MECHANICAL LOADS 

COMPRESSION pressing together or squeezing force on the body caused by a collision of forces.

TENSION Opposite of compression, a pulling apart force on the body by forces moving directly away from each other.

SHEAR is a cutting force that acts on the body by forces moving in opposite parallel direction of each other.

MECHANICAL STRESS (pressure) is the distribution of force within a body. This is quantified by the amount of force divided by the area over which the force acts.

• For example: What would happen if you hit a nail with a 100 pounds of force versus what would happen if you hit a round bar 6 inches in diameter.
• What is the difference of getting stepped on with a women's high heal shoe versus the heal of man's dress shoe.
• "Wolff's Law" explains why ends of bones are usually larger cross-section than the shafts (i.e., condyles of femur); and how lumbar are better adapted to handle the stress of weight bearing.

BENDING FORCES ON BONES Due to compression on one side of bone while other side has tension.

TORSION - twisting of action around the long axis of a body. (e.g., twisting the cap off a jar or bottle is the effect of torsion forces; spiral fracture of the tibia is likely the result of torsion forces)

COMBINED LOADING the acting of multiple forces on the bone at the same time (i.e., torsion, compression, tension, shear, bending)