single-fibre and whole-muscle mechanisms Flashcards
what is tension
The force that a muscle exerts
on the joint when it is contracting is
called the tension of the muscle.
what is the load
The force that is exerted on a
muscle by an object is called the load of
the muscle.
what is the relationship between tension and load
Muscle tension must exceed the load in order for the muscle fibres to shorten, and
therefore move the object that is responsible for the load.
If muscle tension does not exceed the load then the muscle will either remain at
the same length, or it will lengthen.
what is a concentric contraction
SHORTENING CONTRACTION (concentric contraction)
➢Constant load, muscle shortens
➢Tension > load
what is an isometric contraction
Constant muscle length
* Free object: load = tension
* Fixed object: load => tension
what is an eccentric contraction
- LENGTHENING CONTRACTION (eccentric contraction)
➢Muscle length increases
➢load > tension
what is a twitch
The mechanical response of a
muscle fibre to a single action
potential
what is the latent period
After the action potential, there is a
latent period(few milliseconds)
before the tension in the muscle
fibre begins to increase.
what is the contraction time
The time interval from the beginning
of tension development (at the end
of the latent period) to the peak
tension is the contraction time.
in a concentric contraction increasing the load will cause
- The latent period to increase
- The velocity of shortening to slow down
- The total duration of the twitch to become shorter
- The distance shortened to become less
concentric contraction with the absence of load
a shortening contraction
reaches its maximum shortening velocity
* When the load increases to the point where the
muscle is not able to move it, then the contraction
becomes isometric
* When the load increases beyond the peak tension
that a muscle can produce, the contraction becomes
lengthening (eccentric)
what is summation
The increase of muscle tension from successive action potentials
what happens if you narrow the twitch times
you will get a larger and much longer duration of tension produced
what is tetanus
when successive stimulation result in a sustained contraction
what is unfsued tetanus
the muscle fiber has time to partial relax before the next stimulation, the tension then oscilliates
what is fused tetanus
the muscle fiber has no time to relax
length tension relationship
the shorter the muscle fiber leads to less cross bridges due to an overlap, the muscle can no longer shorten meaning their is less tension produced
at the optimal/ resting lengthen of the muscle their is maximal tension produced
at the muscle lengthened completely will produce lower tension due to cross bridges cant go together due to the distance between them
what is passive tension
tension relased when the muscles starts to lengthen
what are the 3 characters that differ between muscle fibers
- Primary mechanisms used to produce ATP
- Type of motor neuron innervation
- Type of myosin heavy chain expressed
what are the 3 muscle fiber types
- IIx: Fast-twitch, fast-glycolytic fibres
- IIa: Intermediate fibres, fast-oxidative glycolytic fibres
- I: Slow-twitch, slow-oxidative fibres
differences in slow twitch and fast twitch fibers
oxidative are red/black coloured aswell as surroned by mitrocondria
fast glycolic has a higher surface area
muscle fiber differences
- On average 45 –55% type I fibres in arm and
leg muscles - No gender differences in fibre distribution
- Large intra-individual variation
- Trend in distribution consistent across
muscle groups
muscle fiber: production of ATP
Slow oxidative fibres:
Low ATPase activity, highly oxidative
Fast oxidative fibres:
High ATPase activity, highly
oxidative/moderately glycolytic
Fast glycolytic fibres:
High ATPase activity, highly
glycolytic
what influences muscle contraction speed
- Muscle contraction speed (shortening velocity) depends on the rate
of cross bridge cycling(calcium cycling) - … which depends on the myosin heavy chain isoform
- Shortening results in changes in the I band but not the A band
what mechanisms are involved with muscle fatigue
1.CONDUCTION FAILURE Caused by potassium accumulation in
the T-tubules Fast recovery
2.LACTIC ACID BUILDUP Acidic environment in muscle affects the
physiological functioning of proteins and the mechanisms involved in calcium release and re-uptake
3.INHIBITION OF CROSS-BRIDGE CYCLING Accumulation of ADP and Pi in muscle fibres slows down the cross-bridge cycling by preventing the release of cross-bridges from actin molecules
4.FUEL SUBSTRATES Muscle glycogen, blood glucose, dehydration.
5.CENTRAL COMMAND FATIGUE Failure to propagate signals from
the brain to the motor neurons
what are the techniques to determine fiber type
Colour of fibre (~1900)
* EMG identification of motor units (~1950)
* Fibre speed and oxidative capacity (~1970)
* Myosin heavy chain isoform (~1990)
* Genomic nomenclature (~2000)
Gene expression e.g. slow / fast contractile speed families,
mitochondrial gene families
