Lecture 14 - Torque and Mechanical Action of Muscle Flashcards
What are the four parts of a lever system?
Bar, Fulcrum (A), Applied force (F), Resistance force (R).
What are the three classes of levers and their relationships between the fulcrum, applied force, and resistance force?
1st class: R-A-F (e.g., Teeter-totter)
2nd class: F-R-A (e.g., Walnut cracker)
3rd class: R-F-A (e.g., Bicep curl).
What is the mechanical advantage in a lever system?
Mechanical advantage is calculated as the force arm divided by the resistance arm.
Visual representation on heidi’s notes
How does mechanical advantage relate to the class of lever and its effect on force and range of motion?
Less than 1:
- Applied force is greater than resistance force
- Seen in first and third class levers
- Leading to a greater range of motion.
Greater than 1:
- Applied force is less than resistance force
- Seen in first and second class levers
- Requiring less force to move the resistance.
What class of lever is most common in the human body and what are its benefits?
Most levers in the human body are 3rd class
Promoting speed and range of motion but requiring muscles to exert more force than the load.
How is torque related to human movement?
Human motion depends on the rotation of body segments around joints, caused by torques. Muscles create torque at each joint they cross.
Review the Image under “How Does Muscle Create Torque?” IN NOTES
What components are involved in the muscle angle of attachment and their effects?
Rotary component: Perpendicular to the bone, applied force.
Stabilizing/dislocating component: Along the axis on the bone, either pulling into or away from the joint. Not part of the classic lever system
The torque created by a muscle around a joint can be calculated in two ways:
Tmuscle = Fm x moment arm
Tmuscle = Fm rotary x L (distance of attachment)
In both cases, Tmuscle = Fm x L x Sin
How does muscle force cause rotation in the context of the knee and lower leg?
Muscle force pulls off-axis, creating a torque with the knee joint acting as the fulcrum. The quadriceps muscle develops rotary force, which is primarily stabilizing with little contribution to rotation.
What is net joint torque and its significance?
Net joint torque is the vector sum of all individual torques exerted by muscles at a joint, determining the direction of agonist action at any given time.
How can you determine if a muscle is acting concentrically or eccentrically during movement?
Combine muscle torque data with joint velocity data. If both are moving in the same direction, it’s concentric.
If muscle torque is active but joint movement is in the opposite direction, it’s eccentric.
REVIEW the “Resultant Torque; Muscle Activity” section in notes to understand GRAPHS
