Biomechanics of

Musculoskeletal System

Strahinja Dosen, sdosen@hst.aau.dk

University of Novi Sad, Dec 2010

Biomechanics of Musculoskeletal System

Lecture 1: Human body: Basic anatomy and physiology

Lecture 2: Human movement recording

Lecture 3: Muscle modeling and simulations

Lecture 4: Musculoskeletal modeling and simulations

Lecture 5: Modeling for functional electrical stimulation

Lecture 1:

Human body: basic anatomy and physiology

Strahinja Dosen, sdosen@hst.aau.dk

1. Skeleton (bones, joints)

2. Tendons

3. Ligaments

4. Muscles (structure, properties)

5. Peripheral nerves and receptors

6. Central nervous system

Bones

• Mechanical functions

– Support

– Transfer forces (lever)

– Protection of internal organs

• Physiological functions

– Forming blood cells (hematopoiesis)

– To store calcium (mineral homeostasis)

NAME OF BODY “REGION" No of

Bones

VERTEBRAL COLUMN, SACRUM,

AND COCCYX

26

CRANIUM 8

FACE 14

AUDITORY OSCICLES 6

HYOID BONE, STERNUM AND RIBS 26

UPPER EXTREMITIES 64

LOWER EXTREMITIES 62

TOTAL 206

Bones

Bone Composition

• Connective tissue

• Biphasic (composite) material

(~fiberglass)

• Composition:

– Cells (osteocyte)

– Extracellular matrix of fibers (collagen)

– Ground substance (proteoglycans)

– Water (25 %)

– Mineral salts

Microscopic Structure

Macroscopic Structure

Frontal longitudinal section through the head neck, great trochanter, and

proximal shaft of the adult femur. Cancellous bone, with the trabeculae

oriented in a lattice, lies within the shell of cortical bone. (From 13th

American Ed. Of Anatomy of the Human Body, Philadelphia, 1985.)

Material testing

F/A

(L – Lo)/Lo

Bone characteristics

ANISOTHROPY

Loading modes

Bone Fractures

Bone Remodeling

JOINTS

JOINTS

Joints

Cartilage

• Transferring forces between bones

• Distributing forces (loads) in the joints

• Relative movement with minimal friction

• Highly specialized tissue

– Typical thickness (1 – 5 mm)

– Isolated tissue (without blood vessels, lymph

channels, nerves)

– Lowest cellular density

Cartilage Composition

• Biphasic (composite) material (~ stiff

sponge): fibrous organic matrix and tissue

fluid (60%, mostly water)

• Extracellular matrix of collagen fibrils

enmeshed in concentrated solution of

proteoglycans

• Cell (chondrocytes)

Microscopic Structure

Collagen

Microscopic Structure

Proteoglycan Aggregates

Macroscopic Structure

Viscoelastic Properties

Self-Lubrication

BOOSTED LUBRICATION

MIXED LUBRICATION

Wear of the Cartilage

Muscle, Tendon, Bone

Tendons

• Attach muscles to the bones and transmit

tensile loads from muscles to bone,

thereby producing joint motion.

• The tendon enables the muscle to act at a

mechanically optimal point that can be

very distant from the actual muscle body

Tendon composition

• Parallel-fibered collagenous tissue

• Cells (fibroblasts)

• Water (70%)

• Solid (30%):

– Collagen (>75%)

– Proteoglycans (much less then in cartilage)

Structure

Muscle – Tendon – Bone

OSTEO-TENDON JUNCTION

MYO-TENDON JUNCTION

Tensile Properties

Ligaments

• To attach articulating bones to one

another across a joint

• To guide joint movement

• To maintain joint congruency

Ligament Composition

• Very similar to tendons

Ligament – Bone Junction

Ligament Function

Ligament Properties

MUSCLES

Skeletal Muscle

Structure

Contraction

Contraction

Muscle fiber properties Length – Active Tension

Muscle fiber properties Length – Total Tension

Muscle fiber properties Velocity – Tension

Muscle fiber properties Velocity – Length – Tension

Muscle Activation – Twitch

Muscle Activation – Tetanus

Motor units

SIZE

The smallest motor units are in muscles that

must produce very fine gradations of force (e.g.,

lumbricals - 100 fib/unit, eye muscles - 5 fib/unit).

DISTRIBUTION WITHIN MUSCLE

The fibers which make up a motor unit are not

adjacent to one another, but they inhabit the

same general region of the muscle.

MOTOR UNITS ARE ORGANIZED

ACCORDING TO:

Motor unit types

MOTORNEURON /

MUSCLE FIBERS

Small diameter

motorneurons innervate

slow oxidative fibers.

Intermediate sized

motorneurons innervate

fast oxidative/glycolitic

fibers

Large diameter

motorneurons innervate

fast glycolitic fibers.

SIZE PRINCIPLE

Small diameter motorneurons

are more easily excited

compared with the large

diameter motorneurons.

Therefore:

1. Slow oxidative motor units

are recruited by relatively low

level of excitatory synaptic

input.

2. Fast glycolitic motor units

are recruited by high levels of

excitatory synaptic input.

