Module 11 - Introducing the Tendon Flashcards
Describe the structure of a tendon
- Not Rigid
- Attach muscle to bone
Why do tendons affect muscle function in a positive way?
- Right amount of compliance
How do tendons form?
- Connective tissue around muscles converge to form the tendon
What do tendons look like?
- White
- Glossy
- Smooth
Describe the difference in tendons regarding the structure
- enclosed in a connective tissue sheath
- some, slide with respect to adjacent tissues and skin
What is the difference in tendons regarding attachment structure?
- some, wrap around pulley
- some, pull in direct line from muscle to bone
What are tendons mainly composed of?
- Collagen
How are the collagen fibers in a tendon arranged?
- Mainly in a staggered pattern
- Create collagen fibril
How do Fibrils relate to tendon?
- Fibrils bundled into fascicles
- Fascicles bundled into tendons
What is a dominant feature of the collagen fibers under a light microscope?
- Wavy appearance
What happens when a tendon is placed under a load?
- Wavy appearance disappears
What is part of tendon compliance?
- Wavy appearance of the collagen fiber
What is the term for the wavy pattern of the collagen?
- Crimp pattern
What other structures contribute to tendon viscoelasticity?
- Glycosaminoglycan
- Elastin
What is stress?
- Resistance developed by tissue when externally loaded
What is strain?
- Deformation of tissue submitted to external load
Do tendons produce active tension?
- No
How is the stress-strain property of tendons documented?
- Tendon connected to a force transducer and stretched
Describe the stress-strain relationship of a tendon at a low load
- Relatively compliant
- Toe Region
What happens to the stress-strain relationship of a tendon as load increases?
- Stiffness of tendon increases
Is the stress-strain relationship of a tendon linear?
- No
What is Young’s Modulus useful for?
- Comparing stress-strain properties of tissues
Why does a tendon strain when going through muscle contraction?
- Muscle applies a load to tendon
What determines the elongation of teh tendon?
- Stiffness of the tendon
What, regarding the tendon, must be well adjusted to positively affect muscle function?
- Load deformation
What is the ratio of Young’s Modulus of the tendon to the passive muscle?
- 100:1
What percentage of strain is the tendon at during maximal isometric muscle tension?
- 3%
Fill in the blank: Tendons are relatively _______ & _____ vascular supply
Acellular & Poor
What does active muscle force generation depend on?
Mainly
- Force-length relationship
- Force-Velocity Relationship
What happens to the tendon when active force develops? What does this mean?
Happens
- Tendon Strains
Means
- Muscle shortens further
What does the magnitude of tendon elongation depend on?
- stress-strain properties
What is the consequence of the tendon regarding isometric contractions?
- Muscle activation at fixed joint angle is not true isometric action
What is the difference between long and short tendons?
- Long tendon deform more when same load is applied
What do you need to do to compare b/w tissues?
- normalize elongation (I - I0 / I0)
How is the control of balance predicted to occur?
- Reflexive control
How do reflexes play into control of balance?
- Generate forces to maintain equalibrium in reaction to movement of body
What happens to the calf muscle during swaying forward?
- Stretched while active: eccentric action
What does the stretched calf muscle do during swaying forward motion?
- Elicite reflexes that leads to increased muscle activity
- Restoration of body position toward a ‘neutral’ position
What did the Loram paper identify about the SOL and Gas muscles during standing balance?
- Paradoxical contraction
- Concentric action on sway forward
- Passive lengthen on sway backwards
What did the Loram paper identify about the tendon?
- Stiffness insufficient for static stabilization
- Contrasts spring-like stiffness regulation of balance
What did the Loram paper identify about control of balance?
- controlled through repeated impulses
- Transient shift in muscle length
What should we consider about velocity when a joint is allowed to move?
Even if muscle-tendon unit shortens at constant velo
- fiber and tendon may not shorten at constant velo
When are the simple biomechanical models to estimate muscle fiber length/velocity during various muscle actions useful?
- to estimate muscle-tendon unit length
What is needed to measure muscle fiber length/velocity?
- direct measure
Does the development of active muscle tension occur instantly following the activation of the muscle?
- No
What is the delay between active muscle tension and the activation of the muscle called?
- Electro-mechanical delay
What is the elctro-mechanical delay subdivided into?
- Excitation dynamics
- Contraction dynamics
What is excitation dynamics?
- Delay associated with muscle stimulation
Where does the excitation dynamics occur?
- Conduction delay in T-tubules
- Release of Ca2+
- Cross-bridge formation
What is contraction dynamics?
- Delay associated with the actual build-up of muscle tension
What will the stretching SEC by contractile elements be affected by?
- Type of muscle action and contraction history
What is the tension development in the contractile element ?
