Introduction to Biomechanics

Force

• Push or pull that produces displacement

• External agent enabling body to change direction and be at a state of motion from rest

• Contains magnitude and direction

Kinesiology

• Study of motion and the internal and external forces involved in movement

• Art and science of movement

Anatomy

• study of structures of human body

Biomechanics

• human body + mechanics (study of forces and motion applied to a certain thing)

• study of forces and motion applied to human body

• Application of kinematics and kinetics to the mechanics of human movement

Statics

• study of objects that are either at rest or in constant motion

Dynamics

• study of objects that involve acceleration

Kinetics

• Study of forces and their impact on motion

• Study of motion that involves forces

Kinematics

• Study of motion WITHOUT regard to forces

Arthrokinematics

• concerned with the movement of 2 articulating joint surfaces

Osteokinematics

• movements of bony levers through their ranges of motion

Planes

• Dimensions in which motion occurs

Axis

• Imaginary straight line around which rotary or angular movement occurs

• is perpendicular to the plane

Frontal / Coronal Plane

• Z-axis

• Divides the body into front and back

Sagittal / Vertical Plane

• X-axis

• Divides the body into right and left

Horizontal / Transverse Plane

• Y-axis

• Divides the body into upper and lower

Center of Gravity

• intersection of the center of all three of these planes

• theoretical point which mass of object is balanced

• Where gravity acts

S2

• level of center of gravity for adults

Stable

• line of gravity is within the base of support

Unstable

• line of gravity is outside the base of support

Degrees of Freedom

• Number of planes a joint moves at

• Determined by the type of joint

Uniaxial

• 1 degree of freedom

Biaxial

• 2 degrees of freedom

Triaxial

• 3 degrees of freedom

Uniaxial

• Hinge and Pivot joints

Biaxial

• Condyloid, ellipsoidal, and saddle joints

Triaxial

• Ball and Socket joint

Kinematic Chains

• A combination of several joints uniting successive segments

Open Kinematic Chain

• the DISTAL segment of the chain moves in space while the PROXIMAL is planted or stationary

Closed Kinematic Chain

• the PROXIMAL segment of the chain moves in space while the DISTAL is planted or stationary

Closed Pack Position

• Joint is compressed & difficult to distract

• Joint surfaces are mostly in contact.

• Ligaments and capsular structures are slack

Open Pack Position

• Ligaments are farthest apart and under tension

• Capsular ligaments are taut

• Joint surfaces may be distracted

• Allow motions such as spinning, rolling, & sliding

• Injuries are more common in this position

Sliding

• 1 joint surface is parallel to the plane of the adjoining joint surface

Spinning

• 1 point of contact on each surface remains in contact with fixed location on another surface

Rolling

• Each point on 1 surface contacts a new point on the other surface

20° of extension of the knee

• when rolling, sliding, and spinning occurs

Opposite (1st Concave-Convex Principle)

• If the bone with the convex joint surface moves on the bone with the concavity, the convex joint surfaces move in the ___ direction to the bone segment

Same (2nd Concave-Convex Principle)

• If the bone with the concavity moves on the convex surface, the concave articular surface moves in the ______ direction as the bone segment.

Isokinetic

• Occurs when rate of movement is constant

• Only happens when we use machines

• same speed

Isometric

• static/holding contraction

• no change in joint angle

• same length

Isotonic

• constant tension as muscle length changes

• same tone

Eccentric

• muscle lengthening

Concentric

• muscle shortening

Levers

• a simple machine made of a rigid bar rotating around a fulcrum.

Mechanical Advantage

• Ratio between the length of the force arm and the length of the resistance arm

• Greater mechanical advantage = task is easier to accomplish

1st Class Lever

• Exerted force on opposite sides of the axis or fulcrum

• aka “EFW”

• MA = 1

2nd Class Lever

• Weight/resistance is situated in between effort force and axis

• Aka “FWE”

• MA = >1

3rd Class Lever

• Effort force is between axis and resistance force

• Aka “FEW”; most common

• MA = <1