennation and strength?
- force genration capacity is proportional to PCSA
- increase of pcsa = increase of strength
- increase pennation = increase force (due to angle)
resistance training can
- increase CSA of type 1, but more type 2 muscle fibres (can happen quickley but then stabilise)
- results in a higher fibre pennation which is more relative to the LOP and has higher force production
- therfore higher strength
- growth happens outward from the muscle belly
relationship of fasicle length and strength?
fascile length (number of sacromeres in series) can impact the force:length, and force:velocity
- longer fasicles = greater velocity
- longer fasicles = greater capacity to generate optimal force at larger capacities
- good for rapid large length-excursions of muscles. eg. sprinting, jumping
- ecc training increases FL
- increased ROM of excercise increases FL
muscle fibre type and force relationship?
evidence for shifting fibre types is elated to MHC (muscle heavy chain) expression
- type 2a and 2b/x have largest force production
- conversion form type 2a to 2b is evidenced
- high velocity training has incresed expression for type 2a muscle fibres, and decrease of type 1
- endurance traing shows an increase of type 1
however studies are not strong/long enough
Explain the typical time-course of adaptation of structural vs neural determinants of Strength
early stages of training:
- rapid changes in nueral improvements
intermediate stages of training:
- sturctural adaptations follow
what is the structural-nueral time course of detraining
within days - weeks of no training:
- nueral adaptations decline quickly
weeks-months:
- structural adaptations such as hypertropojhy of bone and muscle degrade
define hypertrophy
- an increae of muscle fibres
- when the rate of protien synthesis exceeds protein breakdown (anabolism>catabolism)
what are the major inputs that can result in hypertrophy?
gene transcription factors
- load changes how our genes are expressed
- up regulates myonuclei and satellite cells
- increases protien synthesis
myofibrils and mitochondria:
- myofibrils increase size and number by 30%
- mitochondria increase size and number by 30%
- increases sarcoplasmic volume and this increases cell size
satellite cells:
- are activated after a mechanical stimmulus
- creation of new myofibres
- tissue repair and growth
anabolic cell signalling:
- drives the hypertrophic response
describe the stucture of the MTJ and how it can be adapted?
the sarcolemma has extensive folding at its end, these folds interdigitate with folds in connective tissue
adaptations:
- increase in length and thickness of invaginations
- increased fibre branching
- increased collagen and structural protien content
- increased cell proliferation
results in:
- increased SA
- increases the attatchment strength
- and there is greater force distribution
the importance of adaptations to tendons?
habitual chronic load leads to:
- increase of tendon dimensions
- increase of CSA in response to loading
- improves load bearing capacity becuase there is less stress of a given force place upon it becuase stress = F/CSA
- also increses tendon stiffness
- which improves the effciency of the MTJ in the SSC
adaptations of concenctric loading during excercise?
- increase in muscle size
- increase of pennation
- increase of strength
- may elicit a central hypertrophic response
- increase fibre area
- but may result in muscle shortening
