Chaper 7 Flashcards
(173 cards)
What does stretching involve?
The Parallel Elastic Component (PEC)
The PEC derives from the muscle membranes and supplies resistance when the muscle is passively stretched.
What specific structures make up the Parallel Elastic Component (PEC)?
- Sarcolemma
- Epimysium
- Perimysium
- Endomysium
These structures are located in parallel with the contractile components.
What primarily contributes to the elasticity of skeletal muscle?
The Series Elastic Component (SEC)
The SEC stores energy when stretched and makes a major contribution to the elasticity of the human skeleton.
What are the major representatives of the Series Elastic Component (SEC)?
- Tendons
- Cross bridges between actin and myosin
Tendons are key in storing elastic energy.
What happens when a tensed muscle is stretched?
The SEC causes a ‘spring-like’ recoil effect
The stretch reflex initiates the development of tension.
What occurs to stored potential energy if the motion is paused?
The energy is dissipated in the form of heat
This results in a lower rebound height.
What are the characteristics of multi-articular muscles?
- Provide advantages
- Display inadequacies
They cannot shorten enough to move all of the joints simultaneously through their full ranges of motion.
Define active insufficiency.
Occurs when the muscle is already shortened by changing the joint angle
This reduces the ability to exert optimal force.
What sensation might one feel during active insufficiency?
A cramping sensation
This occurs because the muscle bunches up.
Define passive insufficiency.
Occurs when the muscle is already stretched and not able to stretch further
This is experienced during deep stretches, such as when reaching to touch toes.
What is the stretch-shortening cycle?
Muscles perform more work when they shorten immediately after being stretched than during isometric contraction
This is important in sports for maximizing performance.
What is the effect of prestretching in the stretch-shortening cycle?
It enhances muscle performance
The concentric phase must follow immediately after the countermovement, without pause.
What is reaction time?
Amount of time required for the motor cortex to address the specific alpha motor neurons
Example: In baseball, the time left for a batter to react is limited.
What is muscle architecture?
The arrangement of muscle fibers relative to the axis of force generation
This is vital in determining contractile properties.
How do sarcomeres arranged in series affect muscle velocity?
They increase the overall velocity of shortening
The velocities become additive.
What is the effect of sarcomeres arranged in parallel?
They increase the capacity for exerting force
More sarcomeres in parallel equate to greater force production.
Define specific force.
The force that can be sustained by the muscle fibers themselves
Specific force values range between 22 to 28 Newtons per sq.cm.
What is physiological cross-sectional area (PCSA)?
It is directly proportional to the maximum tetanic tension of the muscle
PCSA represents the sum of the cross-sectional areas of all muscle fibers within the muscle.
What factors affect the development of tension in muscles?
- Firing frequency
- Muscle fiber recruitment
- Synchronization of active fibers
- Relative size of the muscle
- Temperature of the muscle
- Degree of muscle fatigue
- Degree of pre-stretch
- Angle of muscle pull
Each factor can act independently or together.
What is temporal summation?
The time required for activation, contraction, and relaxation
The mechanical process of muscle contraction lags behind the process of activation.
What is the length-tension relationship?
An optimal length exists for force development, corresponding with maximum overlap of thick and thin filaments
Muscle force is greatest at approximately 120-130% of resting length.
What occurs during eccentric contractions?
The muscle is forced to lengthen due to an external load greater than it can generate
The muscle acts passively, assuming the role of resistance.
What is the force-velocity relationship?
The force generated by a muscle is a function of its velocity
Faster movements result in less ability to exert force.
What is muscle power?
The product of force and velocity
Maximal power output occurs at approximately 30% of maximal contraction force.