Muscle Mechanics Related to Chapter 11 in the

Muscle Mechanics Related to Chapter 11 in the text http: //highered. mcgraw-hill. com/sites/0072495855/student_view 0/chapter 10/ 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 1

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 Mac. Kenzie - HK 376 11/2/2020 2

Muscle Schematic Illustration muscle fascia fascicle epimysium muscle fibre (cell) perimysium myofibril sacrolemma 11/2/2020 endomysium Dr. Sasho Mac. Kenzie - HK 376 3

Myofibril I - Band A - Band Z Line M Line 11/2/2020 Huxley and Huxley, 1954 Dr. Sasho Mac. Kenzie - HK 376 4

Myofibril sarcomere A-band I-band filament 11/2/2020 Z-line Dr. Sasho Mac. Kenzie - HK 376 5

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 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 6

Cross bridge theory thick filament thin filament Z-line I-Band 11/2/2020 Z-line A-Band Dr. Sasho Mac. Kenzie - HK 376 7

thick myofilament thin myofilament 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 8

Huxley and Huxley, 1954 I - Band A - Band Z Line M Line Sliding filament model Z A I M 1 m thick filaments thin filaments 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 9

Cross bridges globular head tail portion myosin molecule thick myofilament 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 10

Cross bridges 60 o 14. 3 nm 43 nm 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 11

Cross bridge theory rest cross-bridge thin filament thick filament contraction 11/2/2020 sliding Dr. Sasho Mac. Kenzie - HK 376 12

Muscle Force Depends on Four Factors • • 11/2/2020 Sarcomere (muscle) length Velocity of muscle contraction Activation level Previous contraction history Dr. Sasho Mac. Kenzie - HK 376 13

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 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 14

Force-Length Relationship Force [%] plateau region 100 75 50 ascending limb descending limb 25 0 Sarcomere length 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 15

Force-Length Relationship Sarcomere = 1 z-line + 2 thin filament + 1 thick filament - overlaps 0. 10 m 11/2/2020 0. 95 m 1. 60 Dr. m Sasho Mac. Kenzie - HK 376 16

Force-Length Relationship 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 17

Force-Length Relationship b c 11/2/2020 100 tension generated a a b 75 50 25 0 c 1. 5 2. 0 2. 5 3. 0 sarcomere length [ m] 3. 5 Dr. Sasho Mac. Kenzie - HK 376 18

Force-Length Relationship Force [%] plateau 100 2 3 4 75 50 ascending limb 25 0 11/2/2020 5 1 0 1. 27 descending limb 2. 17 2. 00 1. 70 3. 60 [%] Sarcomere Length Dr. Sasho Mac. Kenzie - HK 376 19

Force-Length Relationship General: descending limb ascending limb easy to understand 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. 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 20

Application of F-L Relationship Starting position in sprint Knee angle in weight lifting Design of weight lifting equipment Design of bicycles 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 21

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Velocity of Muscle Contraction eccentric – muscle force isometric concentric + velocity of muscle contraction • Why less force for faster concentric contractions? • Why more force for eccentric contractions? 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 23

Force/Power - Velocity Power Force ST = slow twitch FT = fast twitch FT ST ST FT Velocity 11/2/2020 Velocity Dr. Sasho Mac. Kenzie - HK 376 24

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Activation Level • It takes time for muscle to develop tension 1) 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 2) 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). 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 26

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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. 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 28

• 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. – – 11/2/2020 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 Mac. Kenzie - HK 376 29

NEXT CLASS READ CHAPTER 5 AND Construct a flow chart depicting what the torque developed about a joint depends on. 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 30

muscle fascia facicle epimysium perimysium muscle fibre (cell) myrofibril sacrolemma endomysium 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 31

I Band Z Line thick filaments 11/2/2020 A Band M Line titin thin filaments Dr. Sasho Mac. Kenzie - HK 376 32

globular head tail portion myosin molecule thick myofilament centre of filament 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 33

60° cross bridges on thick myofilament 14. 3 nm 42. 9 nm 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 34

actin globule troponin thin myofilament 38. 5 mm tropomyosin 11/2/2020 actin chains Dr. Sasho Mac. Kenzie - HK 376 35

Sliding filament model: Z A Titin I M 1 µm Cross-section area of thick filaments and thick-thin myofilaments overlap 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 36

Force/Power - Velocity Force / Power [normalized] Force Power 1. 0 0. 5 0 11/2/2020 Velocity 0 0. 2 0. 4 0. 6 0. 8 1. 0[normalized Dr. Sasho Mac. Kenzie - HK 376 37 ]

Sarcomere Length • Maximum overlap of myosin and actin allows for a maximum amount of cross-bridge connection and hence force. 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 38

Force-Velocity Relationship First experiments: • Fenn and Marsh, 1935 • Hill, 1938 Found (“stumbled” onto) the Force -velocity relationship while working on heat production of isolated frog skeletal muscle. 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 39

60 o 14. 3 nm model I 43 nm 60 o model II 14. 3 nm 43 nm model II 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 40

Cross bridge theory myosin filament A B 2 B 1 actin filament M M 4 1 A 1 q A 4 Huxley 1969; Huxley and Simmons, 1971 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 41

Cross bridge theory 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 42

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Knee Extension 11/2/2020 Dr. Sasho Mac. Kenzie - HK 376 44

Active and passive structures Force [N] 60 Accumulated Force-Length passive structures 40 Force-Length 20 Length 0 11/2/2020 0. 5 [cm] 1. 0 1. 5 2. 0 2. 5 Dr. Sasho Mac. Kenzie - HK 376 45

no cross bridges can attach Force [%] plateau region 100 3 2 4 1 z-line 2 thin filament 1 thick filament total length 0. 10 m 1. 90 m 1. 60 m 3. 60 m 75 50 ascending limb descending limb 25 1 0 0 11/2/2020 5 Sarcomere length 3. 60 Dr. Sasho Mac. Kenzie - HK 376 46

all cross bridges can attach Force [%] 100 2 3 4 1 z-line 2 length thin filament 1 thick filament no overlap total length sarcomer 0. 10 m 1. 90 m 0. 17 m 2. 17 m 75 50 ascending limb descending limb 25 1 0 0 11/2/2020 5 2. 17 Sarcomere length 3. 60 Dr. Sasho Mac. Kenzie - HK 376 47

all cross bridges can attach 1 z-line 2 thin filament 1 thick filament no overlap total length sarcomer Force [%] 100 2 3 0. 10 m 1. 90 m 0. 00 m 2. 00 m 4 75 50 ascending limb descending limb 25 1 0 0 11/2/2020 5 2. 17 3. 60 2. 00 Sarcomere length Dr. Sasho Mac. Kenzie - HK 376 48