joint mechanics

Biomechanics 101: Understanding Lever Classifications

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Biomechanics 101: Understanding Lever Classifications

If biomechanics were understood as comprehensively as is used by lackluster sports and health professionals trying to demonstrate their competence and knowledge, the world would be floating atop some Matrix / Vitruvian Man mash-up. To implement any of the core tenants of biomechanics at even a modest level, where its implications actually have some semblance of an influence on performance programming design, one must first understand the most rudimentary elements of mechanics.

Some of this may be intuitive, some may not, but regardless, understanding lever classifications will bring the machinery underpinning the human body to the forefront of consciousness next time you are exercising or designing a training program.

This concept is going to get another step simpler as we begin to look at the four primary elements of any lever system. The four elements are: load, fulcrum, effort, and lever arm. As it relates to human kinetics, load can be thought of as some segment of the body that you are trying to move, a weighted barbell, or an object like a baseball or soccer ball. The fulcrum is the point at which any pivot or movement occurs as the effort is applied to move the load. The lever arm is the object on which all of these forces are acting. The traditional example of this is a seesaw like you would find in a playground. The center of the seesaw is the fulcrum, while the load and the effort continue to alternate as the opposing individual hoists themself against the resistance of their opposing counterpart; this however, is just one example of the organization of these elements. As you’ll soon see, where the fulcrum, load, and effort lie in relationship to one another is how we classify levers.

Class 1

In Class 1 Levers, the fulcrum sits in between the two opposing forces of the load and effort. Although this classification doesn’t occur with much frequency in the human body, it is one of the easiest to understand. Consider the above seesaw, this is a Class 1 Lever in its purest form. One of the few examples of this in the body is the atlanto-occipital joint. Nodding the head forwards and backwards displays this as the force input and outputs reverse as you nod forwards vs backwards (over the fulcrum of the aforementioned AO joint.

Let’s make this matter more confusing before you get too comfortable with this idea… Superficially it may seem as though lever classifications in the body are black-and-white, much grey* does indeed exist. Consider this example of an overhead triceps extension: when pictured this seems like a clear case of Class 1. We have the triceps inputting force proximal to the elbow, with the elbow clearly acting as a fulcrum, while distally, we have the output force or load (cable or dumbbell) being acted upon. Upon closer examination, the precise insertion point of the triceps insertion on the Olecranon process (the elbow) seems to indicate that this may not be such a clear delineation as the input force is also the fulcrum.

But this is a 101 level intro so let’s not get carried away in graduate-level theory…

Class 2

Lever classification isn’t all that interesting, but I think Class 2 is as interesting as it gets. In Class 2, the input and output forces are next to each other, while the fulcrum exists at the end of the system furthest away from the effort. The simplistic go-to example here is a standard calf raise; though simple the implications of this are tremendous…

Since the load and effort are next to each other, the mechanical advantage amplifies output capacity. This brings to light yet another term to define. Mechanical advantage—yet another word synonymous with “I’m smart and know what I’m talking about” in gym speak. Mechanical advantage is used to express the difference between the force input and what its potential output can be based on the totality of the variables within the system.

Mechanical advantage is what provides an athlete with long arms his ability to pitch on the field or take long, powerful strokes in the pool, while limiting his ability to bench press or do most traditional weighted exercises (deadlift not withstanding).

Another example of this is a very common exercise amongst our programs, the landmine overhead press. Consider the load (weight on the bar) as it sits between the working hand (effort) and the fulcrum (the landmine attachment itself).

This is also what has provided the mammalian ankle structure with its clear benefits on an evolutionary timeline. Class 2 provides significant output with minimal force input, allowing for energy conservation yet consistent output over extended distances in the form of locomotion.

Class 3

Just like in Class 2, the fulcrum exists at the end of the system, but now the input and outputs are reversed. Now, the load sits next to the effort, but opposite the fulcrum. This provides the tremendous force inputs necessary for things like mastication (chewing) or slamming the sledgehammer against a tire.

The inefficiency of this system is both a feature and a flaw. In the case of the sledgehammer, it can do serious damage during demolition projects, but at the expense of a great deal of energy. This is why sledgehammer work is so taxing during workouts. 

Class 3 is partially responsible for the large range of biceps curl strength (even in untrained individuals). As a result of genetic variation, the insertion of the biceps can be millimeters closer or further from the elbow. As this force input migrates closer to the load from one individual to the next, less force is required to lift the same output. Consider trying to do a chest-supported row with your hands almost touching the base of the machine vs. out closer to the weight.

Understanding Biomechanics

As you begin to understand this more fully, it will help you interface more successfully with challenges and conventional wisdom in your sport or domain. Next time you’re in the gym, consider the exercise you’re doing and how it relates to these lever classifications.

*Grey can be spelled as such or g-r-a-y. This spelling seems
suspicious to me and anyone who uses this should be under constant
state-sponsored supervision.