Factors Influencing Production of Muscular Tension and Applied Force n Force-velocity relationship -...
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Transcript of Factors Influencing Production of Muscular Tension and Applied Force n Force-velocity relationship -...
Factors Influencing Production of Muscular Tension and Applied
Force
Force-velocity relationship - Fig 6.17, p 162 Length - tension relationship - Fig 6.18, p 164
- Elastic and contractile components
Biomechanics of musculoskeletal system (pp 420-436) -Objectives
Identify the musculoskeletal machines and machine functions found in the human body
Identify elements of the lever 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 levers and wheel and axle
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)
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 )
Mechanical advantage
Mechanical advantage is the output force (F) divided by input force (R)
Lever arrangements• MA = output force (R) divided by input force (F) = force arm (f)
divided by resistance arm (r)
Wheel and axle arrangements• Very similar to lever arrangements with force applied to the axle,
which is usually the case (e.g., shoulder joint in throwing) with radius of axle and radius of wheel equivalent to force arm (f) and resistance arms (r), respectively
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 Self-study questions
- Introductory problems, p 445 - # 1,2,3,6,7
Assume force is applied perpendicular to the bar:a. In which position will the exercise be easier?b. If it takes 100 N to move the system at position 2, what will it take to lift it at positions 1 and 3?
Hint: use the law of levers: Ff = Rr and solve for F
Homework # 7 – Musculoskeletal machines: (due Monday, 3/15/04)Introductory problems, p 445 - # 4, 8Additional problems, p 446 - #3Exercise equipment problem illustrated below: