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“Torques/ moments” Levers Systems.

“Torques/ moments” Levers Systems. 9 th Lecture. Dr .Manal Radwan Salim Lecturer of Physical Therapy Pharos University 21/12/2013. Torque (moment): Torque can be considered as a rotatory equivalent of force. A torque rotates an object about an axis of rotation.

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“Torques/ moments” Levers Systems.

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  1. “Torques/ moments” Levers Systems. 9th Lecture Dr .Manal Radwan Salim Lecturer of Physical Therapy Pharos University 21/12/2013

  2. Torque (moment): Torque can be considered as a rotatory equivalent of force. A torque rotates an object about an axis of rotation. Torque (moment) Equals: The product of a force multiplied by its moment arm. Moment = force * moment arm. Units:Newton. meter (n.m).

  3. The external torque has the potential to rotate the forearm in a clockwise, or extension direction. When the sum of the counterclockwise torques equals the sum of the clockwise torques, no turning will occur.

  4. *Torque can be classified according to their effect: • probelling torque. • Resistive torque. • **Torque can be classified according to their Source into: • Internal torque: product of internal force and its internal moment arm. • Internal moment arm: distance between the axis of rotation and the perpendicular intersection with a muscle (internal force).

  5. b) The external torque is defined as the product of the external force (gravity) and the external moment arm. The external moment arm is the distance between the axis of rotation and the perpendicular intersection with the external force. The external torque has the potential to rotate the forearm in a clockwise, or extension direction.

  6. Mechanical advantage of torques: is the ratio of the internal moment arm to the external moment arm. n.b. in the human body, the mass or weight of a segment that is due to gravitational force can be changed only by changing the length of the moment arm in relation to the axis. This is done by moving a body segment.

  7. Methods of torque estimations: A- In Single force: moment= force * perpendicular distance (line) between point of application of force to axis of rotation. If perpendicular distance not known: so we make resolution of the force into two components which act at the right angle to each other. The component which acts along the radius has a zero torque since its line of action passes directly via point of rotation. We will deal with torque product by the component acting at right angle too the radius.

  8. Task 2Why Change in elbow joint angle affect both internal and external torque potential

  9. Levers Definition: lever is a simple machine, which consists of a rigid bar that can move or rotate around a fixed point or a fulcrum when a force is applied to overcome resistance. *The force is called the effort. *Effort arm:the perpendicular distance from the line of action of force to the fulcrum is called ( the effort arm ) *The resistance is called the load. *resistance arm:the perpendicular distance from the line of action of resistance and the fulcrum is ( the resistance arm )

  10. Human Equivalent of levers Human body is a complex system of levers 1-Bone is the rigid bar. 2-Joint axis is the fulcrum. 3-Muscles produce the effort. 4- Resistance is represented by the weight of the segment/ extremity plus any weights attached to the segment. 5- The effort arm is the moment arm of the muscular force. 6- The resistance arm is the moment arm of the gravitational line of action.

  11. *The mechanical advantage value of lever determines its function. • Levers serve two important functions 1- overcome resistance larger than the magnitude of the effort applied 2- increase the speed or range of motion through which a resistance can be moved.

  12. Mechanical advantage (MA) of the lever *MA= Effort arm/ Resistance arm.

  13. Classification of lever: Levers are classified according to the manner of arrangement of the applied force /effort (E), the Falcrum /axis (F), and the resistance /load (L) in relation to each other into:

  14. 1- First class lever: See saw About 25% of the muscles in your body operate as first class levers

  15. Anatomical Examples for 1st Class Levers: • In The Axial Skeleton Position: • Action of neck extensors against weight of head. • Fulcrum (Axis): • Atlanto-occiptal joint. • Resistance: • The weight of head. • Effort (Force): • Made by the neck extensors.

  16. b) In The Lower Limb: Non-weight bearing planter flexion. Effort (Force): Planter flexors ( gastrocnemuis and soleus ). Fulcrum (Axis): Ankle joint. Resistance: Segmental COG of foot.

  17. 2- Second Class Lever: Wheel barrow Nut cracker

  18. Anatomical Examples for 2nd Class Levers: Very few examples of 2nd class lever in human body. Because the humans are not designed to apply great forces via lever systems a) The Axial Skeleton Masseter muscle during eating - chewing Resistance: Food Fulcrum (Axis): Tempromandibular joint - TMJ Effort (Force): Insertion of masseter muscle at the lower border of mandible

  19. b) In the Lower Limb Calf muscles in weight bearing planter flexion (raising body on toes). Fulcrum (Axis): Base of toes. Resistance: Body weight LOG anterior to ankle joint. Effort (Force): Contraction of calf muscles.

  20. 3- Third Class Lever: Stapler

  21. c) In the Upper Limb: Fulcrum (Axis): Resistance: Effort (Force):

  22. Anatomical Examples for 3rd Class Levers: 3rd class is the most common example inside body because humans are built for speed more than strength. Example In the lower limb: Quadriceps muscle during knee extension Fulcrum Knee joint Resistance weight of leg and foot segmental COG Effort Tibial tuberosity (insertion of quardriceps muscle).

  23. Two joint muscles: biarticualr muscle. Example: Rectus femoris muscle. Characteristics of Two Joint Muscles: 1- More efficient than the one joint muscle in performing patterns of movements. 2- Active Insufficiency: The muscle cant produce its complete tension at both joints at the same time. In straight leg raising the rectus femoris muscle will lose its tension and the leg will descend downward involuntarily. it must lose some tension over one joint to complete the active range of motion over the other joint.

  24. Characteristics of Two Joint Muscles Cont.: 3- Passive Insufficiency: When the two joint muscle is lengthened over the two joints at the same time, it will cause pain after certain limit. For example, if a subject is trying to touch his toes from sitting or standing ( flexion of the hip joint with extension of the knee joint is done passively by the weight of the upper body), after certain time pain will be felt at the posterior part of the thigh which is the location of the hamstring muscles.

  25. Rectus Femoris Muscle: two joints move in opposite direction

  26. Hamstrings Muscle: two joints move in opposite direction

  27. Finger Flexors Muscles: two joints move in same direction Flexor digitorum superficialis Flexor digitorum profundus

  28. Finger Flexors Muscles: two joints move in same direction

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