Basic Biomechanical Concepts

What systems make up the human movement system?

Musculoskeletal, nervous, cardiovascular, pulmonary, endocrine, and integumentary

Why is the human movement system considered a learning system?

Components produce movement and are influenced by a movement

How does movement affect the body?

Improves cardiovascular fitness, bone health, cognition, and is associated with lower dementia risk

What does kinesis mean?

Movement

What does -ology mean?

Study of; branch of knowledge

What disciplines contribute to kinesiology?

Anatomy, physiology, biomechanics, and neuroscience

What is biomechanics?

The study of how the body moves

What are the two major subdivisions of biomechanics?

Kinematics and kinetics

What is neuromuscular analysis?

Analysis of muscle activity using EMG

What is kinematics?

Description of motion without considering the forces causing it

What is kinetics?

The study of forces and torques that cause, modify, or prevent motion

Kinematics asks what question?

What is the motion?

Kinetics asks what question?

Why/how does motion occur?

What are the 5 kinematic variables?

Type of displacement

Location of displacement in space

Direction of displacement

Magnitude of displacement

Rate of change of displacement

What is translatory motion?

Linear displacement; movement of a segment in a straight line

Ex: wheelchair rolling forward

What is rotary motion?

Angular displacement; movement of a segment around a fixed axis

Ex: Knee extension while kicking a ball

Motion in the sagittal plane occurs around what axis?

Coronal (frontal) axis

What movements occur in the sagittal plane?

Flexion and extension

What is flexion?

Decreasing the angle between two body segments

What is extension?

Increasing the angle between two body segments

Motion in the frontal plane occurs around what axis?

Anterior-posterior (A-P) axis

What movements occur in the frontal plane?

Abduction and adduction

What is abduction?

Movement away from the midline

What is adduction?

Movement toward the midline

Motion in the transverse plane occurs around what axis

Vertical axis

What movements occur in the transverse plane?

Internal rotation, external rotation, right and left trunk/head position

What is internal (medial) rotation?

Rotation towards the midline

What is external (medial) rotation?

Rotation away from the midline

Rotary motion is measured in what units?

Degrees

What is ROM?

Range of Motion

Translatory motion is measured in what units?

Meters, feet, or inches

What is speed?

Displacement per unit time regardless of direction

What is velocity?

Displacement per unit time in a specified direction

What is acceleration?

Change in velocity per unit time

What are external forces?

Gravity, weight of an object, and external loads

What are internal forces?

Forces produced by muscles, ligaments, and bones

Are forces scalar or vector quantities?

Vector quantities

What is Newton’s First Law?

An object remains at rest or constant velocity unless acted upon by an external force

What is inertia?

Resistance to changes in motion; proportional to mass

What is Newton’s Second Law?

Force equals mass times acceleration

What is Newton’s Third Law?

For every action there is an equal and opposite reaction

What is a force?

A push or pull that can move an object or change its speed

What two components does every vector have?

Magnitude and direction

Through what point does gravity act?

Center of Mass (COM) or Center of Gravity (COG)

In what direction does gravity act?

Vertically downward toward the earth

What is the Center of Mass

The point where the body’s mass is considered concentrated

What is the Line of Gravity?

An imaginary vertical line extending downward from the Center of Mass

What increases stability?

Larger Base of Support and lower Center of Mass

What happens if the Line of Gravity falls outside the Base of Support?

Loss of balance occurs

What are the three components of a lever?

Axis (fulcrum), force (effort), and resistance (load)

First class lever arrangement?

Force-Axis-Weight

Examples of first class levers?

Head on neck; pelvis relative to hips

Second class lever arrangement?

Axis-Weight-Force

Examples of second class levers?

Heel raise and push up

Third class lever arrangement?

Axis-Force-Weight

What class of lever is most common in the human body?

Third class lever

Example of a third class lever?

Biceps curl at the elbow

What is torque?

The rotational effect of a force around a joint axis

What is a moment arm?

The perpendicular distance from the joint axis to the line of force

Longer momentum arm=?

Greater torque

Shorter momentum arm?

Less torque

Why does tendon insertion distance matter?

A tendon inserting farther from the joint produces more torque from the same muscle force

Why is a bicep curl hardest at approximately 90 degrees of elbow flexion?

Gravity is perpendicular to the forearm, producing the greatest moment arm and maximum torque

What is ground reaction force?

A reaction force provided by the supporting surface

What is friction?

A force that resists movement of an object

What is ligament force?

Resistance to destabilizing forces acting as a joint

What are elastic forces?

The tendency of a structure to return to its original length after being stretched

What is passive tension?

Stiffness resulting from elongation of non-contractile muscle components

What structures contribute to passive tension during a slight stretch?

Titin

What structures contribute to passive tension during a moderate-strong stretch?

Extracellular connective tissue, especially tendon

What is active muscle force?

A tensile force transmitted through a tendon to bone that may produce body segment motion

In clinical practice, what comes first: kinematics or kinetics?

Observe the kinematics (what happened), then use kinetics to explain why it happened

Why is muscle testing commonly performed around 90 degrees of elbow flexion?

Because the forearm is perpendicular to gravity, producing the greatest moment arm and maximum torque

What is a simple way to remember internal rotation?

Rotation toward midline (example: pigeon-toed position)

What is a simple way to remember external rotation?

Rotation away from the midline (example: duck-footed position)

Why is the human body considered mechanically disadvantaged?

Muscles often have short moment arms and must generate large forces to produce relatively small torques

What happens to required muscle force when the moment arm becomes shorter?

The muscle must generate more force to move the limb

What happens to required muscle force when the moment arm becomes longer?

Less force is required to generate the same torque

Through what point does gravity act on each body segment?

Through that segment’s Center of Mass (COM)

Why does torque change throughout range of motion?

Because joint angle and moment arm change throughout Range of Motion?

What do opposing muscle groups create?

Opposing torques