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Biomechanics of musculoskeletal system (pp 420-436) -Objectives n Identify the musculoskeletal machines and machine functions found in the human body n.

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Presentation on theme: "Biomechanics of musculoskeletal system (pp 420-436) -Objectives n Identify the musculoskeletal machines and machine functions found in the human body n."— Presentation transcript:

1 Biomechanics of musculoskeletal system (pp ) -Objectives n Identify the musculoskeletal machines and machine functions found in the human body n Define torque, quantify resultant torques, and identify the factors that affect resultant joint torques n Describe the concept of net torques and it’s use in estimating muscle force n Describe the elements of the wheel and axle and give examples in the musculoskeletal system of humans n Describe the concept of mechanical advantage associated with the different classes of levers and wheel and axle

2 Musculoskeletal machine functions and machines n Most important machine functions found in the human body -provide advantage for ROM and speed (levers and wheel & axle) -change direction of applied force (pulley) n Three machines found in the body: -levers (ex. biceps brachii pulling on radius) -wheel and axle (rotator cuff muscles pulling on humerus) -pulley (patella, lateral malleolus of fibula)

3 Levers in the Human Body (all amplify movement at expense of force) Class III: Class :I

4 Wheel & Axle: Another movement amplifier!

5 Simple pulley: Changes direction of force application

6 Musculoskeletal Levers n Elements of levers - axis (joint center) -rigid bar (long bone) -motive and resistance torques (muscle pull, gravity, inertia), or moments n Concept of Net Torque n Law of levers (  CW torques =  CCW torques) -Force X Force Arm = Resistance X Resistance Arm - or Ff = Rr n Analysis of musculoskeletal lever system -Turning, or rotary component (Fd sin  ) -Stabilizing and dislocating component (Fd cos  )

7 Concept of Net Torque, concentric and eccentric contraction

8 Muscle force acting on lever systems

9 Sample Problem #2, p 433

10 Analysis of elbow flexors: Note how angle of pull changes

11 Classes of levers & mechanical advantage n Classes of levers -Class I: Axis between force and resistance application (ex. triceps tendon in elbow extension) -Class II: Resistance application between axis & force application (ex: wheelbarrow, obliques and spinal rotation) -Class III: Force application between axis & resistance application (ex: biceps tendon in elbow flexion) n Calculating mechanical advantage -MA = force out (resistance)/ force in (motive force) -MA = motive force arm/resistance force arm

12 Levers in the Human Body (all amplify movement at expense of force) Class III: Class :I

13 Class I Class II Class III

14 Mechanical Advantage: MA = f/r = R/F This lever is a movement amplifier (MA less than 1) If f = 1 cm and r = 20 cm, what would R, the resistance be? F = f =  d = d sin 

15 Wheel and axle and mechanical advantage n Wheel and axle arrangements n Very similar to lever arrangements with radius of axle and radius of wheel equivalent to force and resistance arms -Mechanical advantage Force applied to wheel (ex: obliques in spinal rotation) –MA = radius of wheel/radius of axle Force applied to axle (ex: rotator cuff muscles in humeral rotation) –MA = radius of axle/radius of wheel

16 Wheel and Axle Force applied to wheel: Force applied to axle: Mechanical Advantage is f/r, force arm ÷ resistance arm MA greater than 1 (force amp) MA less than 1 (movement amp)

17 Musculoskeletal pulleys, study questions n Pulleylike arrangements Only simple pulleys found in the body to change direction of force application n General considerations of musculoskeletal machines human body is built for speed & ROM - not force n Study questions -Introductory problems, p # 1,2,3,4,6,7,8 -Additional problems, p #3, 8

18 Ex equipment problem – Assume force is applied perpendicular to the bar: a. What class lever is this? b. In which position will the exercise be easier? c. If it takes 100 N to move the system at position 2, what will it take to lift it at positions 1 and 3?


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