Lecture Notes: Axial Skeleton, Muscle, and Joint Interaction

Introduction

• Presenter: Dr. Alexandra Kopelevich
• Topic: Interaction between axial skeleton, muscles, and joints
• Main Functions of Axial Muscles:
  • Control posture during movement
  • Stabilize axial skeleton during upper or lower extremity movement
  • Protect vital organs and neural structures
  • Generate intrathoracic and intra-abdominal pressure
  • Produce torque for movement

Torque Production

• Torque Potential Equation:
  • Product of muscle force (parallel to given plane) x length of internal moment arm

Flexion and Extension

• Axis of Rotation: Right medial to lateral through the intervertebral body
• Muscles Involved: Longissimus, Rectus Abdominis
• Key Points:
  • Rectus abdominis has a longer lever arm, allowing easier torque generation
  • Longissimus requires more force to produce torque

Lateral Flexion (Frontal Plane)

• Muscles Involved: Obliquus externus abdominis, Iliocostalis
• Key Points:
  • Lateral positioning to axis allows generation of lateral flexion torque
  • Iliocostalis requires more force due to shorter lever arm

Rotation (Horizontal Plane)

• Muscles Involved: Multifidus, External Obliques
• Key Points:
  • External oblique sits farther from axis, allows more torque generation

Lifting and Lumbar Load

• Biomechanics Examined in Lifting:
  • Muscle peak force, ligamentous tension, compression, and shear forces
• Safety Guidelines:
  • NIOSH recommends maximum lumbar load of 3,400 newtons (764 pounds)

Force Calculation Example

• Scenario: Lifting object in sagittal plane
• Forces Considered:
  • Muscular force, body weight, external load
• Torque Calculation:
  • Torque = force x lever arm

Techniques to Reduce Lifting Injury

1. Reduce Lifting Velocity:
   • Decreases extensor muscle force
2. Reduce External Load Weight:
   • Sometimes impractical in certain scenarios
3. Reduce External Moment Arm Length:
   • Lift load between knees to minimize distance
4. Increase Internal Moment Arm:
   • Allows generation of torque with less muscular force

Valsalva Maneuver

• Definition:
  • Increase intra-abdominal pressure by contracting abdominal muscles against closed glottis
• Benefits:
  • Unloads lumbar intervertebral disc junction, increases stiffness and stability

Role of Transversus Abdominis

• Fiber Orientation: Horizontal
• Function:
  • Increases abdominal pressure without flexion torque
  • Stabilizes core without activating extensors

Diaphragm and Lifting

• Function:
  • Inhalation pulls dome inferior, increases intra-abdominal pressure
• Engagement Issues:
  • People with low back pain may not engage diaphragm adequately

Posterior Ligamentous System

• Components:
  • Posterior longitudinal ligaments, ligamentum flavum, Z-joint capsule, interspinous ligaments, thoracolumbar fascia
• Function:
  • Stores force temporarily, helps balance extensor muscular force

Thoracolumbar Fascia

• Structure:
  • Most developed in lumbar region
• Function:
  • Generates passive tension to produce extension torque
• Mechanisms:
  • Flexion of lumbar spine or contraction of muscles like transversus abdominis, internal obliques, and latissimus dorsi

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These notes summarize the key points and concepts covered in the lecture by Dr. Alexandra Kopelevich on axial skeleton, muscle, and joint interaction.