SIZE PRINCIPLE

RECRUITMENT

•Flexion/extension

•Abduction/adduction

•Internal/External Rotation

(Medial/Lateral)

____________________

•Monoarticular muscles

(over 1 joint)

•Biarticular muscles

(over 2 joints)

•Multiarticular muscles

(over more than 2 joints)

SKELETAL MUSCLES

plexus

tendon

SKELETAL MUSCLES

Agonist – muscle primarily responsible for

the movement

Antagonist - muscle which opposes the

agonistic action

Synergist – muscle that assists the

agonistic action

Fixator – synerigistic muscle that assists

stabilization of the joint

SKELETAL MUSCLES

A

G

B

C D

E

H

F I

J

K

Muscles controlling the hip joint: medial rotation (left panel) and lateral rotation (right panel). A) Gluteus Medius m. and Gluteus Maximus m; B) The Tensor Fascia Latae m; C) Adductor Magnus; D) Gluteus Minimus m. and m; E) Illipsoas m; F) Gluteus Maximus m; H) Gracilis m; G) Pectineus m; I) Piriformis m; J) Quadratus Femoris m; K) Obturator Internus m.

SKELETAL MUSCLES

Muscle, Tendon, Bone

PERIPHERAL

NERVES

MAIN BRANCHES OF RADIAL NERVE

BRANCHES OF MUSCULO-CUTANEOUS, MEDIAN & ULNAR N.

SUPERFICIAL BRANCH OF

ULNAR N.

DEEP BRANCH OF ULNAR N.

ULNAR N.

MEDIAN N.

CUTANEOUS NERVES

BRACHIAL N. PLEXUS

AXILARY N.

RADIAL N.

DORSAL DIGITAL N.

DEEP BRANCH OF

RADIAL N.

SUPERFICIAL BRANCH OF RADIAL N.

PERIPHERAL

NERVES

Main branches

of radial nerve

(left), and

median and

ulnar nerves

(right).

COMMON

PERONEAL N.

PUDENTAL N.

FEMORAL N.

SCIATIC N.

LUMBAR

PLEXUS

SACRAL

PLEXUS

TIBIAL N. DEEP PERONEAL N.

SUPERFICIAL

PERNOEAL N.

LATERAL SURAL

CUTANEOUS N.

SAPHENOUS N.

LATERAL FEMORAL

CUTANEOUS N.

MEDIAL AND LAT.

PLANTAR N.

PERIPHERAL

NERVES

MUSCLE

TENDON

TENDON

GAMMA MOTOR

NEURON

GOLGI TENDON

ORGAN

AFFERENT

GOLGI TENDON

ORGAN

ALFA MOTOR

NEURON

EXTRAFUSAL

MUSCLE

FIBER

INTRAFUSAL MOTOR

NEURON (MUSCLE

SPINDLE)

PRIMARY

SPINDLE

AFFERENT

SECONDARY

SPINDLE

AFFERENT

FREE

NERVE

ENDING

The muscle spindles (intrafusal fibers) are in

parallel with the extrafusal fibers; the Golgi

tendon organs are in series. The intrafusal

fibers attach actually to the extrafusal fibers, not

to the tendons

PERIPHERAL NERVES

PERIPHERAL NERVES

Control loops

Lateral view of the spinal cord and its location in the spinal canal.

CERVICAL

CORD

THORACIC

CORD

LUMBAR

CORD

SACRAL

CORD

THORACIC

NERVES

CERVICAL

NERVES

LUMBAR

NERVES

SACRAL

NERVES

LUMBOSACRAL

ENLARGEMENT

SPINAL CORD

DORSAL COLUMN

INTERMEDIATE

ZONE

DORSAL MEDIUM

SEPTUM DORSAL INTERMEDIATE

SEPTUM

ZONE OF LISSAEUR

VENTRAL COLUMN

VENTRAL MEDIAN

FISSURE

WHITE MATTER

GRAY MATTER

DORSAL

ROOT GANGLION

DORSAL HORN

VENTRAL HORN

The white matter of the spinal cord is divided into columns, and the gray matter is divided into horns. The Roman numbers show laminae divided

in three major divisions.

SPINAL CORD

DORSOLATERAL

CELL GROUP

INTERMEDIATE ZONE

MOTOR NEURON POOL

TO AXIAL MUSCLES

VENTROMEDIAL

CELL GROUP MOTOR NEURAL POOL TO

LIMB MUSCLES

VENTRAL ROOT

DORSAL HORN

VENTRAL HORN

DORSAL ROOT

GANGLION

Input-output organization of spinal segments and interconnections between segments.

DORSAL ROOT

Central Pattern Generator • Basic rhythm

• Variable response

• Evidence from non-primates

• Local or distributed

• Single-cell or network

SPINAL CORD

THE SPINAL CORD / INTEGRATION &

CINNECDTIVITY

The spinal cord has a lot of clockwork that can be mixed

and matched to perform tasks (This was mostly

postulated by Sherington – reflex)

The brain learns to perform tasks by iteratively optimizing

its use of the spinal clockwork (Optimal control is

inevitable)

Some strategies take more practice and knowledge of

results to discover (coaches can help avoiding local

minima)

No brain ever foregoes a potentially useful strategy to

validate a pet theory (motor physiology tends to be

mechanically inevitable of experimentally falsifiable)

The major division of the central nervous system. The top portion is a cerebral hemisphere. The parts are: cerebral hemispheres, diencephalon, midbrain, pons, medulla and spinal cord.

ACTIVITY OF CORTICAL REGIONS - fMRI

The lateral view of the cerebral cortex of the left hemisphere.

ACTIVITY OF CORTICAL REGIONS - fMRI

HOMUNCULUS (Rasmunsen, 1950)