a brief description of speed, velocity, axis and planes, types of pulley and its uses. this content is taken from the book the principle of exercise therapy by dena gardiner 4th edition
3. Pulley
A pulley is a wheel on an axle or shaft
enabling a taut cable or belt passing over
the wheel to move and change direction,
or transfer power between itself and a
shaft. A sheave or pulley wheel is a pulley
using an axle supported by a frame or
shell (block) to guide a cable or exert
force.
4. Types of Pulley
The following are the
types of pulley:
Fixed pulley.
Moveable Pulley.
5. Fixed Pulley
A fixed pulley has an axle
mounted in bearings
attached to a supporting
structure. A fixed pulley
changes the direction of the
force on a rope or belt that
moves along its
circumference.
6. Cont……
This is used to alter the direction of a force, and enables traction or
resistance to be applied at any angle. The pulley block is fixed to some
suitable support and the rope which passes round the wheel is
attached to the weight at one end and the effort is applied at the other.
Something analogous to the fixed pulley system is used in the body by
some muscles to allow them to be inserted at a more advantageous
angle, e.g. Digastric and Omohyoid Muscles pull round fibrous loops,
and Obturator Internus Musc‘ turns at a right angle and glides on a
ridged groove to its insertion.
7. Moveable Pulley
A movable pulley is a pulley that is
free to move up and down, and is
attached to a ceiling or other
object by two lengths of the same
rope. Examples of movable
pulleys include construction
cranes, modern elevators, and
some types of weight lifting
machines at the gym.
8. Cont…..
This device is used to gain a mechanical advantage when lifting heavy
weights. One simple combination is in common use for lifting the trunk for
Suspension exercises. The upper pulley is fixed to an overhead support, to
which one end of the rope is attached. The ropes then wound round the
movable pulley, to which the weight is attached, and round the fixed pulley,
the effort being applied at the free end.
Provided the effect of friction is omitted, the tension is the same in all parts
of the rope, therefore, if the weight (W) is 6 lbs. the tension required in each
of the two supporting ropes will be 3 lbs. and the effort (E) required will be 3
lbs. This can be expressed as:-
Mechanical Advantage =
𝑊
𝐸
=
6𝑙𝑏.
3𝑙𝑏.
= 2𝑙𝑏.
If double pulleys are used the effort required can again be reduced by half.
9. Speed
Speed is a measure of the rate of change of the
distance traveled by a moving object.
Formula:
s =
𝒅
𝒕
Where s= speed, d= distance and t= time
10. Speed in Kinesiology
Speed is defined as the ability to move the
body in one direction as fast as possible.
Agility is the ability to accelerate, decelerate,
stabilize, and quickly change directions with
proper posture.
11. Speed in Passive Movements
Speed of Relaxed Passive
Movements
The speed at which a passive
movement is performed must be
slow and uniform so that relaxation
can be maintained.
12. Speed of active movement
3 Types of speed can be followed during active exercises
1. Natural Speed
2. Reduced Speed
3. Increased Speed
13. Natural Speed
There is a natural speed for every
exercise which varies to some extent for
each individual and, in general, this is
the speed at which exercises should be
done. The effect of many exercises can
be modified, however, by an alteration in
the speed of their performance.
14. Reduced Speed
Exercises done more slowly
require greater muscular effort
and more control. Decrease in
the speed of repetitive
movements ensures time for
full-range movement.
15. Increased Speed
Rapid movement also requires strong
muscular effort but momentum is gained
and this may help to increase the range of
joint movement provided the direction is
not reversed before the free limit is
reached. Exercises performed rapidly are
stimulating but frequently lead to
inaccurate or ‘trick movements’ and full-
range movement is rarely achieved.
16. Velocity
Average velocity is the total displacement by total
time
Formula:
v = △x/△t
where ∆x is the total displacement of the body
and ∆t is the time
17. Velocity in kinesiology
Velocity is the speed of a body in a specific
direction and is the rate of change of
displacement.
Unlike speed, velocity is a vector quantity which
means it has a direction as well as a magnitude.
18. Axis
An axis is a line about which
movement takes place
Types of Axis:
1. Sagittal Axis
2. Frontal Axis
3. Vertical Axis
19. Sagittal Axis
A sagittal axis lies parallel to the
sagittal suture of the skull
i.e, In an antero-posterior direction,
as an arrow might have pierced a
yeoman in attack or in flight.
Movement about this axis is in a
frontal plane.
20. Frontal Axis
A frontal, or transverse, axis lies
parallel to the transverse suture of
the skull.
It is also horizontal and at right
angles to the sagittal axis.
Movement about a frontal axis is
in a sagittal plane.
21. Vertical Axis
A vertical axis lies parallel to
the line of gravity.
Movement about it is in a
horizontal plane.
22. Movements in Human Body
Movements of the body occur at joints, therefore axes pass through
joints and the part moved is in the plane which lies at right angles to
the axis of the movement.
Abduction and adduction (except of the thumb) and side flexion
movements take place about a sagittal axis and in a frontal plane,
flexion and extension (except of the thumb) about a frontal axis and
in a sagittal plane, and rotation occurs about a vertical axis and in a
horizontal plane.
