Touching on a fitness-anatomy related topic, because knowing how your body works is essential pretty much like knowing how your latest gizmo or the massive V8 inside your car’s hood (if you own one 😉 ).
The human body is a complex system of levers that enables us to perform everything from very basic to extremely
complex movements. Individually, levers are simple machines, and we can think of the body as a collection of machines.
Bones are the rigid frame part of the lever machine through which force is transferred.
A lever is a bar that turns on an unmoving point called a fulcrum. When you push or pull on one end of
the bar that pressure is called the force. The object that is lifted on the other end is called the load.
There are three parts to all levers:
• Fulcrum – the point at which the lever rotates.
• Applied Force (also called the effort) – the force applied to the lever.
• Resistance Force (also called the load) – the force applied by the lever to move the load.
First-Class Levers- With a first-class lever, the axis or fulcrum always lies between the force and resistance (F-A-R). A first-class lever
can perform all four basic machine functions: (1) balance forces, (2) change direction of the force applied, (3) modify
(increase amplify) the force applied, and (4) modify the speed and or range of motion.
This is a good point to introduce the concept of mechanical advantage. Think of a teeter-totter, exactly 10 feet long
end-to-end, with the fulcrum at dead center and a 50-lb. kid on each end. What will happen if they just sit there?
Right. Nothing. The forces are balanced, and without a little leg push from one of the kids no one goes up or
down. Now think about when you were a kid and how hard you had to push to go up. Not very hard. That’s the
lever system giving you a little advantage.
Second-Class Levers –
With a second-class lever, the resistance is in the middle, between the axis and fulcrum (F-R-A). The most easily
identified example of this class of lever is the wheelbarrow. In this arrangement the force arm is always longer than the resistance arm, and this favors force production. In an unweighted human producing unresisted
joint movement in the lab, this is true. However, in sport and exercise we can find several examples of the body as
a whole acting as a second-class lever. An easy example is the push-up.
The third-class lever is the most common type of lever in the human body. With this class of lever, the force applied
is in the middle, between the resistance and the axis of rotation (R-F-A). In this lever arrangement, the resistance
arm is always longer than the force arm. The easiest and most recognizable such lever in the human body may
be the biceps and elbow. Think of the resistance being in the hand and the elbow as the axis. The force applied to flex the elbow, although produced in the upper arm, is applied to the system between the elbow and hand.
Anatomically we are dealt a fairly static hand when it comes to levers: we are built the way we are. We can’t train
to change the location where muscles attach to bones in order to improve mechanical advantage, but we can teach
(1) better performance leading to faster fitness gains and (2) safer exercise sessions. Accomplish these two
things and we all win.