Lecture 8 - Force Development & Strength and Power Flashcards
what causes muscle protein synthesis in the muscle (on the cellular level)
Primary messengers
- mechanical stretch (membrane distortion)
- calcium
- ROS (reactive oxygen species)
- phosphorylation potential (AMP:ATP ratio)
ALL OF THE ABOVE WILL ACT ON SECONDARY MESSENGERS P70S6K
what would happen if we removed the P70SK6 second messenger
if we remove this second messenger then the process of muscle protein synthesis will not happen
What is the effect of various exercise intensities (%of 1RM) on hypertrophic gains
rates of protein synthesis at 30% of max RM until failure shows similar results to 80% to failure; with 1RM (just one rep) showed less hypertrophy
what is the combined effect of systemic hormones and resistance training mediated hypertrophy
Post exercise (systemic/natural) increases in hormone levels is not required for hypertrophy/additional muscle strength and MPS to occur
- hormone supplements is a different story
- physiological levels of growth hormone and testosterone have no impact on rate of hypertrophy
how are satelline cells involved in MPS
- muscle fibres are elongated and thousands of nuclei; myonuclei cannot undergo mitosis
- if myofibril area increases, myonuclei-to-cytoplasm volume ratio decreases and could leave to inefficiency within the cell
- satellite cells can undergo mitosis and will be added to the contractile unit to add a new mononuclei to govern an area of myofibril
where are satellite cells located
between the sarcolemma (inner) and basal membrane (outer)
myonuclear domain theory
The myonuclear domain hypothesis dictates that in order to maintain the proper nuclear-to-cytoplasmic ratio, new nuclei are added during hypertrophy and lost with atrophy. myonuclei are added when cross sectional area of muscle increases (~22-26%)
BUT
mononuclei have a long decay life so the muscle could atrophy and lose strength but the nuclei are still gonna be there and would allow you to regain strength faster
- you don’t lose myonuclei to detraining; this is another component of “muscle memory”
primary effect of postexercise hormonal elevations
to increase satellite cell activity as opposed to mediating acute increases in muscle protein synthesis
what is the relationship between size and strength of a muscle
- the size/CSA (cross sectional area) is only part of the process. other factors playing a role in strength are neural patterns, muscle architecture, muscle morphology, etc
- hypertrophy is not nessisarily required for strength gains (consider power vs body builders and muscle fibre density)
besides the increased myofilament content in the muscle, what other adaptations occur during hypertrophy
occur with repeated low load stimuli
increased…
- mitochondrial conc.
- myoglobin conc.
- capillary conc
- sarcoplasmic reticulum conc.
- increased t-tubule conc
- ATP conc.
can only type II fibres hypertrophy
no
- heavy resistance training after extended periods of time can cause a 5-10% type I hypertophy and 15-25% type II hypertrophy
- theres a linear relationship between intensity of loading and hypertrophic rate
costamers
if the number of costameres increases, they will allow for a greater maximal muscle force due to their ability to transfer force longitudinally
- increase number of costameres will decrease shortening speed
neurological factors associated with increased force following training
- maximal activation
- motor unit recruitment
- rate coding - Spinal cord connections
- bilateral limb facilitation?
- motor unit synchronization
- neural excitability - Coordination
- co-activation of antagonist muscle
- improved temporal and spatial motor recruitment
motor unit recruitment and rate coding
The force exerted by a muscle during a voluntary contraction depends on the number of motor units that are activated and the rates at which these motor units discharge action potentials. These two properties are known as recruitment and rate coding, respectively.
- frequency of muscle contraction (rate coding) is dependant on the amount of muscle fibres recruited to contract and produce force. Different types/motor units will change their rate depending on what is needed (see slide 32 for diagram; notice gaps)
is maximal muscle activation really the max
no, the amount of motor units contracting will allow for some units to enter a refractory period while still maintaining the same amount of force
- if all were to contract there would be a refractory period and the amount of force you are able to produce will decrease as all the fibres are fatigued
