Lecture Notes: Biomechanics and Tissue Properties

Announcements

• Lab Schedule:
  • Labs are split this week. Check email for specific times.
  • Make sure to arrive on time due to off-site lab locations.
• Upcoming Schedule:
  • Monday: Elective lecture on spine biomechanics and low back pain.
  • Wednesday: Potential no class if all content is covered.
  • Friday: Last quiz of the semester.
  • Movement Analysis Project Workday in place of Lab 9 due to equipment issues.
  • Monday, May 5th: Exam 3 review.
  • Wednesday, May 7th: Exam 3 study day.
  • Semester ends after presentations.

Lecture Recap

• Previous Topics:
  • Muscle biomechanics: architecture, quality, and factors influencing muscle function.
  • Types of mechanical loads.

Today's Lecture Topics

1. Stress and Strain

   • Stress: Force applied divided by the area of application. Measured in Pascals.
     • Punching with an open hand reduces stress due to larger area.
     • Example: Patellofemoral joint stress during squats.
   • Strain: Measure of deformation in response to stress.
     • Formula: Strain = change in length/original length.
     • Objects with less deformation under stress are stiffer.

2. Tissue Properties

   • Anisotropy: Tissues respond differently depending on the direction of the load.
   • Viscoelasticity: Tissues exhibit different properties based on the rate of loading.
     • Example with water: Slow vs. fast hand entry into water.

3. Bone Biomechanics

   • Protects organs, provides support and attachment sites for muscles.
   • Components:
     • Calcium (stiffness) and Collagen (tensile strength).
     • Bone Cells: Osteoblasts (build), Osteoclasts (remove), Osteocytes (transport metabolites).
   • Remodeling: Constant process influenced by Wolff’s Law.
     • Wolff's Law: Bone adapts based on demand.
     • Strongest in compression.
     • Benefits from rapid high impact loading.

4. Cartilage Biomechanics

   • Articular Cartilage: Thin, covers ends of long bones.
     • Provides stability, distributes forces, reduces friction.
     • Zones:
       • Superficial: Protects against shear.
       • Middle: First defense against compression.
       • Deep: Most resistance to compression.
   • Properties:
     • Anisotropic and viscoelastic.
     • No blood supply; relies on synovial fluid for nutrients.
   • Exercise and Cartilage Health:
     • Exercise crucial for nutrient diffusion.
     • Running supports cartilage health, contrary to common misconceptions.

Stress-Strain Curve

• Elastic Region: Temporary changes; shape returns to normal after stress removal.
• Plastic Region: Permanent changes if stress exceeds elastic limit.
• Ultimate Stress and Failure Point: Where tissue ruptures.

Important Points to Remember

• Understand stress vs. strain and their relation.
• Explain tissue anisotropy and viscoelasticity.
• Define modulus of elasticity and identify tissue stiffness.
• Components of the stress-strain curve.
• Benefits of exercise for bone and cartilage health.

Closing Remarks

• Remember lab schedules and requirements.
• Reach out with any questions or clarifications needed on lecture content.