The Muscular System

1. The Muscular System • Organ Level Structure & Function • System Level Structure & Function • Injury to the Musculoskeletal System • Muscular Analysis

2. System Level Structure and Function • General Structure & Function • Multiarticular Muscles • Muscle Actions • Muscle Coordination

3. System Level Structure and Function • General Structure & Function • Multiarticular Muscles • Muscle Actions • Muscle Coordination

4. Simple Joint System

5. General System Level Function Force & Torque Production (for stabilization and/or movement)

6. Factors that Affect Force Output • Physiological factors • Cross-sectional area • Fiber type • Neurological factors • Muscle fiber activation • Rate of motor unit activation • Biomechanical factors • Muscle architecture • Length-tension relationship • Force-velocity relationship CHRONIC CHRONIC ACUTE CHRONIC? ACUTE CHRONIC? ACUTE CHRONIC? ACUTE CHRONIC? ACUTE CHRONIC?

7. Lengthening-shortening contraction in which the active muscle is stretched before it shortens  Force & work Mechanisms  time to develop force  elastic energy storage in SEC Force potentiation at CB  response of stretch reflex The Stretch-Shortening Cycle

8. Reflex Control – The Reflex Arc

9. Reflex Control – Stretch Reflex

10. Mobility Determined by Torque Output Factors that Affect Torque Output • Force • Moment arm • Point of force application (attachment site) • Angle of force application (muscle insertion angle)

11. Muscle Attachments • Further from joint is better (theoretically) • Structural constraints negate #1 • Cannot alter attachment sites • Strength differences due, in part, to attachment differences

12. Muscle Insertion Angle • 90 is better • MIA typically < 45 • MIA not constant through joint ROM, affecting strength through ROM • Cannot alter MIA • Strength differences due, in part, to MIA differences

13. Understanding Moment Arm Changes Through ROM JA = 90° MIA = 90 ° JA = 45° MIA = 120 ° JA = 30° MIA = 150 ° JA = 150° JA = 120° MIA = 60 ° MIA = 30 °

14. Understanding Moment Arm Changes Through ROM JA = 90° MIA = 90 ° JA = 45° MIA = 120 ° JA = 30° MIA = 150 ° JA = 150° MIA = 30 ° JA = 120° MIA = 60 °

15. Understanding Moment Arm Changes Through ROM JA = 90° MIA = 90 ° JA = 45° MIA = 120 ° JA = 30° MIA = 150 ° JA = 150° MIA = 30 ° JA = 120° MIA = 60 °

16. Biceps Brachii Strength Torque (Nm) 0 90 180 Joint Angle (°) Joint Angle

17. JA = 90° MIA = 90 ° JA = 120° MIA = 60 ° JA = 150° MIA = 30 ° Understanding Rotational Effects Through ROM

18. JA = 30° MIA = 150 ° JA = 45° MIA = 120 ° Understanding Rotational Effects Through ROM

19. JA = 90° MIA = 20° JA = 120° MIA = 20° JA = 150° MIA = 20° JA = 45° MIA = 20° JA = 30° MIA = 20°

20. Brachioradialis Strength Torque (Nm) 0 90 180 Joint Angle (°) Joint Angle

21. Summary of System Level Rotational Function • Torque output varies across ROM • Variation depends on: • Force-length changes • Moment arm changes • Variation differs across muscles & joints

22. Muscle Force for Joint Stability Joint stability for injury prevention determined by linear effects of muscle pull.

23. JA = 120° MIA = 60 ° JA = 90° MIA = 90 ° JA = 150° MIA = 30 ° Understanding Linear Effects Through ROM

24. JA = 30° MIA = 150 ° JA = 45° MIA = 120 ° Understanding Linear Effects Through ROM

25. JA = 90° MIA = 20° JA = 120° MIA = 20° JA = 150° MIA = 20° JA = 45° MIA = 20° JA = 30° MIA = 20°

26. System Level Stabilization Function • Stabilization role varies with • MIA • Bony structure • Other muscle forces • External forces

27. Ftangential Effects of Bony Structure Fnormal Ftangential Fnormal Ftangential Fnormal Source: Mediclip. (1995). Baltimore: Williams & Wilkins.

28. Effects of Other Muscle Force

29. Effects of External Forces

30. Effects of External Forces

32. System Level Function: Key Relationships • What is the relationship between MIA & moment arm (MA)? • What is the relationship between MIA & JA? • What is the relationship between JA & MA? • What is the role of the normal component? • What is the relationship between the normal component and the MIA? • What is the role of the tangential component? • What is the relationship between the tangential component and the MIA?

33. General Structure & Function: Summary • Torque output of muscle is affected by anything that affects moment arm or force output of muscle organ. • Acute changes in torque through ROM dependent on force-length & MIA changes. • Chronic changes in muscle torque dependent on training effects on physiological, neural, and biomechanical factors that affect force.

34. General Structure & Function: Summary • Muscle force for stabilization function determined by physiological, neural, and biomechanical factors that affect force as well as MIA. • Stabilization function defined by presence of • Bony structure • Other muscle forces • External forces

35. System Level Structure and Function • General Structure & Function • Multiarticular Muscles • Muscle Actions • Muscle Coordination

36. Advantages Couples the motion at multiple joints  shortening velocity as compared to one-joint Redistributes power & torque throughout limb Disadvantages Active insufficiency Passive insufficiency Multiarticular Muscles

37. Active insufficiency

38. Active Insufficiency

39. Active Insufficiency

40. Passive Insufficiency

41. System Level Structure and Function • General Structure & Function • Multiarticular Muscles • Muscle Actions • Muscle Coordination

42. Related Terminology • muscle action – the development of tension (force) by a muscle • functional muscle group – a group of muscles that are capable of causing a specific joint action (e.g., wrist radial deviators) • motive force (or torque) – force causing the observed movement • resistive force (or torque) – force opposing the observed movement

43. Types of Muscle Actions • Concentric • Eccentric • Isometric

44. Concentric • Shortens to cause movement • Rotational movement • Mechanically: Net Muscle (Motive) Torque > Net Resistive Torque

45. Eccentric • Lengthens to resist, control, or slow down movement • Rotational movement • Mechanically: Net Muscle (Resistive) Torque < Net Motive Torque

46. Isometric • Stays the same so that bone will stay fixed • No movement • Mechanically: Net Muscle Torque = Other Torque Total Net Torque = 0

47. System Level: Muscle Actions • Resulting motion dependent on all torques acting about the joint (net torque) Conditions for concentric? Eccentric? Isometric?

48. Influence of Gravity & Speed • Downward (with gravity) • Upward (opposing gravity) • Horizontal (perpendicular to gravity) • Consider direction & speed of movement relative to gravity

49. System Level Structure and Function • General Structure & Function • Multiarticular Muscles • Muscle Actions • Muscle Coordination

50. Muscle Coordination: Roles that Muscles Play • Agonists • Antagonists • Stabilizers • Neutralizers