Basic Concepts in Biomechanics Lecture 1 AC1101 Dr. J. Kim Ross

Definition  Biomechanics is the study of mechanics in the human body.  Why are we interested in biomechanics as chiropractors?  Because spinal manipulation is a biomechanical intervention!

Subdivisions of Biomechanics Biomechanics Kinetics Kinematics

Kinematics  The division of biomechanics that describes motion without consideration of the forces that cause the motion.

Kinetics  The division of biomechanics that is concerned with the forces producing motion or maintaining equilibrium

Kinematics  The kinematic variables include:  1) Types of Motion  2) Location of Motion  3) Direction of Motion  4) Quantity of Motion

1) Types of Motion  A) Rotatory (Angular) Motion  B) Translatory (Linear) Motion  C) Curvilinear Motion  D) General Plane Motion

A) Rotatory (Angular) Motion  Movement of a segment around a fixed axis in a curved path.  Each point on the segment moves through the same angle at the same time at a constant distance from the axis of rotation  Few joints if any move around a truly fixed axis  However they are often described as though they do.

Figure 1. Angular Motion. When this arm moved from horizontal (white) to a 45 degree angle (red), all points on that arm moved through the same angle but clearly point B traveled a greater distance. A A B B A A) Rotatory (Angular) Motion

B) Translatory (Linear) Motion  Movement of a segment in a straight line.  Each point moves through the same distance at the same time in parallel paths.  Occurs when one bone is pulled away from or pushed toward it’s joint.  When one flat contiguous joint surface translates along another, this is also translatory motion and is referred to as gliding.

B) Translatory (Linear) Motion  Eg of translatory motion external to a joint is forward movement of the hand and forearm.  The movement is actually produced by rotation at both the elbow and shoulder joints.

A C B C B A Figure 2. Linear Motion. When this box was moved from left to right each point on the box moved the same distance (note that the three arrows are the same length. B) Translatory (Linear) Motion

C) Curvilinear Motion  Rotatory and translatory motion combined.  Rotation around a joint is accompanied by gliding of the articular surfaces.  This produces a moving axis and therefore curvilinear action.  This is the most common form of motion produced at a joint.  Gliding is slight and hence motion described as though it was pure rotation.

D) General Plane Motion  Object rotates about an axis while the axis is translated in space by motion of another segment.  Forearm rotates around the elbow as the elbow joint is translated by the upper arm.

2) Location of Motion  A) Transverse Plane  B) Frontal (Coronal) Plane  C) Sagittal Plane

A) Transverse Plane  Divides the body into upper and lower halves  Movement in this plane occurs parallel to the ground.  Eg. Movement of the nose when rotating the head.

B) Frontal (Coronal) Plane  Divides the body into front and back halves.  Eg. Bringing the ear to both shoulders requires the head to move through a frontal plane.

C) Sagittal Plane  Divides the body into left and right halves.  Eg. Nodding the head as if to indicate yes requires sagittal plane motion.

3) Direction of Motion  A) Flexion  B) Extension  C) Abduction  D) Adduction  E) Medial (Internal) Rotation  F) Lateral (External) Rotation  G) Compression  H) Distraction

A) Flexion  Refers to rotation of a body segment around a joint axis so that the ventral surfaces are being approximated.  Exception is the Knee and Foot  During development the surfaces rotate 180 degrees  Sagittal plane motion

B) Extension  Refers to rotation of a body segment around a joint axis so that the dorsal surfaces are being approximated.  Sagittal plane motion

C) Abduction  Rotation of a segment around an axis so that the distal segment moves away from the midline of the body.  Occurs in the frontal plane

D) Adduction  Rotation of a segment around an axis so that the distal segment moves towards the midline of the body.  Occurs in the frontal plane

E) Medial (Internal) Rotation  Motion in the transverse plane around a longitudinal axis toward the midline of the body.  If the segment is part of the midline of the body (ie. the spine) then the rotation is simply termed left or right rotation. The designation is with respect to the anterior portion of the body.

F) Lateral (External Rotation)  Motion in the transverse plane around a longitudinal axis away from the midline of the body.

G) Compression  Translatory motion of a segment toward it’s joint.

H) Distraction  Translatory motion of a segment away from it’s joint.

4) Quantity of Motion  A) Rotatory –Measured in degrees or radians  B) Translatory –Measured in inches or centimetres etc.