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Muscle Mechanics

Muscle Mechanics. Related to Chapter 11 in the text. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/. Preparation Hintermann. flexor digiturum longus. flexor halucis longus. tibialis posterior. peroneus brevis. peroneus longus. tibialis anterior.

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Muscle Mechanics

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  1. Muscle Mechanics Related to Chapter 11 in the text http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/ Dr. Sasho MacKenzie - HK 376

  2. Preparation Hintermann flexor digiturum longus flexor halucis longus tibialis posterior peroneus brevis peroneus longus tibialis anterior ext. hallucis longus ext. digitorum longus triceps surea Muscles crossing the ankle joint complex Dr. Sasho MacKenzie - HK 376

  3. Muscle Schematic Illustration muscle fascia fascicle epimysium muscle fibre (cell) perimysium myofibril sacrolemma endomysium Dr. Sasho MacKenzie - HK 376

  4. Myofibril Huxley and Huxley, 1954 I - Band A - Band Z Line M Line Dr. Sasho MacKenzie - HK 376

  5. Myofibril sarcomere I-band A-band filament Z-line Dr. Sasho MacKenzie - HK 376

  6. Cross bridge theory Current paradigm to describe muscle contraction Hugh Huxley and Andrew Huxley published in 1954 two independent papers (which were basically identical) to describe the sliding of the thick and thin filaments past one another.  sliding filament theory Refinished in 1957 by A. Huxley cross bridge theory Dr. Sasho MacKenzie - HK 376

  7. Cross bridge theory thick filament thin filament Z-line Z-line I-Band A-Band Dr. Sasho MacKenzie - HK 376

  8. thickmyofilament thinmyofilament Dr. Sasho MacKenzie - HK 376

  9. Huxley and Huxley, 1954 A - Band I - Band Z Line M Line Sliding filament model M I A Z 1mm thick filaments thin filaments Dr. Sasho MacKenzie - HK 376

  10. Cross bridges globular head tail portion myosin molecule thickmyofilament Dr. Sasho MacKenzie - HK 376

  11. Cross bridges 60o 14.3 nm 43 nm Dr. Sasho MacKenzie - HK 376

  12. Cross bridge theory rest cross-bridge thin filament thick filament contraction sliding Dr. Sasho MacKenzie - HK 376

  13. Muscle Force Depends on Four Factors • Sarcomere (muscle) length • Velocity of muscle contraction • Activation level • Previous contraction history Dr. Sasho MacKenzie - HK 376

  14. Force-Length Relationship Fact: Muscles at very long and very short lengths can not produce high forces Fact: Maximal force production of a muscle depends on its length Dr. Sasho MacKenzie - HK 376

  15. Force-Length Relationship Force[%] plateau region 100 75 50 descending limb ascending limb 25 0 Sarcomere length Dr. Sasho MacKenzie - HK 376

  16. Force-Length Relationship Sarcomere = 1 z-line + 2 thin filament + 1 thick filament - overlaps 0.10 m 0.95 m 1.60 m Dr. Sasho MacKenzie - HK 376

  17. Force-Length Relationship Dr. Sasho MacKenzie - HK 376

  18. Force-Length Relationship a b a 100 75 tension generated 50 b 25 c 0 1.5 2.0 2.5 3.0 3.5 sarcomere length [mm] c Dr. Sasho MacKenzie - HK 376

  19. Force-Length Relationship Force[%] plateau 3 4 100 2 75 descending limb 50 ascending limb 25 5 1 0 [%] 2.17 0 1.27 3.60 2.00 Sarcomere Length 1.70 Dr. Sasho MacKenzie - HK 376

  20. Force-Length Relationship General: descending limb easy to understand ascending limb more difficult to understand Ascending limb: Point 2: Thin filaments overlap partially.A reduced number of cross-bridges can attach. Point 1: Complete overlap of thin filaments.No cross-bridges can attach. Dr. Sasho MacKenzie - HK 376

  21. Application of F-L Relationship  Starting position in sprint  Knee angle in weight lifting  Design of weight lifting equipment Design of bicycles Dr. Sasho MacKenzie - HK 376

  22. Dr. Sasho MacKenzie - HK 376

  23. Velocity of Muscle Contraction isometric concentric eccentric – + muscle force velocity of muscle contraction • Why less force for faster concentric contractions? • Why more force for eccentric contractions? Dr. Sasho MacKenzie - HK 376

  24. Force Power FT ST ST FT Velocity Velocity Force/Power - Velocity ST = slow twitch FT = fast twitch Velocity Dr. Sasho MacKenzie - HK 376

  25. Dr. Sasho MacKenzie - HK 376

  26. Activation Level • It takes time for muscle to develop tension • Electrical signals must be sent from the brain (or spine) to activate muscles. The dynamics of muscle contraction once the signal reaches the muscle also takes time • Even after activation is initiated, there is a delay in the force applied to the bones • At the start of a contraction, the sarcomeres will shorten but will not be able to generate their maximum force. The sarcomeres shorten because the tendons (and other elastic components of muscle) are stretched. The elastic components of muscles and tendons must be sufficiently stretched before the muscular force is transmitted to bone (Springs). Dr. Sasho MacKenzie - HK 376

