INTRO TO BIOMECHANICS

1. by
Saifullah Khalid
(Lecturer)
School of Physiotherapy,
IPM&R, Dow University of Health
Sciences, Karachi09/29/16 1

2. Objectives
 After completion of this lecture the
student should be able;
1. To know the basic definition of
biomechanics
2. To know the types of biomechanics
3. To know the basic terms of biomechanics
4. To know that why biomechanics is
important to study?
5. To know about the brief clinical
applications of biomechanics
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3. Human BiomechanicsHuman Biomechanics
BiomechanicsBiomechanics
Mechanics
Structure
Function
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4. What Is Biomechanics?
 Biomechanics;
 “ The application of mechanical principles in the study ofThe application of mechanical principles in the study of
living organismsliving organisms ”
Involves the principles of anatomy and physics in the
descriptions and analysis of movement.
 The study of biological structures, processes and
functions by applying the methods and principles of
mechanics
BioBio == LivingLiving
MechanicsMechanics == Forces & EffectsForces & Effects
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5. Why Study Biomechanics?
 The purpose of studying Biomechanics is;
 To understand the forces acting on the human
body
 To manipulate these forces in treatment
procedures so that human performance may be
improved and further injury may be prevented.
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6. Why Study Biomechanics?
 Better understanding of both joint function and
dysfunction
 Design improvements in devices e.g. joint
arthroplasty systems and orthotic devices
 To understand how the musculoskeletal system
functions
 Useful in patient evaluations and treatments
 Important for clinicians such as orthopaedic
surgeons and physical and occupational
therapists
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7. Kinematics
 Kinematics …
Description of motion (e.g. how fast, how high, etc.)
without consideration given to its mass or the forces
acting on it.
 This may include …This may include …
 The movement of a single point on the body (e.g.
COG)
 Position of several segments (e.g. the Upper
Extremity)
 Position of a single joint
 Motions that occur between adjacent joint surfaces
 Kinematics examines how, when, and where a body
moves
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8. Types of Kinematics
 Arthrokinematics ……
 The movements occurring
between joint surfaces in
relation to the direction of
movement of the distal
extremity of the bone
 Osteokinematics …….
 Concerned with the movements
of the bones
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9. Kinetics
 Kinetics …..
 The study of forces that lead to produce, stop or modify
motions of the body
 It examines ……It examines ……
 The causes of motion
 The internal and external forces that cause motion or
cause a body to remain at rest
 The interactions between these forces
 Forces affecting motion …..Forces affecting motion …..
 Gravity
 Muscle tension
 External resistance
 Friction
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10. Types of Kinetics
 Statics…..
 Refers to situations where the body or object remains
at rest, or is moving at a constant speed in a state of
equilibrium.
 EquilibriumEquilibrium is a balanced state in which there is no
acceleration
 Dynamics...
 Deals with the changes in motion (acceleration)
brought on by unbalanced forces
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11. Arthrokinematics
 When a joint moves, three types of
motion can occur between the two
articulating surfaces
 Rolling or Rocking
 Sliding or Gliding
 Turning or Spinning
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12. Arthrokinematics
 In a pure rolling motionIn a pure rolling motion …………
 Each subsequent point on one surface contacts a
new point on the other surface
 In sliding and spinning ……In sliding and spinning ……
 the same point on one surface contacts new
points on the mating surface
 Most normal joint movementMost normal joint movement has some
combination of rolling, sliding and spinning
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13.  The knee jointThe knee joint …………
 Shows the combination of
these movements most
clearly
 If there were only a rolling
of the condyles of the femur
on the tibial plateau, the
femur would roll off the tibia
and the knee would dislocate
ArthrokinematicsArthrokinematics
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14. Arthrokinematics in
Sit To Stand
 Rising from a Seated to aRising from a Seated to a
Standing Position ……..Standing Position ……..
 the femur is extended on the
fixed tibia, the femoral
condyles roll and slide so that
they are always in contact with
the tibial condyles
 In the last part of knee
extension, the femur spins
(internally rotates on the tibia)
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15. Clinical importance of
Arthrokinematics
 Arthrokinematics (combination of Roll, Slide and(combination of Roll, Slide and
Spin) ……Spin) ……
 Permits a Large ROM while using a Small Articular
Surface
 If joints possessed only one of these motions ……..If joints possessed only one of these motions ……..
 The ROM would be limited
 The Larger joint surfaces would be needed to
accomplish the same ROM
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16. Kinematic Chains
 A kinematic chain refers to a series
of articulated segmented links,
such as the connected pelvis,
thigh, leg, and foot of the lower
extremity (Lower Kinematic Chains )
 Open Kinematic Chain
 the distal segment of the chain moves
in space while the proximal segment is
fixed or stable
 Closed Kinematic Chain
 the distal segment is fixed, and
proximal parts move09/29/16 16

17. A Squat is an example of
an close-chain motion
A leg curl from sitting
in a chair is an example
of an open-chain motion09/29/16 17

