The document discusses levers in the human body. It defines a lever as a rigid bar that moves around a fixed fulcrum with two forces applied. The three main parts of a lever are the fulcrum, resistance/load, and effort. The document describes the three classes of levers - first, second, and third - based on the relative positions of the fulcrum, resistance, and effort. It notes that the second-order lever, where effort lies between the fulcrum and resistance, is the most frequent type seen in the human body.

1. Lever system in human body
Suparna Bandyopadhyay
MPT Neurology

2. Definition:
The lever is a rigid bar that moves around a fixed fulcrum
with two forces applied to it.

3. ▪ Fulcrum:
It is a fixed pivot point.
The fulcrum lies in the joint of the human body
 Resistance: The weight or load that has to be moved
Internal resistance: Body weight
External resistance: Gravitational force
 Effort: The source of energy that will do the work
In the human body effort point lies in the insertional point of muscles

4. Fulcrum
Load
Effort

5. Effort arm : Distance between the effort and the fulcrum.
Resistance arm : Distance between the Load and the fulcrum

6. First class lever – the fulcrum is in the middle of the effort and the
load.
Second class lever – the load is in between the fulcrum and the
effort.
Third class lever – the effort is between the fulcrum and the load.

8.  Resistance and effort are equidistant from the fulcrum
 The effort is closer to the fulcrum than the load, the lever provides
no mechanical advantage but increases the speed with which the
load can move
 The distance from the effort to the fulcrum is long and the distance
from the load to the fulcrum is short. A small effort can move a large
load
 Lever of “equilibrium and stability”

9. Resistance Effort
Resistance Effort
M.A=1
M.A
less
than 1
M.A
more
than 1

11. A second-order lever is a machine with the effort and resistance on the same
side of the fulcrum, with the effort force furthest from the fulcrum.
 Lever of “power”
 The mechanical advantage is always more than 1 as the effort arm is
longer than the load arm

13. A second-order lever is a machine where the effort lies between the
fulcrum and resistance
 The effort arm is always smaller than the resistance arm, mechanical
advantage is always less than 1
 The most frequent type of lever present in the human body
 Lever of “speed”

15. 1st order lever
Lever of stability
2nd order lever
Lever of power Lever of speed
3rd order lever
Most common type of lever seen in the human
body?