Module 5 - Biomechanics of Tissues Flashcards
What contributes to the Force-Length Relationship?
- Active Elements
- Passive Elements
What is the Force-Length relationship as important as?
- Effects of leverage
What is the Force-Length Relationship also known as?
- Length-Tension Relationship
What are the Active parts of the Force-length relationship?
- Thick Filament: Myosin
- Thin Filament: Actin
What happens in an Ascending Limb?
- Muscle force increases
- 2 Subregions
What are the two subregions of the active part of the ascending limb?
- Steep
- Shallow
What is the steep subregion of the active part of an ascending limb?
- Associated with force required to deform thick filament
- F = 0 at 1.27um
What is the shallow subregion of the active part of an ascending limb?
- Overlap of thin myofilaments
- Actin filaments from one side overlap with those on the other side
- Interferes with the formation of cross-bridges
What happens in a plateau region of the active part of the Force-Length?
- Muscle Force remains constant
What does the plateau region correspond to?
- central region of myosin fiber that does not have cross-bridge (0.2um)
- If Greater Fiber overlap, no additional cross-bridge formation
What happens in the descending limb active part of the force-length relationship?
Muscle force decreases
- sarcomere length increases
- overlap between myosin and actin decrease
- decrease in the number of available cross-bridges
- Muscle force decreases until no overlap
Compare cross-species muscle force activation.
- Length of thick filaments is approximately the same (1.6um)
- Plateau and descending limb are identical (shifted)
- Length of thin filament changes between species
- Longer for humans: estimated 1.27um
- The main difference occurs in ascending limb of force-length relationship
What is the main difference of force-length relationship between species?
- Thin filament
- Ascending limb
What are the effects of muscle fiber length (with identical physiological cross-sectional area)?
- Increased muscle active range
- Identical Maximal Tension, but occurs at longer muscle length
What are the effects of Muscle cross-sectional area (with identical muscle fiber length)?
- Increased maximal tension
- Muscle active range remains the same
Explain the passive part of the muscle force-length relationship.
Including the Muscle (not the tendon)
- Titin molecule spans half the sarcomere
- Titin corresponds to the passive mechanical properties of muscle
What are the sources of passive tension in muscles?
Parallel
- Fascia Layers of Muscle
Series
- Possible role of Titin
What is Titin?
- Giant Protein: 10 times heavier than average protein
Where is the Titin Molecule located?
Spans half the Sarcomere
- Z-band to M-line
What does the Titin Molecule do?
- Stabilizes myosin in the middle of the sarcomere
- Influences the force-length relationship, both active and passive part
What is the differences in Cardiac Muscle and the Soleus Muscle in relation to the Titin Molecule?
- Cardiac Muscle is 10x stiffer than soleus muscle
- Corresponds to changes in Titin molecule (number of amino acids)
What are some examples of lower leg muscles with variations in the force-length relationship?
Semitendinosus
- Descending Limb
Rectus Femoris
- Ascending & Descending Limb
Gastrocnemius
- Ascending Limb
What also must be applied to a patients muscle-joint system along with force-length relationship?
- Geometry of the joint is also important to understand joint function/dysfunction
Is the Rectus Femoris a Biarticular Muscle?
Yes
- Hip Flexor
- Knee Extensor
What is the range of knee motion in running and cycling?
- full extension 120 degrees
What is the range of hip flexion in running and cycling?
- Trunk-thigh angle of 25-30 degrees is expected in cycling
- much greater angle for running
How does the use of the rectus femoris vary between runners and cyclists?
- Used at different lengths
- Considerably longer for runners
How does the rectus femoris contribute to knee extension in running and cycling?
Runners
- Strong at longer lengths
- Weak at shorter lengths
Cyclists
- Weak at longer lengths
- Strong at shorter lengths
What are some possible explanations for the variation in runners and cycling rectus femoris usage?
Chronic Adaptation to Training
- Change in number of sarcomeres in series within a given muscle fiber of constant length
- Change in number os sarcomeres in series will change the optimal length of the muscle
What happens with changes in the number of sarcomeres in series within a given muscle of constant length?
- Change the optimal length of the muscle
What is different between the active and passive muscle component contribution to force-length relationship?
Both contribute
- Passive only contributes at long sarcomere length
What can training do to the force-length relationship?
- May result in changes