  27. Dr. Sasho MacKenzie - HK 376

  28. Previous Contraction History • If a muscle is initially contracting isometrically and is then stretched…. ….the muscle will produce a greater isometric force at it’s new length. • Also, a concentric contraction immediately following an eccentric contraction will be more forceful. • This is known as the “force enhancement” phenomenon and has been repeated in hundreds of experiments. • There are several theories behind this behaviour but none are globally excepted. Dr. Sasho MacKenzie - HK 376

  29. In 1994, two men attempted to set a world bungee jumping record by performing the highest double bungee jump in history off of Royal George Bridge. The bridge was located in Colorado and was suspended 300 m above the Arkansas River. John (69.2 kg) and Rory (90.1 kg) used a bungee cord (linear spring) that was 50 m long. John was physically tied to the bungee while Rory simply held onto John. The duo had meticulously planned their jump so that they would come to a stop just as they touched the water. Rory would let go of John allowing him to make his way back to the top and reel John back to safety. • Knowing that the 50 m long bungee cord had a stiffness (k) of 15, was their jump successful? In other words, did the pair come to rest just at the surface of the Arkansas River? (3) • The top of the bungee was fixed to the middle of the underside of a huge metal I-beam. Assuming that 250 KJ of the strain energy was lost as heat (not converted back into kinetic energy) and that the pair dropped in a perfectly vertical path, what happened to John after Rory was dropped into the water? Make sure to include John’s velocity at 300 m above the surface of the river. (3) Dr. Sasho MacKenzie - HK 376

  30. NEXT CLASSREAD CHAPTER 5ANDConstruct a flow chart depicting what the torque developed about a joint depends on. Dr. Sasho MacKenzie - HK 376

  31. muscle fascia facicle muscle fibre (cell) epimysium perimysium myrofibril sacrolemma endomysium Dr. Sasho MacKenzie - HK 376

  32. I Band A Band titin Z Line M Line thick filaments thin filaments Dr. Sasho MacKenzie - HK 376

  33. globular head tail portion myosin molecule thick myofilament centre of filament Dr. Sasho MacKenzie - HK 376

  34. 60° cross bridges on thick myofilament 14.3 nm 42.9 nm Dr. Sasho MacKenzie - HK 376

  35. actin globule troponin thin myofilament 38.5 mm tropomyosin actin chains Dr. Sasho MacKenzie - HK 376

  36. Sliding filament model: Titin Z A M I 1 µm Cross-section area of thick filaments and thick-thin myofilaments overlap Dr. Sasho MacKenzie - HK 376

  37. Force/Power - Velocity Force / Power[normalized] ForcePower 1.0 0.5 Velocity[normalized] 0 0 0.2 0.4 0.6 0.8 1.0 Dr. Sasho MacKenzie - HK 376

  38. Sarcomere Length • Maximum overlap of myosin and actin allows for a maximum amount of cross-bridge connection and hence force. Dr. Sasho MacKenzie - HK 376

  39. Force-Velocity Relationship First experiments: • Fenn and Marsh, 1935 • Hill, 1938Found (“stumbled” onto) the Force-velocity relationship while working on heat production of isolated frog skeletal muscle. Dr. Sasho MacKenzie - HK 376

  40. 60o model I 14.3 nm 43 nm 60o model II 14.3 nm 43 nm model I model II Dr. Sasho MacKenzie - HK 376

  41. Cross bridge theory myosin filament A B2 B1 M4 actin filament M1 A1 A4 q Huxley 1969; Huxley and Simmons, 1971 Dr. Sasho MacKenzie - HK 376

  42. Cross bridge theory Dr. Sasho MacKenzie - HK 376

  43. Dr. Sasho MacKenzie - HK 376

  44. Knee Extension Dr. Sasho MacKenzie - HK 376

  45. Active and passive structures Force [N] Accumulated Force-Length 60 passive structures 40 Force-Length 20 Length 0 0.0 0.5 1.0 1.5 2.0 2.5 [cm] Dr. Sasho MacKenzie - HK 376

  46. no cross bridges can attach 1 z-line 0.10 mm2 thin filament 1.90 mm1 thick filament 1.60 mmtotal length 3.60 mm Force[%] plateau region 3 4 100 2 75 50 descending limb ascending limb 25 1 5 0 0 3.60 Sarcomere length Dr. Sasho MacKenzie - HK 376

  47. all cross bridges can attach 1 z-line 0.10 mm2 length thin filament 1.90 mm1 thick filament no overlap 0.17 mm total length sarcomer 2.17 mm Force[%] 3 4 100 2 75 50 descending limb ascending limb 25 1 5 0 2.17 0 3.60 Sarcomere length Dr. Sasho MacKenzie - HK 376

  48. all cross bridges can attach 1 z-line 0.10 mm2 thin filament 1.90 mm1 thick filament no overlap 0.00 mm total length sarcomer 2.00 mm Force[%] 3 4 100 2 75 50 descending limb ascending limb 25 1 5 0 2.17 0 3.60 2.00 Sarcomere length Dr. Sasho MacKenzie - HK 376

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