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Skeletal Muscle Mechanics

Skeletal Muscle Mechanics. Types of contraction Static Dynamic Experimental models of contraction Muscle mechanics Static Dynamic. Types of contraction. Static contractions: Isometric Dynamic contractions: Concentric (shortening) Eccentric (lengthening).

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Skeletal Muscle Mechanics

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  1. Skeletal Muscle Mechanics • Types of contraction • Static • Dynamic • Experimental models of contraction • Muscle mechanics • Static • Dynamic

  2. Types of contraction Static contractions: Isometric Dynamic contractions: Concentric (shortening) Eccentric (lengthening)

  3. Experimental models of muscle contraction • In vitro: muscle tissue removed from the animal or person (whole muscle, muscle fiber bundle, single fiber) • In situ: muscle remains essentially in place in the animal, but the entire muscle is not intact (e.g., distal tendon is detached and attached to a force transducer) • In vivo: torques are measured across joints in intact humans or animals

  4. Muscle mechanicsStatic contractions Length-tension relationship (Po, Lo) Gordon, Physiology and Biophysics, Saunders, 1982

  5. Muscle mechanicsStatic contractions Length-tension relationship (Po, Lo) Brooks et al.

  6. Muscle mechanicsStatic contractions Twitch (TPT, ½ RT) Slow twitch vs. fast twitch Twitch speed is determined by (a) myosin ATPase activity (myosin HC isoform) and (b) SR concentration Brooks et al.

  7. Muscle mechanicsStatic contractions Twitch, summation, tetanus: Rate coding Brooks et al.

  8. Muscle mechanicsStatic contractions Brooks et al.

  9. Muscle mechanicsDynamic contractions McMahon, Muscles, Reflexes, and Locomotion, Princeton, 1984

  10. Muscle mechanics To review, determinants of force/power production by a muscle 1. # of motor units recruited (i.e., the cross-sectional area of the active muscle) 2. frequency of stimulation (i.e., rate coding) 3. length of the fibers relative to Lo 4. velocity (shortening and lengthening) a. myosin ATPase activity b. SR concentration 5. muscle architecture a. orientation of fibers to the long axis b. the # of sarcomeres in series

  11. Muscle mechanicsStatic contractions Active state muscle model McMahon, Muscles, Reflexes, and Locomotion, Princeton, 1984

  12. Muscle mechanicsStatic contractions Active state muscle model McMahon, Muscles, Reflexes, and Locomotion, Princeton, 1984

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