Hydraulics vs. Levers

The understanding that humans move like a lever and pulley system is a classic model. It remains the predominant way in which students are taught to appreciate motion of their patients. A long time ago anatomists discovered muscles during dissections, and they equated them to levers and pulleys, a familiar concept at the time. What they were unable to appreciate at the time, due to their technological constraints, was the water within a human being.

Ninety-nine out of every one hundred molecules in your body are water. This changes the game in terms of how we move. Water is an incompressible fluid, meaning that muscles can squeeze all they want, but water will win the battle every time. Levers and pulleys can be an effective way to move things, but hydraulics is far more efficient. Energy transfer through fluids is more complete, than in a lever/pulley system. Nature strives for efficiency.

Muscles move water around like squeezing a balloon. When you squeeze it, all the water moves away from your hand and expands into another region of the balloon. This may be a more complete representation of how we create motion. Less energy is required to produce that motion and efficiency is high.

The original anatomists propelled us forward many years ago. They helped us develop a foundation from which to think about human movement. Since then, many new laws of nature have become clear and those laws apply to everything, including us. Keeping these principles in mind, we can ask better questions and improve our thought processes leading to more optimal results.

Austin Ulrich, Physical Therapist