Flashcards in Muscle Mechanics Deck (26)
Do isometric contractions do work or have power?
They do no work and have no power
How is an isometric contraction described?
This is when a muscle develops tension but stays the same length (because the ends are attached to immovable objects)
Why does an isometric contraction do no work?
Because W= F(l). Since the muscle is attached to immovable objects at either end, it cannot change its length....therefore W=0
What are isometric contractions involved in?
In an isometric twitch, what offsets contractile element contraction so that there is no movement?
Stretching of Series Elastic elements (SE)
When the contractile element of a muscle shortens, what does the series elastic element do to offset that?
It lengthens an equal distance...which leads to an isometric contraction
Body movements require what type of contractions?
Both isometric and isotonic contractions
What type of movement is isotonic contraction associated with?
It is associated with Body movement
Describe isotonic contraction
The length of the muscle changes but the tension in the muscle is sustained.
The force of the contraction is at least equal to the load so that the muscle shortens
Hoe is an isotonic twitch measured?
An isotonic twitch is measured by attaching the muscle to a moveable load
For isotonic contractions, why do tension curves look different?
It depends on the load placed on the muscle....the greater the load, the higher the plateau and the greater the time lag between stimuli and the start of the muscle shortening
What happens if the load exceeds the amount of force the muscle can generate?
An isometric twitch
What is the sequence of events in an isotonic twitch?
1- Actin and myosin are activated and the cycling of cross bridges begins
2- the contractile element shortens
3- series elastic element lengthens
4- Tension builds up to equal or exceed the load
5- Load begins to move
6- Tension becomes constant
7- Contractile element shortens even more
8- Load moves (under constant tension)
Do isotonic contractions do work?
Yes, because W= T(d)
What are the four phases of an isotonic twitch upon stimulation?
1- Isometric tension development
2- Isotonic shortening
3- Isotonic relaxation
4- Isometic relaxation
As the weight of an load of an isotonic twitch increases, what changes are made to the twitch?
1- the initial velocity of shortening decreases (the latent period also increases)
2- the amount of shortening decreases
3- the duration of shortening decreases
What is Po?
This is the maximal isometric tension that can be generated at a given initial length and a given state of contractility
the larger the muscle the larger the Po because the larger number of cross bridges
How can Po increase in skeletal muscle?
1- Increase with frequency of modulation
2- Recruitment of additional motor units
3- Initial lengths close to the optimal initial length
Hoe can Po increase in cardiac muscle?
1- increased initial length
2- increased contractility
When do myofibrils produce maximum work and power?
Can certain types of muscle fibers shorten faster than others?
What is the "preload"?
The load required to stretch a muscle from its resting length (to it operating length)
What is the total load?
The Preload + the Afterload
What is the "afterload" equivalent to?
the afterload is equivalent to the total tension
How are length-tension curves produced for isometric contraction?
They are produced by measuring the maximum tension that can be developed during an isometric twitch at varied lengths