Levers of the Body: The Biomechanics Behind Injury Prevention and Performance
All of our joints play a pivotal role in the function of our body. They allow our various levers to function properly. When they are working pain free we don’t appreciate their complexity, but as soon as they break down we realize their purpose. To avoid the pressure we place on our joints, it benefits us to understand the 3 classes of levers and how they apply to our body. By doing so we increase our mechanical advantage which is highly influenced by the length of the active lever. Furthermore, when multiple levers are working in sync, they ultimately produce the most power. Consider the throwing of a baseball. There are 4 levers in the arm alone, with the fulcrums being the shoulder, elbow, wrist , and fingers. When you add in the slight hinge at the hips and the slight knee bend, followed by a simultaneous explosive step and the multiple actions of the arm that were just described, the power of the throw is maximized. On another note, in the sport of rock climbing we often refer to a certain type of grip as “crimping”, which is simply an act of decreasing the lever of your finger to increase mechanical advantage. If a hold is so small that you can only fit the last half inch of your finger on it, it makes more sense to completely bend the finger, driving force down through the tip, increasing the mechanical advantage, decreasing the stress on the finger, and ultimately providing a stronger more sustainable hold.
The class and length of the lever, along with the strength of the active muscle directly determines the stress on the joint. Our joints play the role of what can be referred to as the fulcrum, axis, or pivot. Throughout our body we find all classes of levers. A good example of a first class lever is a teeter-toter, aka see-saw, placing the fulcrum between the effort and load. First class levers are rare in the human body, but a good example is the atlantoociptal joint, which is the joint that connects our head to our neck. As we rotate our head in any direction it places the force of gravity directly against the opposing muscle that is working to keep our head attached to us, making that joint the fulcrum between the load (gravity) and the effort (muscle). A second class lever is easily demonstrated in the wheel barrel. Placing the load between the fulcrum and the effort. A calf raise is a good example of this in the human body. The fulcrum is the ball of the foot, while the load is in line with the leg and the effort is being applied by the calf. In a third class lever the load and effort switch, placing the effort between the fulcrum and load. An example in the human body is the hinge, the movement of lifting an object off the ground. The fulcrum is the lower back with the load going through the upper body and the force is being applied through the heels.
1st Class Lever
The fulcrum (pivot) is between the load and force (effort)
Human Example: Movement of the head with the fulcrum being the atlantoociptal joint (where the neck meets the head)
2nd Class Lever
The load is between the fulcrum and force
Example: Wheel Barrel
Human Example: Calf Raise movement with the fulcrum being the ball of the foot.
3rd Class Lever
The force is between the fulcrum and load
Human Example: Hinge (lower back is the fulcrum), Arm Raise (shoulder is the fulcrum)
Third class levers are mechanically the weakest and also the most common in the human body, so the movements that fall into that class are more susceptible to injury. This is why bending over and picking things up has caused so many back injuries. Despite the fact that the hinge is our most powerful movement, which is due to the muscle size and how many levers are working together, it also can be our most vulnerable. Our lower back becomes the target point of vulnerability in this position and without a flat back and our hips as far back as we can manage, we aren’t obtaining maximum protection of that lower back. Imagine the position of our body if we pick something up without bending the hips or knees, curved spine and all. That is worst case scenario for two reasons; a. because the load stays in the same spot while the effort shifts on top of the fulcrum, causing that third class lever to be at its weakest and b. since the spine is curved there are no muscles activated to protect the low back. Protection is built through the hinge itself, abdominal strength, along with other movements that prepare the posterior chain. By building strength and practicing correct technique, injury is mitigated. For more information on how to build proper hinge technique read both “Preventing Injury and Maximizing Strength in the Hinge Position” as well as “Proper Jumping Technique to Mitigate Lower Leg Injuries and Maximize Power”.
Our thought process when considering the value, purpose, intensity, and volume of a movement or exercise first has to be “which joint is the fulcrum and what class of lever is being used?” From there you can then decipher which muscles are providing the protection and force. Furthermore, specific movements can be applied in correlation with the purpose, with proper intensity and volume to create a steady and safe progression. Always seek the smartest way to position the body that ultimately minimizes the stress placed on it. If you are performing a movement with a long lever, an example would be a straight leg or arm, and that movement is to difficult, simply decrease the lever length by bending at the knee or elbow joint, subsequently making the movement easier. If you are searching for more difficulty, work that concept the other direction. Knowing which part of the body is playing the role of fulcrum is crucial to knowing when a movement is being performed with either bad technique, to much volume, or to much intensity. When performed correctly, the joints shouldn’t be in pain or under to much stress. By understanding this key concept, we can all be more aware of the positions we put our bodies in, ultimately promoting longevity and performance.
Nicholas S. Beauchamp, October 2019
Toyoshima S., Hoshikawa T., Miyashita M., Oguri T. (1974) Contribution of the body parts to throwing performance. In: Nelson R.C., Morehouse C.A. (eds) Biomechanics IV. International Series on Sport Sciences. Palgrave, London