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Human Motion
Objectives： After studying this topic, the students will be able to
- identify types of motions experienced by the human body
- explain the interrelationship between displacement, velocity, and
acceleration, and use the knowledge of this interrelationship to describe and analyze motion
- distinguish the angular kinematics from linear kinematics and describe their relationship
Definition of Motion
Types of Motions
Kinematic Description of Motion
Factors That Modify Motion
- Neumann, DA (2002)： Getting Started. in Neumann DA (ed)：
Kinesiology of the Musculoskeletal System - Foundations for Physical Rehabilitation.
Philadelphia： Mosby. pp.4-8
- Luttgens, K. & Hamilton, N., 2002 Chap11, pp.277-300
Definition of Motion
Motion
the act or process of changing place or position of a body
with respect to some reference point (Luttgens & Hamilton, 2002, p.284)
Rest vs. Motion
whether a body is at rest or in motion depends on the reference point
the trunk segment during standing up from a chair is in motion if the reference point is the foot
a sleeping passenger in a smoothly moving bus is at rest if the reference point is the bus
whereas it is in motion if the reference point is the ground
a parked car is at rest if the reference point is the earth
whereas it is in motion if the reference point is the sun
Absolute vs. Relative motion
absolute motion： using the global reference system
relative motion： using the local reference system
Newton's Law
Law of Inertia
Law of Acceleration： F = ma
Law of Reaction
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Types of Motions
Classification based on path of motion
translatory motion
(linear motion,
translation)：
a motion in which all parts of the moving body
move toward the same direction
rotary motion
(angular motion,
rotation)：
a motion in which the object acts as a radius and all parts of the moving
object rotate in the same angular direction and follow a circular path about a pivot point
angular motion：
the rotary motion with one side of the moving object fixed,
e.g. rotation of a limb
spin：
the rotary motion with the axis of rotation
around the center of mass
Classification based on repetition of motion
single motion： movement performed only once
repeated motion： same movement pattern that is done many times in a given time
reciprocal motion
oscillation： repeated motions in a small amplitude
pendulum motion： repeated motions like a pendulum
Classification based on degree of freedom
degree of freedom
(DOF)： a minimum number of kinematic variables required to specified all positions and
orientations of the segments in a body system i.e.
the number of planes in which the segments move
the number of the primary axes
which the segments possess
Examples:
The joint that moves in one plane possesses one axis and has one degree of freedom
For the glenohumeral joint, there are three angular degrees of freedom and three linear degrees of freedom.
Classification based on relative segment kinematics
kinematic chain：
a series of connected segment links
open kinematic chain motion：
the joint motion with the distal segment moves free in space,
e.g. raising lower leg or throwing a ball
closed kinematic chain motion：
the joint motion with the distal segment is fixed,
e.g. standing up or squatting down
In Neumann's book,
"distal-on-proximal segment kinematics"
and "proximal-on-distal segment kinematics"
were used in stead of open and closed kinematic chain motion, respectively (Neumann 2002, p.7).
What kind of kinematic chain
is performed as one-legged squatting?
Classification based on presence of muscle contraction
active motion：
the motion that is caused by muscle contraction
passive motion：
the motion that is created by sources other than muscle, such as from gravity
Classification based on joint kinematics
osteokinematic movement：
movements between 2 bony segments
arhtrokinematic movement：
movements between 2 articular surfaces
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Kinematic Description of Motion
Linear kinematics：
the study that is concerned with translatory motion
displacement：
the change of position that an object moves from the reference point
amplitude ¹
distance
direction
example： a person walks north for 3 m and then east for 4 m
traveling distance = 3 + 4 = 7 m
amplitude of displacement = (32 + 42)0.5 = 5 m
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velocity： the rate of change in displacement
v = dx / dt
amplitude ¹
speed
direction
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acceleration： the rate of change in velocity
a = dv / dt
amplitude
direction
deceleration： the negative acceleration
relationship between displacement, velocity, and acceleration
x = v0t + (1/2)at2
v = v0 + at
average velocity = (v0 + v) / 2
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Angular kinematics：
the study that is concerned with angular motion
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angular displacement
q = w0 + (1/2)a t2
angular velocity
w = dq / dt
= w0 + a t
angular acceleration
a = dw / dt
linear and angular conversions
q = d / r
w = v / r
a = a / r
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Example： OC > OB > OA Þ different linear displacement even though
the angular displacement is the same (= q)
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Factors That Modify Motion
Extrinsic factors
gravitation force
gravitation acceleration：
1 g = 9.81 m/s2 = 32 ft/s2
weight：
W = m×g = 9.81 m
contact forces
normal reaction force
friction force
fluid force
buoyancy
drag
lift
Intrinsic factors
friction between articular surfaces
minimized by synovial fluid
Synovial membrane is affected in patients with rheumatoid arthritis (RA).
Patients would suffer from pain when the affected joints move.
tension of antagonistic muscles, ligaments, fasciae, and capsules
Antagonistic structures are tight in patients with joint contracture.
The range of motion decreases in that joint.
anomalies of bone and joint
atmospheric pressure within the joint capsule
presence of interfering muscle bulk or adipose tissues
Help or Hinder?
Whether these modifying factors are a help or a hindrance depends on
the circumstances and the nature of motion.
Skills indicates to learn how to take advantage of these modify factors
when they influence the movement.
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