Exam 1

biomechanics

the study of the mechanics of living things

- combines biology and physics

three ways to prevent injuries

1) identify risk factors

2) analyze movement to calculate risk

3) understand how forces interact

ways to minimize biomechanical stressors

identify and mitigate stressors associated with

- manual handling

- lifting

- pushing

- pulling

- any physical movement

ways to prevent musculoskeletal disorders

identify risk factors

- repetitive motions

- forceful exertions

- awkward postures

- prolonged static loading

Newton's first law of motion

an object will remain at rest of in uniform motion in a straight line unless acted upon by an external force

- "law of inertia"

ex) starting a sprint or balance while standing

Newton's second law of motion

the acceleration of an object is directly proportional to the force applied to it and inversely proportional to its mass

- "law of acceleration"

- F = ma

ex) jumping or throwing a ball

Newton's third law of motion

for every action, there is an equal and opposite reaction. when one object exerts a force on another, the second object exerts an equal and opposite force on the first

- "action, reaction"

ex) walking, running, or swimming

force

a push or pull, exerted by one object on another

- interactions between objects that cause change in motion or shape

- characterized by magnitude/strength, direction, and point of application

- external (gravity, moving cars) or internal (pull of a muscle, ligamentous resistance)

- F = ma

contact force

where two objects physically touch each other

non-contact forces

where two objects do not physically touch each other

ex) gravitational or electromagnetic forces

types of forces

- gravity

- muscle force

- ground reaction force

- joint contact force

- frictional force

- tension and compression

- shear force

- fluid force

ground reaction force (GRF)

the forces that act on the body as the result of its interaction within the ground

- equal and opposite in direction and magnitude to the force the body applies to the ground

ground reaction force vector

the vector representing ground reaction force

- where it passes in relation to the body indications what "moment" will occur at that joint

tension force

collinear forces acting in opposite directions to stretch or pull apart

compression force

loading, collinear forces acting in opposite directions

- the act of pressing together

shear force

a force acting parallel to the surface of an object

torsion force

a force that twists a body

effects of force on the body

- motion

- stability

- injury risk

- performance

- structural adaptation

acceleration of gravity

9.8 m/s^2

kinematics

descriptors of motion

ex) joint angle, velocity, planes of motion, direction

kinetics

forces causing motion

ex) ground reaction force, force of bat on ball

moment

the measure of the tendency of a force to produce rotation about an axis (an instant of torque)

- the rotational effect of a force around an axis or pivot point

- moment = force x distance

- unit is Newton-meters (Nm)

moment arm

shortest distance from an action point (end of the lever) to the joint center

torque

measure of the degree to which a force causes an object to rotate about an axis

- T = Fd

- rotational force that produces torsion or rotation around an axis

- interchangeably with moment

- used mostly with joints and muscles

first class lever

two forces on either side of the axis with the fulcrum in the middle

- see-saw

second class lever

resistance force is in the middle with effort force and fulcrum on either side

- wheelbarrow

third class lever

both effort force and resistance force are on the same side of the fulcrum

kinetic chain

a series of rigid links or segments (bones or body parts) interconnected by a series of joints

open kinetic chain

a kinetic chain in which one end of the chain is "free" to move in space so that one segment may occur independently of the other segments

closed kinetic chain

a kinetic chain in which the end of the chain is fixed (on the ground, on a door handle, etc). motion of one link in the chain will cause motion at all other joints

center of mass

single point of a body about which every particle of its mass is equally distributed

- the point at which the force of gravity may be considered to act

- approximately 1/2" anterior to S2

line of gravity

action line of the force of gravity, vertically acting on the center of mass

base of support

the area formed under the body by connecting with one continuous line all points in contact with the ground

balance

maintaining the line of gravity within the base of support

stress

the intermolecular resistance within a body to the deforming actions of an outside force

- stress = force / area (N/m^2)

strain

deformation, or change in dimensions of a body as a result of the application of a force

stress strain curve

E = Young's modulus (modulus of elasticity) = slope of the curve (stress over strain)

