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How and why do our limbs move? 10/22

How and why do our limbs move? 10/22. How do muscles work through levers to generate force and cause limbs to pass through a range of motion? What does mechanical advantage tell us? What terms are used to describe muscles? What muscles return limbs to their original position?

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How and why do our limbs move? 10/22

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  1. How and why do our limbs move? 10/22 How do muscles work through levers to generate force and cause limbs to pass through a range of motion? What does mechanical advantage tell us? What terms are used to describe muscles? What muscles return limbs to their original position? What types of muscle do we have?

  2. Biomechanics describes what a limb can move and why it can (cannot) move it. • Muscle Contractions: shorten their length to exert force on a tendon (EFFORT) • Resistance: What the muscle attempts to move against (Gravity or elasticity or other LOAD) • Fulcrum: fixed point that motion occurs across • Effort Arm: distance from fulcrum to muscle insertion • Resistance Arm: distance from fulcrum to resistance site

  3. By shortening the length of a muscle, contractions create force. Tendons then transmit force to bones at the insertion. Ligaments limit the range of motion. • What three types of lever do muscles use: • 1) Tilt head back? First ClassTeeter-Tooter • 2) Close Jaw? Second ClassWheelbarrow • 3) Lift Leg? Third ClassTweezers MATH: What is mechanical advantage? MA=Le/Lr MA is a ratio of output force to input force • HighMA= High Power: can move against a large resistance • At cost of low mobility and slow speed (range of motion) • MA greater than 1.0 • LowMA= Low Power: can move limb quickly • At cost of inability to move against a big resistance • MA less than 1.0

  4. How does a first class level prevent your head from drooping during a lecture (nap)? Dr Wilson’s jaw and neck: Effort Arm: 5 cm Resistance Arm: 15 cm MA= 5cm/15cm = 0.33 First Class levels work like teeter tooters!Trapezius(muscle)-Fulcrum-Gravity(Resistance

  5. Second class levers generate force in a manner similar to that of a wheel barrow.Fulcrum---↑Resistance---↑Effort (muscle)

  6. Third-class levels generate force in a manner similar to that of a tweezers.↑Resistance---↑Effort (muscle)---Fulcrum

  7. Ultimately MA describes how easy it will be to accomplish a desired range of motion. • Why do we develop large biceps brachii to move things? • Why do you need large temporalis muscles to crack a nut on your molars (back)? • Why can’t you crack the nut on your incisors (front)? • Why isn’t the digastric muscle larger than the temporalis? • Why do muscles atrophy when in space? • Remember: that with respect to muscle exercise only increase the size of individual myocytes, not the number of myocytes.

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