18. Kinematic Chains Activities
 Reaching or bringing the hand to the mouth …….
Open - Chain Motion
 Performing a chin-up …….. Closed - Chain Motion
 Standing to Sit …….. Closed - Chain Motion
 Sitting down in a Chair …… Closed - Chain Motion
 The leg moves forward on the fixed foot (dorsiflexion)
 The thigh approaches the leg (knee flexion)
 The thigh approaches the pelvis (hip flexion)
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19.  Walking and Stair Climbing ……………. alternation
of closed-chain motion and open-chain motion
 Standing from a Chair………. When a person uses theuses the
armrest of a chair to assist in coming to the standingarmrest of a chair to assist in coming to the standing
positionposition, the hand is fixed and the forearm moves in
relation to the hand, the arm moves away from the
forearm, and the arm moves toward the trunk
 Crutch-walking ……… the arms are fixed and the
body moves in relation to the arms ( Close – Chain
activity )
Kinematic Chains ActivitiesKinematic Chains Activities
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20. Sitting Down in a chair
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21. Arthrokinematic Relative to the
Osteokinematics
 Convex-Concave Relationships ………..
 If the bone with the convex joint surface moves on the
bone with the concavity, the convex joint surfaces move
in the opposite direction to the bone segment ………….
Shoulder Movements
 If the bone with the concavity moves on the convex
surface, the concave Articular surfaces moves in the same
direction as the bone segment ………………………….
Knee Movements
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22. Examples
 Shoulder Abduction …….
 A downward motion of the humeral head on the Glenoid
Cavity occurs when the humerus is moving upward
 Handstand ……..
 An upward movement of the glenoid on the humeral head
occurs when the scapula is moving ( Closed Kinematic
Chain )
 Knee Extension ……..
 An anterior movement of the concave tibial plateau on
the femur occurs during anterior movement of tibia
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23. Convex - Concave Principle
Example
Normal
Interphalangeal
Joint Movements
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24. Close-Packed and Open-Packed Positions
 The ovoid surfaces of joint pairs match each other
perfectly in only one position of the joint. This point of
congruency is called the Close -packed position
 This position usually occurs at one extreme in the range
of motion e.g. ………..e.g. ………..
 Elbow, Wrist, Hip, and Knee JointsElbow, Wrist, Hip, and Knee Joints …….. Full extension
 Ankle JointAnkle Joint ……………..Dorsiflexion
 MP JointsMP Joints …………. Flexion at the
 In all other positions, the ovoid joint surfaces do not fit
perfectly but are incongruent and called Open - packed
position or Loose - packed position09/29/16 24

25. Close-Packed Position VS.
Open-Packed Position
Close-Packed Position
 The maximum area of
surface contact occurs
 The attachments of the
ligaments are farthest apart
and under tension
 Capsular structures are
taut ( under tension)
 The joint is mechanically
compressed and difficult
to distract
Open-Packed Position
 The ligamentous and
capsular structures are slack
 The joint surfaces may be
distracted several
millimeters
 This position allows the
necessary motions of spin,
roll, and slide and may
decrease joint friction
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26. Mechanical Advantage of
Close-Packed Position
 Provides Great mechanical stability to the joint
 Reduces the need for muscle forces to maintain a position
for example;for example;
 Standing PositionStanding Position …………………………During standing, the hips
and knees are in their close-packed positions.
This permits erect standing with little or no contraction of
the muscles of the hips or knees and results in an
economy of energy expenditure
 Gripping Action …………….Gripping Action ……………. At 90 degrees of flexion,
the MPJs are in their close-packed positions. This
provides Mechanical advantage in gripping action09/29/16 26

27. Accessory Motions
 ln addition to angular motions (flexion or
abduction) joint surfaces can be moved
passively a few millimeters in translatory
motion, called accessory movements or joint
play
 ExamplesExamples ………..………..
 Distraction of joint
 Lateral glide
 Anterior-posterior glide
 Rotation
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28. Accessory Motions
 These are the passive movements applied by an examiner
 These motions cannot be performed voluntarily by the
subject
 Require relaxation of muscles
 Essential for normal pain-free joint function
 Performed by physical therapists inPerformed by physical therapists in ………………………………
 Assessment of the integrity of joint structures (e.g. In
Ligament Injury, there is excessive accessory motion
………. hypermobile joint )
 Joint mobilization techniques in the treatment of
hypomobile or painful joints ( e.g. In limited IP Joint
flexion, downward glide should be applied close to the
joint and in the line of normal joint surface movements)09/29/16 28

29. Clinical Consideration
 If the necessary distal movement of the head of the
humerus on the glenoid fossa were not present,
elevation of the arm would be severely restricted
…………………………. frozen shoulder
 The greater tuberosity may strike the acromion process
instead of sliding beneath it. Striking the acromion
process (and adjacent soft tissues) would produce
additional injury and pain ….………. impingement
syndrome
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30. End-Feel of Range of Motion
 When a normal joint is moved passively to the end of its
ROM, resistance to further motion is felt by the examiner.
This resistance is called the End-feel or The Physiologic
End-feel
 This is described as Hard, Firm or Soft End-feels
 Normal End-feelNormal End-feel …………….…………….
 Hard or Bony End-feel: when the motion is stopped by
contact of bone on bone, as in elbow extension
 Firm or Springy End-feel: when the limitation is from
ligamentous, capsular, or muscle structures, as in wrist
flexion
 Soft End-feel: when the motion is stopped by the contact
of adjacent soft tissues, as in full flexion of elbow
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31. Pathologic end-feel
 An end-feel that is not characteristic of the normal joint
End-feel and occur at a different place in the ROM of a
joint
 Empty End-feelEmpty End-feel …….……. Pain on motion but absence of
resistance associated with infection, active inflammation
and tumors
 Hard end-feel …….Hard end-feel ……. bony blocking as in Arthritic joints
 Springy end-feelSpringy end-feel ………………rebound feel at the inner of ROM
as in torn meniscus blocking knee extension
 Sudden Hard-feelSudden Hard-feel …......…...... Spasm of muscles
 Capsular feelCapsular feel ………………a hardest arrest of movement
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