1. Forces and Classes of Levers in the body

2. Types of forces Compressive – squeezing force from weight- bearing and gravity Long bones can withstand 25,000 psi of compressive force in the longitudinal direction

3. Types of forces Tensile – what happens with physical activity when muscles or tendons pull on bones at attachment sites, creating movement or increasing stability knee flexion created tension on the tibial tuberosity

4. Types of forces Tortion- the twisting effect Can be beneficial or harmful standing on your tibia and turning (beneficial) excess twisting of an arm causing a spiral fracture (harmful)

5. Types of forces Shear – tearing across the longitudinal axis, combating momentum Sudden stopping Long bones can only withstand 7 psi of force in the horizontal direction.

6. Lever Systems 1 st class: fulcrum is between the force (effort) and resistance

7. Lever Systems 2 nd class: resistance is between the fulcrum and the force (effort)

8. Lever Systems 3 rd class: the most common in the body- where the force (effort) is placed between the fulcrum and the resistance

9. Maintaining Healthy Joints Requires 3 Properties of Levers: Equilibrium- state of zero acceleration, no change occurs in speed or direction of body. Balance- ability to control equilibrium, either statically or dynamically 1 st to go when aging Stability- resistance to change in body’s acceleration 2 nd to go when aging