Contractile Character of Muscle and Fatigue Flashcards
What is an isometric contraction?
Contraction generating force without shortening
What is an isotonic contraction?
Change in length of the muscle fiber to generate force
What is a concentric contraction?
Shortening contraction
What is an eccentric contraction?
Lengthening contraction
What four factors determine the contractile characteristic of muscles?
Duration of active state
Force-velocity relation
Length-tension relation
Fatigability
What is the latent period?
When stimulated muscle processes are underway
Is isotonic or isometric latent period longer?
Isotonic
Why is the isotonic latent period longer?
Because it has to reduce the slack of tendons and elastic fibers from muscle
What is contraction time?
Time to peak tension
What is relaxation time?
Time to required for decay of the active state; determined by rate calcium returns to SR
What is described by the length-tension relationship?
Muscles at different lengths stimulated will give different tension values
What is described by the force-velocity relationship?
A loaded muscle will have a slower contraction velocity than a completely free muscle
What causes the force-velocity relationship?
Cross-bridges maintaining the length can not contract; at lesser loads some CBs are left over to shorten the muscle at a slower velocity
What is the ratio of ATP cost for one AP in type I vs type II muscle fibers?
1:3
Why are FT muscles more costly?
Because they have much faster cross-bridge cycling
What does the Henneman size principle state?
That motor units are activated in a fixed order
Which size motor neurons are activated first?
Smaller motor neurons (Type I)
What is a strong predictor of energy cost during walking?
The vertical displacement of the pelvis
Why is speed decreased in amputees and obese patients?
Because the energy expenditure is greater so they must slow down to conserve energy; still use more energy when moving slower
What is muscle fatigue?
Inability to generate a required force
What are the two types of muscle fatigue?
Central and peripheral fatigue
What is central fatigue?
Fatigue that occurs within the CNS to NMJ
What is peripheral fatigue?
Fatigue that occurs from the NMJ to contractile force generating apparatus
What can contribute to muscle fatigue?
Hydrogen ion conc. from lactate ion
At what concentration of lactate does muscle fatigue typically occur?
18 mM
What is an example of central fatigue?
When a task can not be continued but the muscles can produce the required force when directly stimulated electrically
What is a list of factors that are involved in muscle fatigue?
Potassium ion Decreased ATP Inorganic Pi Lactate and H+ (mostly H+) Muscle pH Muscle Glycogen Depletion Reactive oxygen species
What is the fatigue quotient?
Formula that takes into account the influence of the 3 biomechanical systems that are the basis of muscle function
How is the value of a fatigue quotient evaluated?
The lower the ratio the more fatigue resistant a muscle is
