It is also called moment arm in some textbooks.
Lever arm is always less than or equal to radius.
In the previous example, the force is applied at a 70 o angle to the stick. Lay a straightedge on this line, then rotate the straightedge 90 o . Using the example above, the lever arm is formed by extending the line of the pulling force to the left, then drawing the red perpendicular line segment shown in this figure. The muscle must exert a huge force because of its small leverage, in order to produce a torque on the arm.