- Type of motor unit recruited (FF: 20ms; S: 100ms)
What is the electro-mechanical delay determined by?
- type of muscle action
How might the emg signal differ from the force signal?
- EMG before Force
What does the delay between emg and force signals depend on?
- Type of muscle action
What avoids the dissociation between msucle activity and force?
- Maintaining isometric action
What leads to a temporal dissociation between muscle activity and force?
- electromechanical delay
- emg and force signal delay
What does the timing of the force delay affect?
- Movement coordination
What does the force-time relationship say about EMG and muscle force?
- EMG not good indicator of muscle force
What amplifies the force-time delay?
- faster movements
- rapid changes in force
When is the electromechanical delay a problem during constant force being applied at static joint angles?
- Onset action
- Offset Action
How is muscle force expressed through the musculoskeletal system?
- As a joint moment
- Causes angular acceleration
What will be detected before velocity and displacement?
- Acceleration
What does tendon compliance do to the force-length relationship?
- Systematic change
What happens when the tendon is perfectly stiff?
- Acts as a rigid linkage between muscle and bone
What does a perfectly stiff tendon do to the force-length relationship?
- offsets it
What does tendon compliance result in regarding the force-length relationship?
- rightward shift
Why does tendon compliance result in a rightward shift of the force-length relationship?
- Added elasticity in series
- Sarcomeres can shorten at expense of tendon elongation
What does a longer tendon in series result in regarding the force-length relationship?
- Greater rightward shift
What causes a differential degree of sarcomere shortening?
- Initial length of tendon
What is the tendon strain at max isometric contraction?
- 3%
What increases the range over which the muscle-tendon unit curve operates? by how much?
Tendon compliance
- 50%
What causes a shift of the muscle’s optimal length?
- Shift in optimal sarcomere length
- Tendon compliance
What do modest changes at the sarcomere force-length relationship lead to?
- changes at whole muscle level
What whole muscle level changes does the sarcomere force-length relationship change that occurs due to tendon compliance cause?
- Operating range increase: 50%
- Shift in optimal length
What is an increase in operating range and shift in the optimal length of a whole muscle a result of?
- sarcomere shortening at expense of tendon lengthening
What would happen if the tendon was too stiff?
- No benefit to muscle
What happens if the tendon is too compliant?
- Muscle would shorten to nothing
What is an important design parameter of muscle-tendon unit?
- Muscle fiber length ratio
What does the length of the tendon determine?
- The influence of the tendon (operating range & shift in P0)
What is the limit to the benefit of increasing tendon length?
- sarcomere shortens to length with no active force production
What do the flexor digitorum profundus and superficialis have in common?
- long tendons
- located in forearm
What does a long tendon suggest?
- compliant tendon
Why might the Flexor digitorum profundus and superficialis muscle receptors not be able to properly code for the joint position?
Tendon acts like spring
- Lower inertia on fingers
What is the tendon strain at P0 of the Flexor digitorum profundus and superficials? What is this an example of?
- 1.2%
- Specialization of tendon
What is a common pattern of muscle activation?
- Lengthening-shortening muscle action
Describe the lengthening-shortening muscle action
- counter-movement away from the intended direction
- motion slowed by eccentric muscle-tendon unit action
- Followed by concentric action in intended direction
What is an example of a lengthening-shortening muscle action?
- Knee extensor muscle during kicking
- hip,knee, and ankle extension during counter-movement jump
What is the lengthening-shortening muscle action known as?
- Stretch-shortening cycle
What can a muscle do when it is actively stretched before it is allowed to shorten?
- Perform more positive work
What are the performance benefits of stretch-shortening cycle?
10-20%
What mechanisms have been proposed to explain the greater positive work a muscle can do with a stretch-shortening cycle?
- Increases time to full muscle activation
- Stores elastic energy
- Force enhancement: role of titin
- Stretch reflexes: evoked by muscle lengthening
When is the elastic energy storage during a stretch-shortening cycle best able to explain the increase in positive work?
- During Rapid Stretch-Shortening
What best explains the increase in height of a slow countermovement jump (stretch-shortening cycle)?
- Extra time of muscle to develop tension
Where is the elastic energy stored during the lengthening action of the stretch-shortening cycle?
- Elastic components
How does the elastic energy storage of the stretch-shortening cycle influence metabolic cost?
Reduces it
- Elastic energy stored in connective tissues
Describe the energy storage and usage of the Triceps Surae during slow running
Stance Phase
- 45J absorbed
Second phase
- 60J used
What are the advantages of the stretch-shortening cycle?
- Increase in positive work: power production
- Lower metabolic cost
For the same force output, what consumes more energy: Isometric or Eccentric? (how is the tendon involved)
- Isometric: tendon can store energy and restore it
