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Lectures Nutrition to Support Training Adaptations
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Lectures Nutrition to Support Training Adaptations (HMS4603)1. Muscle
Skeletal Muscle (Function)
4 Main functions of skeletal muscle:
1) Breathing
2) Movement (exercise, performance)
3) Posture ~stability
4) Metabolism (how is protein synthesized etc.)
Skeletal muscle:
- internal motors of human body responsible for all movements of skeletal system
- only have the ability to pull/
shorten (on the joints)
- must cross a joint to create motion
- can shorten up to 70% of resting length
Muscle tendon Model !!
3 components:
1) SEC: Series Elastic Component ( in tendons)
- In series with the contractile component
- Resides in the cross-bridges between the actin and myosin filaments and the
tendons (how strong are these tendons)
2) CC: contractile component (in the sarcomeres)
- Active shortening of muscle through actin-myosin structures
- Sliding filament theory
3) PEC: Parallel elastic component (in the epimysium/perimysium)
- Parallel to the contractile element of muscle
- The connective tissue network residing in the perimysium, epimysium and other
connective tissues which surround the muscle fibers
- Force is basically transferred towards the tendons
Stijn Tans 1
, Stretch-Shortening Cycle:
This determines how you produce and how it’s transported towards the joints
- A quick stretch followed by concentric action in the muscle
- Store energy in elastic structures (SEC & PEC) (e.g. rubber band gets released) à
this results in a (little) higher force production
- Recover energy during concentric phase to produce more force than concentric
muscle action alone
- Examples:
o Vertical jump: counter-movement vs. no counter-movement vs. jump from
standing position (=less high)
o Plyometrics to train these components
Tissue properties of muscle
- Irritability – responds to stimulation by a chemical neurotransmitter (ACh)
- Contractibility – ability to shorten (50-70%), usually limited by joint range of
motion
- Distensibility – ability to stretch or lengthen, corresponds to how much stretch
you can put on the perimysium, epimysium and fascia (=limiting factor towards
agility)
- Elasticity – ability to return to normal state (after lengthening); because the
muscle is returning to its normal state as to where it can produce the optimal
amount of force
Motor Unit
A motor unit is composed of a motor neuron and all of the muscle fibers it innervates
(via the axons)
- Each muscle has many motor units (m.u.)
- # of fibers in a m.u. is dependent of the precision of movement required of that
muscle (average: 100 – 200 fibers/ m.u.) (e.g. finger/face muscle have a lot more
fibers/m.u. compared to your tigh)
o More precision is obtained with more neurons
o 100 to 2000 motor neurons / muscle
- # of m.u.’s in a muscle decreases in the elderly (hence a decline in coordination)
Stijn Tans 2
, !! decrease in m.u. is trainable: e.g. when you start working out your muscle mass
won’t grow at first, but strength will go up. Because the m.u. are training: you get
more neurological input, better coordination of the exercise à this is coming from
the m.u. or add m.u. to an existing muscle
2nd muscle had more precision because of the higher amount of m.u.
Control of tension
- Excitation of each motor unit is an all-or-nothing event (*)
- Increased tension can be accomplished by:
o Increasing the # of stimulated motor units (recruitment)
o Increasing the stimulation rate of the active motor units (rate coding)
(*) : it needs to get to a certain threshold
(of voltage / action-potential) before the muscle shortens itself. This threshold is
different in different muscles, different fibers…
Muscle Fiber Recruitment
T1 (aerobic, slow-twitch) vs. T2 (anaerobic, fast-twitch)
- Each motor unit has a stimulation threshold at which it will begin to produce
force, different fibers are recruited at different stages
- Small motor units (mainly T1) have a lower threshold than large motor unit,
therefore they are recruited first (size principle)
Stijn Tans 3
, !! when doing a 1RM or MVC its mostly T2 that are working, even tough T1 fibers are
also activated as they have a lower threshold. But the T1 fibers aren’t contributing
as much. So during strength training they are working as well, but they aren’t
adapting to the training like the T2 fibers. Same thing for T1 fibers when you run a
marathon for example.
Partly based on ATP production (T2 fibers use glycolysis, while T1 fibers use oxygen)
Rate Coding
A: threshold that needs to be reached for a single twitch
Summation (B in figure) – the overall effect of added stimuli: next contraction starts
when the relaxation phase is not over yet à therefore more force is produced
Tetanus (C in figure) – sustained maximal tension due to high frequency
Stimulation
Stijn Tans 4
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