Biomechanics Flashcards
Body components of biomechanics
1.) Bones
act as lever arms
2.) Muscles
pull on the bones (contract) to create motion or can
relax to move bones
3.) Joints
influence the degree of freedom of the movement
4.) Ligaments
passive restraint of joints
5.) Tendons
transfer force from muscle to bone
6.) Nervous system
feedback and control over muscles
Degrees of freedom of the spine
- three axises yeild 6 degrees of freedom PLUS ability to translate
translation
sliding along the transverse plane in infinite number of directions
What makes up a lever system
- Fulcum (joint)
- Applied force (muscle = effort)
- Resistance (weight of limb= load)
1st Class Lever
fulcrum is between the effort and the load
- trapezius, head, and neck
2nd class lever
fulcrum on the end, load in the middle, effort on the other end
- wheel barrow example
- Gastrocs
3rd class lever
fulcrum at one end, effort in the middle, load on other end
- elbow, biceps, load in hand
Which levers are faster?
Which are more powerful?
Class 1 and 2 are most powerful
Class 3 is fastest
Lever class most common in the body
Class 3
Where does the effort get distributed?
- Some to the load
- Some to the joint
Think of elbow example- get compression of the elbow joint
Moment arm in biological systems
perpendicular distance from the line of action of the muscle to the axis of rotation (joint)
- longer moment arm = more force (more mechanical advantage)
Line of pull
Not what a muscle attaches to but where it attaches that matters
**About how a muscle crosses a joint
Concentric contraction
muscle shortens and contracts (decrease in joint angle)
Effort exceeds resistance
Isometric contraction
Contraction occurs
No movement of the joint
Eccentric contraction
muscle lengthens and there is increase in joint angle
Resistance exceeds effort
Tone
Continuous low level contraction at all times (no true off)
Discuss the changes in moment arm as the elbow flexes and the ability of the bicep to create torque at elbow
- Strongest at 90 degree angle (all of the effort goes to moment arm, none to compression)
- Weakest when arm is straight ( getting more compression and shorter moment arm)
does movement only occur through stimulating contractions?
No- you can relax muscles to fall down on purpose
Length-Tension Relationship
- Changes in strength is due to length of a muscle
Tension
- two opposing pulling forces that stretch and object
Compression
- two opposing forces that push towards each other
squeezing IV disc
Shear
two opposing forces not inline with one another causing adjacent segments to move opposite
Torsion
-Twisting that causes one section to go clockwise and another section to go counter clockwise
Disc prolapse
- occurs during sudden compression coupled with flexion and lateral flexion (may include rotation)
Where does the highest frequency of spine injury occur? why?
T12-L1
has highest torsional stiffness (highest stress concentration)
Cervical trends of motion
- good rotation almost throughout
- good lateral flexion in the middle
- C5/C6 is the most mobile of all the vertebral column
Cervical Coupling
-lateral felxion and rotation work together
- rotation proceeds lateral flexion then both occur
together
Thoracic trends of motion
- flexion amount increases the more you go down
- Lateral flexion improves with floating ribs (T11)
- rotation lessens in lower thoracics ( Facet joints in the
saggital plane)
Lumbar trends of motion
- good flexion and extension in the lumbar region
- poor rotation throughout lumbar
