1. Muscle Physiology KINE 4396/5390 Strength and Conditioning Christopher Ray, PhD, ATC, CSCS Muscle Physiology KINE 4396/5390 Strength and Conditioning Christopher Ray, PhD, ATC, CSCS

2. Objectives  Anatomy of Skeletal Muscle  Muscular contraction  Muscle Fiber Types/Recruitment  Muscle action  Force production

13. Three Types of Connective Tissue: Epimysium, Perimysium, and Endomysium

14. Three Arrangements of Muscle Fibers Fibers parallel to tendon Unipennate muscle Bipennate muscle

15. Fiber Pennation In a pennated muscle not all of the force generated in the muscle fiber is delivered to the tendon. Pennated muscles usually compensate for this disadvantage by increasing the cross-sectional area. Pennated muscles do not move a joint through as large of ROM as do unipennate muscles.

18. A Motor Unit All muscle fibers of a motor unit contract together Connects via a neuromuscular junction –Each cell has 1 –Motor Neuron has many

22. Normal striation, Z disks are perpendicular to myofibrillar axis. Streaming and smearing of the Z disks following eccentric exercise. Delayed Onset Muscle Soreness DOMS

25. Detailed View of Myosin and Actin Protein Filaments in Muscle Six actins surround each myosin

26. T he discharge of an action potential from a motor nerve signals the release of calcium from the sarcoplasmic reticulum into the myofibril, causing tension development in muscle. 

35. Contraction of a Myofibril: Stretched Muscle I-bands are Actin in two adjacent sarcomeres A-bands are Myosin During contraction the H-zone and I-bands decrease.

36. Contraction of a Myofibril: Partially Contracted Muscle

37. Contraction of a Myofibril: Completely Contracted Muscle

38. Contraction of a Myofibril: Stretched Muscle Contraction of a Myofibril: Completely Contracted Muscle H-Zone and I-band shrink

39. Sliding Filament Mechanism/Theory Resting Phase –Little Ca ++ is present so few X-Bridges attached. Excitation-Contraction Coupling Phase –Stimulus spreads thru T-Tubule –SR releases Ca ++ –Ca ++ binds with Troponin exposing bind site on Actin –Myosin binds with Tropomyosin Contraction Phase –ATP downgraded to ADP + P –Myosin arm does work on actin Recharge Phase –Pick up new ATP –Myosin head rotates backward Relaxation Phase –Ca ++ is pumped back into SR

40. C alcium and ATP are necessary for myosin cross-bridge cycling with actin filaments. 

41. T ype II, or fast-twitch, muscle fibers are capable of developing higher forces than Type I, or slow-twitch, muscle fibers— especially at higher velocities of muscle action. 

42. T he number of cross-bridges that are attached to actin filaments at any instant in time dictates the force production of a muscle. 

43. Force Production & Factors influencing Force Motor Unit Recruitment Preloading [holding a wt tightens up the muscles elastic structures]. Cross-Sectional Area –Increasing the cross-sectional area increases strength Velocity of Shortening Angle of Pennation Sarcomere and Muscle Length Prestretching (Stretch-Shorten Cycle) –Eccentric contraction followed by an immediate concentric contraction [Plyometrics] Exercise-Induced Muscle Damage (DOMS) Older Muscle –Sarcopenia (reduced muscle size & strength with age) Muscle Fiber Type –Type I (SO) aerobic fiber, low force, slow rise time –Type IIa (INT) anaerobic fiber, high force, shorter rise time –Type IIb (FT) anaerobic fiber, very high force, fastest rise time

44. M any factors may affect rate of cross- bridge cycling and thus force, including neural activation, calcium concentration, myosin ATPase activity, preloading, prestretch, muscle fiber type and ultrastructure, fatigue through a variety of mechanisms, and number of contractile components (myosin and actin) in parallel. 

45. Improving Force Production Use preloading during training to develop strength early in ROM. Accomodating resistance apparatus (hydraulic, isokinetic) do not load the muscle prior to contraction. Increase cross-sectional area of muscle by using moderate resistance (65-80%) for max or near max # of reps. When overloading eccentrically use heavy resistance. When training for explosive concentric use light resistance. Prestretch a muscle before concentric to enhance force production. Incorporate rest days into training cycle to avoid training with DOMS and allow muscle time to repair.

46. Questions In an attempt to increase his 1 rm bench max; George increased his resistance and added negatives. He complains of increased soreness 48 hrs later. What is the soreness called? What is the cause? What is occurring –Resistance is greater than muscle force –Resistance and force is equal –Resistance is less than muscle force

47. Muscles with long fiber lengths generate greater velocity and move segment thru greater distance. Short length with high cross-sectional area yields high force.

48. Isometric, Concentric, Eccentric & Stretch-Shorten Contractions Notice that the force goes down in the concentric contraction and up in the eccentric contraction, when compared to the isometric contraction. a) Isometric followed by concentric contraction. The area under c of the Force- Length graph represents the work done in the concentric phase. b) Eccentric followed by concentric contraction (Stretch-Shorten Cycle). During the eccentric contraction energy is stored in the muscle-tendon which results in a more powerful concentric contraction. Compare the area under the c portion of the Force-Length graph. This additional work represents the Force Potentiation due to the SSC. Concentric velocity is the same.

49. Three Types of Connective Tissue: Epimysium, Perimysium, and Endomysium

51. Concentric Actin-Myosin Cycle

52. Eccentric Actin-Myosin Cycle

53. Isometric Actin-Myosin Cycle

54. Relationship Between EMG Signal and Motor Unit Force The EMG signal of a ST motor unit can be described as low amplitude and long duration. The EMG signal of a FT motor unit can be described as high amplitude and short duration. When an ST motor unit fires, it yields a relatively small amount of force with a longer time to peak force, when compared to a FT motor unit. Since FT units are highly fatigable, the CNS is very protective of them. FT units are recruited when a rapid force is needed or only at high force levels.

56. Size Principle (Recruitment Threshold) Small [Slow Twitch, Type I] are recruited first Intermediate [Type IIa] are then recruited Large [Fast Twitch IIb] are recruited last The vertical lines indicate when a motor unit has fired. When the lines are closer together, the motor unit has increased its firing rate. Fast twitch units are the first to be de-recruited, followed by intermediate and finally slow twitch units. Notice that motor units are recruited and de-recruited at about the same force level. ST motor unit FT motor unit

57. Recruit ST Recruit INT Recruit FT Increase firing rate of currently active motor units In a ballistic movement, motor units are recruited simultaneously and they fire at a high or maximal rate at the onset.

58. Force - Length Relationship for Contractile Element At short lengths the filaments overlap and the force declines due to interference. Force is maximized at optimal length because the filaments are able to make more actin - myosin bonds. At long lengths the filaments can not all reach each other and the force declines.

59. Force – Length & Muscle Architecture The Force-Length relationship is affected by the muscle/tendon architecture and the changes in the moment arm.

60. Force-Velocity Curve for Eccentric and Concentric Actions

61. Three Types of Connective Tissue: Epimysium – outer layer Perimysium – surrounds each group of fibers Endomysium – surrounds each fiber All of the connective tissue is continuous with the tendon; meaning Tension developed is transmitted Tendons connect?

62. Sectional View of a Muscle Fiber