Presentation is loading. Please wait.

Presentation is loading. Please wait.

Biomechanics of musculoskeletal system (pp ) -Objectives

Similar presentations

Presentation on theme: "Biomechanics of musculoskeletal system (pp ) -Objectives"— Presentation transcript:

1 Biomechanics of musculoskeletal system (pp 420-436) -Objectives
Identify the musculoskeletal machines and machine functions found in the human body Define torque, quantify resultant torques, and identify the factors that affect resultant joint torques Describe the concept of net torques and it’s use in estimating muscle force Describe the elements of the wheel and axle and give examples in the musculoskeletal system of humans Describe the concept of mechanical advantage associated with the different classes of levers and wheel and axle

2 Musculoskeletal machine functions and machines
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) 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
Elements of levers axis (joint center) rigid bar (long bone) motive and resistance torques (muscle pull, gravity, inertia), or moments Concept of Net Torque Law of levers (CW torques = CCW torques) Force X Force Arm = Resistance X Resistance Arm or Ff = Rr 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
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) 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 = d = d sin F =

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

17 Musculoskeletal pulleys, study questions
Pulleylike arrangements Only simple pulleys found in the body to change direction of force application General considerations of musculoskeletal machines human body is built for speed & ROM - not force 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?

Download ppt "Biomechanics of musculoskeletal system (pp ) -Objectives"

Similar presentations

Ads by Google