Lecture 17 – Muscle Physiology V

Vary types of motor units and number of units

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Vary types of motor units and number of units Recruitment is adding more motor units by adding more units Stimulated to fire  Recruitment is in a specific order 1. Fatigue resistant slow twitch fibers weak stimulus will cause them to fire lowest threshold
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2. Fatigue resistant, fast twitch oxidative-glycolytic fibers as time progresses you wont see much of a drop off because all units are still fairly  fatigue resistant 3. Glycolytic fast twitch fibers near maximal how do we decrease drop-off from fatigue? Asynchronous recruitment Alteration of active motor units Prevents fatigue only in submaximal contraction Maximal contraction When all are in fused tetanus, they do cycles of partial relaxation You can maintain contraction for a huge amount of time Arrangements of lever Systems Fulcrum between the effort and the load In the head and neck Load between fulcrum and effort Overcomes resistance Achilles tendon Effort lies between fulcrum and load Biceps  Fulcrum is at the elbow joint Load is the center of gravity of your arm
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At static equilibrium F1D1 = F2D2 The distance is always the distance from the fulcrum to either the load or the applied  force F1 is the force of the load and F2 is the force of the muscle This applies no matter what kind of lever system you are using If you are holding a weight it becomes a similar type of equation However, it is SEPARATE – you need to calculate separately how much it takes to lift  your arm if you weren’t holding a weight EG 10 kg weight Joint is the fulcrum, so load is 10 kg and whatever the distance the load is from the arm  (F1D1) F2D2 is the distance from the fulcrum to the effort and F is what you are trying to figure  out The force the muscle needs to exert to lift the load and balance it The biceps system is working at a mechanical disadvantage because the amount of  force that is required to lift an object is generally greater than the force that the object  alone exerts Why the disadvantage?
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