Muscle Mechanics 1 Flashcards
What are isometric contractions? Do they produce work and power?
When a muscle stays the same length but produces tension. It does no Work and has no power.
What physiological processes involve isometric contractions?
They are involved in maintaining posture.
Explain the series elastic element (SE) and the contractile element (CE) and how they interact. Is this type of movement isometric or isotonic?
During the development of tension the degree of shortening of the CE equals the degree of elongation of the SE thereby keeping the overall length of the muscle fiber constant. It is isometric.
Do body movements use isometric, isotonic, or both?
Most coordinated movements of the body involve a combination of isotonic contractions in some muscles and isometric contrition in other muscles. (ie. heavier load needs isometric but to life the load isotonic is needed)
Define an isotonic twitch and describe the graph of a curve
When the force of contraction of the muscle is at least equal to the load so that the muscle shortens. The tension curve shows a plateau during which the force or tension is constant.
What happens if a load exceeds the amount of force the muscle can generate?
An isometric twitch results
What effect does placing a greater load have on an isotonic twitch?
The greater the load the higher the plateau and the greater the time lag between the stimuli and the start of muscle shortening.
What happens to the tension once an object begins to be lifted?
The tension becomes constant when the load is lifted resulting in a smooth constant velocity lift. The contraction is isotonic during shortening.
What are the 4 stages of an isotonic twitch?
1-isometric tension development (T develops w/o shortening until the F=load)
2-isotonic shortening
3-isotonic relaxation
4-isometric relaxation (reduction of tension at Li)
What are the effects of isotonic twitches with heavier loads?
Latency until shortening increases. Initial velocity of shortening decreases. (Distance of shortening decreases) Duration of shortening decreases.
Why does a muscle lift a heavier load mor slowly than a lighter load?
Mor of the cross-bridges are needed to maintain tension against a heavier load so less are available for shortening.
Why does a muscle lift a heavier load less high than a lighter load?
At a slower velocity with a heavier weight the muscle will shorten less before relaxation occurs
Why does the muscle hold a heavier weight for less time than a lighter load?
Re-accumulation of Ca into the SR causes the tension to be less than the load sooner; hence, the weight is dropped sooner
When does maximum velocity occur for an isotonic twitch? What is it a function of?
It is extrapolated to a zero load and is maximal when there is no load. It is a function of myosin ATPase in varying muscle types (slow, fast)
What is Po and what is it a function of?
Po is the maximal isometric tension that can be generated at a given initial length (it is dependent on Li) and is a given state of contractility. Po is a function of the number of force-generating cross-bridges that can be formed.