- material's stiffness

- the higher the modulus of elasticity, the less deformation under load

elastic phase

material has undergone force, but still returns to its original shape after removing the force

plastic phase

material has undergone force, and can no longer return to original shape after removing the force

- material has "yielded"

yield strength (point)

the stress at which a material begins to deform plastically

Wolff's law

bone strength increases and decreases as the functional forces on the bone increase and decrease

remodeling

mechanical strain (deformation) causes the bone to change in shape and strength

avulsion fracture

tendon or ligament pulls a small chip of bone away from the rest of the bone

- tensile loading

- tendons are stronger in tension than bones

ex) explosive throwing or jumping

five functional units of the upper extremity

1) shoulder girdle

2) shoulder joint

3) elbow

4) wrist

5) hand

shoulder girdle

clavicle and scapula

- articulates with the torso, humerus, and sternum

- sternoclavicular joint

- acromioclavicular joint

- coracoclavicular joint

motions at the shoulder girdle

- elevation

- depression

- upward rotation

- downward rotation

- protraction

- retraction

shoulder girdle elevation

levator scapulae and upper trapezius

shoulder girdle depression

pectoralis minor

shoulder girdle upward rotation

lower trapezius

shoulder girdle downward rotation

rhomboids

shoulder girdle protraction

serratus anterior

shoulder girdle retraction

rhomboids and middle trapezius

stabilizers

large muscles to protect unstable joint

- very small areas of articulation

- lots of mobility

- creates a stable base for the other muscles to pull from

movers

muscles that move the body

- shoulder girdle initiates most upper extremity activities

ex) over arm throwing - after torso motion, shoulder protraction initiates and contributes to speed of the throw

shoulder joint

articulation of the glenoid fossa with the head of the humerus

- glenohumeral joint

- very unstable due to shallow socket --> depends on rotator cuff muscles for stability

- most compromised joint in the body

motions at the shoulder joint

- flexion

- extension (deltoid)

- abduction (supraspinatus)

- adduction (infraspinatus)

- horizontal abduction

- horizontal adduction

- internal rotation

- external rotation (deltoid)

rotator cuff muscles

S - supraspinatus

I - infraspinatus

T - teres minor

S - subscapularis

- all originate on scapula and attach on head of humerus

- stabilizer for shoulder joint

shoulder joint movers

- deltoid

- coracobrachialis

- pectoralis major

- latissimus dorsi

- teres major

- biceps

- triceps

shoulder joint abduction

occurs at the glenohumeral joint, acromioclavicular joint, sternoclavicular joint, and scapulothoracic joint

- the first 120° is glenohumeral abduction (last 60° is all scapular upward rotation)

- at a certain point, the clavicle stops elevating and posteriorly rotates

supraspinatus

first move of shoulder abduction

- gets the humerus rolling in the glenoid fossa before the deltoid takes over

rotator cuff injuries

rotator cuff impingement syndrome or subacromial impingement syndrome

- almost always supraspinatus (location under the acromion)

- more about the tendons than the muscles --> tendons become stretched and can no longer hold the humeral head in the glenoid fossa, deltoid muscle pulls the head up too high in abduction --> impingement

- people with narrowed space between acromion and humerus are predisposed

- friction = irritation, inflammation, and wear

shoulder dislocation

glenohumeral joint is most commonly dislocated joint in the body

- shallow fossa and loose structure

- extreme mobility, but little surface area

- usually due to an outside force (accident)

motions at the elbow

- flexion

- extension

- pronation

- supination

elbow flexion/extension

occurs at humeroulnar joint

- most stable in close packed position of full extension

- door hinge (very simple)

what class lever is the biceps?

third class lever

what class lever is the triceps?

first class lever

elbow pronation/supination

occurs at radioulnar joint

- radius rolls medially and laterally over ulna

- annular ligament binds the head of the radius to the radial notch of the ulna

ulnar collateral ligament (UCL) sprain

UCL resists valgus stress at the elbow

- caused by overuse and microtearing

ex) high velocity/force throwing motions

tommy john surgery

- palmaris longus or hamstring tendon harvested

- holes drilled through humerus and ulna

- tendon is threaded through