Figure 5-3. Types of lever systems.
5-7. SIMPLE PULLEY SYSTEM
a. In the human body when the tendon of a skeletal muscle slides over a round
bony surface, the "system" acts like a simple pulley (figure 5-4). A simple pulley
provides a change in the direction of the force or muscle pull. There is no change in the
amount of force produced by the muscle. For example, the knee acts as a simple pulley
by which the quadriceps femoris M. extends the leg.
Figure 5-4. A simple pulley (the human knee mechanism).