Biomechanics 2 Anatomy

support

Organs and tissues held in place

protection

vital organs

movement

base for muscle attachment

production and storage

manufacture red and white blood cells and store minerals

structure of skeleton

206 bones found in an adult skeleton, divided into two main groups: axial and appendicular

axial skeleton

Forms long axis of the body: Skull, vertebral column, and rib cage

Protection, support, and carrying other body parts

vertebral column

Divided into 5 main regions:

(1) Cervical spine (7)

(2) Thoracic spine (12)

(3) Lumbar spine (5)

(4) Sacrum (5)

(5) Coccyx (4)

The 5 sacrum vertebrae and 4 coccyx vertebrae are fused to form one solid bone.

Thorax

12 pairs of ribs. Joined to thoracic vertebrae. Top 10 ribs joined to sternum. Remaining two have free ends = ‘floating’

appendicular skeleton

Upper & lower limbs. Girdles (pectoral & pelvic). Locomotion and manipulation of the environment

pectoral girdle

2 scapulae: Articulates with humerus

2 clavicles: Articulates with sternum & scapula

upper limb

humerus, radius, and ulna

humerus

between shoulder and elbow

radius

lateral or thumb side

ulna

medial or little finger side

pelvic girdle

a ring of bone that articulates the lower limbs with the trunk, consisting of the two innominate bones and the sacrum, and it provides stability for weight transfer while supporting the pelvic viscera and facilitating muscle attachments.

Ilium, ischium, and sacrum

lower limb

femur (between hip and knee), patella, tibia (shin), fibula

foot

Ankle → 7 tarsals

Calcaneus forms heel

This: 5 metatarsals and 3 phalanges per digit

anatomical position

Standing erect, arms at side with palms anterior & thumbs lateral

sagittal

body plane that is from anterior to posterior. a vertical line that splits the body or organ into left and right sides

frontal/coronal

body plane that is from side to side. an imaginary vertical line that divides the body into front (anterior) and back (posterior) halves

horizontal/transverse

body plane that is front to back horizontally. an imaginary horizontal line that divides the body into upper (superior) and lower (inferior) halves

superior/cranial

above torso. toward the head

inferior/caudal

below torso. toward the feet

anterior

ventral - front.

posterior

dorsal - back

medial

toward the midline (inside)

lateral

toward the side (outside)

proximal

nearer the trunk

distal

further from the trunk

prone

face down (on stomach)

supine

face up (on back)

Flexion/Extension

sagittal plane. foot plantar flextion/dorsiflexion

pronation/supination

transverse plane. forearm/hand

abduction/adduction

coronal plane

inversion/eversion

opposite movements of the foot that turn the sole toward or away from the midline of the body

medial/lateral rotation

transverse plane. femus/humerus. movements of body parts around their long axis, where medial rotation is turning toward the center of the body and lateral rotation is turning away from it

circumduction

a conical body movement where the base of a limb or digit stays relatively fixed while the distal end describes a circle

protraction/retraction

opposite movements of the shoulder blades (scapulae). (1) moves the shoulder blades forward and away from the spine, causing the upper back to round. (2) pulls the shoulder blades backward and together toward the spine, opening up the chest.

elevation/depression

opposing movements in a superior (upward) or inferior (downward) direction

anthropometric data

systematic, quantitative measurements of the size, shape, and physical characteristics of the human body, needed to build models.

Empirical science concerned with physical static and functional/dynamic dimensions of human body

anthropometrics

Measurement of physical characteristics of humans. Measurement of body segment parameters. Examples of anthropometric variables? Needed for: Biomechanical analysis of postures, Development of biomechanical models

normal distribution

Most anthropometric variables are distributed this way. Other names: Gaussian or Bell distribution - defined by mean and standard deviation

histogram

variable on x-axis, & no. of individuals on y-axis

Normal distribution: symmetric shape histogram

percentile

Indicates percentage of distribution that is equal to or below it

assumptions in biomechanics

• Body segments behave like rigid bodies

• Modeling some parts of the body as one single body when they consist of several segments

• Validity at the scale of gross body movements

Measurement of Body Segment Link Length

Instruments: Anthropometer, Calipers, Tapes

Body Segment Link Length Data

Length_segment = Constant x Stature

methods for deriving BSP

Four general approaches

• Cadaver studies

• Mathematical modeling

• Scanning and imaging techniques

• Kinematic measurements

most recent studies use a combination of approaches

Cadaver studies

Inertial variables are somewhat difficult to determine for a living person. Coefficient method based on proportions of body mass and body height to predict body segment parameters

Example: Dempster (1955)

8 cadavers - Segments defined based on joint centers (see table 3.1)

See table 3.2 for variables that can be derived from coefficient method based on Dempster data.

other cadaver studies

Clauser et al. (1969), Handler (1975): Body segments defined using palpable bony landmarks instead of joint centers (see Table 3.3)

Additional number of cadavers compared to Dempster’s study

• 13 were used by Clauserre used by Chandler

• Results presented in tables similar to Dempster’s data (see Table 3.4)

mathematical modeling

Assumption: body segments can be modeled as geometrical shapes with constant distribution of mass

Geometrical shape

• Frustrum (most segments)

• Sphere (hand)

• Ellipsoid (head)

imaging techniques

Dual energy X-ray Absorptiometry (DXA)

kinematic techniques

Base BSP derivation based on kinematic characteristics

Oscillation technique- Hatze (1975)

• Segment mass, segment com, segment moment of inertia

• Body part set into oscillation with an instrumented spring

• Muscles must be relaxed so that they do NOT influence limb-spring system

• CanNOT be used on trunk

• Small oscillation theory to estimate segment parameters

moment of inertia

in kinematic techniques, this is estimated based on quick-release method.

Assume muscles are relaxed. Acceleration of a rapidly accelerated segment is affected by segment’s rotational inertia

segment mass

2D computational method example: Weigh subject and multiply total mass by appropriate proportion (P-value) for a segment of interest

center of mass

2D computational method example: Represent distances from proximal/distal ends to segment com as proportions (R-values) of segment length (l)

moment of inertia (rotational inertia)

Definition: resistance to rotational motion

Equivalent of mass in translational motion

Can be calculated using radius of gyration. Radius of gyration = k = how far the mass of a rigid body would be from an axis of rotation if its mass was concentrated at that point.

I_axis = ∫r²dm

radius of gyration

moment of inertia → compute this. Minimum when body rotates about own COG = centroidal moment of inertia.

the root-mean-square distance of an object's mass or cross-sectional area from a specific axis of rotation or centroidal axis

factors affecting measurements

• Ethnic origin: e.g. stature

• Gender: e.g. size, strength

• Age: e.g. disc compression & stature, e.g. reach, range of motion

• Disability: e.g reach, range of motion

anthropometry varies across populations and ethnicity

“If a piece of equipment was designed to fit 90% of the male U.S. male population, it would fit roughly 90% of Germans, 80% of Frenchmen, 65% of Italians, 45% of Japanese, 25% of Thais and 10% of Vietnamese”