Sports Biomechanics is a pretty big field so I’ll make no attempt to even summarize what it is in this small post. Instead, as I try to do always, I’ll zero in on something small enough to blog about and attempt to touch on just enough detail to maybe spark some further interest on your part. The small portion that I’ve chosen here is the topic of levers. Why? Well, because for the average Joe in the gym this is probably the simplest and most applicable concept that I can think of. It ain’t gonna change how you lift, well I don’t think it will anyway, but it may help you better understand some of the positions you find yourself in and why some things are harder or easier this way or that way.

So let’s start with defining a mechanical lever. A picture here is worth 1000 words; it’s basically the rod that is placed over a fulcrum. A load is placed somewhere on the lever and a force is applied somewhere else on the lever.  Like this:

Not too difficult to understand right? OK, so now lets define a few different types of levers.  A type, or class, of lever is defined based on the relative positions of the force, the fulcrum and the load. One more term to define, “moment arm”.The moment arm is the perpendicular distance between the line of action of the force to the fulcrum (don’t worry, upcoming pictures will clear it up.) Here’s a description of the lever classes:

• First Class Lever: When the force and the load are on opposite sides of the fulcrum (like in the picture above.)
• Second Class Lever: When the force and the load are on same side of the fulcrum and the moment arm of the force is longer than that of the load.
• Third Class Lever: When the force and the load are on same side of the fulcrum and the moment arm of the force is shorter than that of the load.

So how we we apply these fundamental definitions to the gym? Well, there’s all sorts of applications and I’ll borrow a few pictures from The Essentials of Strength and Conditioning to demonstrate.

A first class lever applied to a triceps extension is shown here. See how the muscle is pulling to the left forcing the forearm to the right working against the resistance force going left? If you look hard you can see the moment arms that I described above. There is one for the force and one for the resistance (aka load). Hopefully you can see how each is the perpendicular distance from the fulcrum or the elbow in this case.

One more term to define and that’s mechanical advantage which is simply the moment arm of the force divided by the moment arm of the resistance. Basically a moment arm of less than 1 is a disadvantage, it makes moving the load more difficult. A moment arm that is greater than 1 makes it easier. Take another look at the picture above of the 3 dudes trying to use a tree trunk, or whatever that is, to move the boulder. Which one you think is in the most efficient position? If you figured out that the guy all the way to the right is best positioned because his moment arm (force) is largest thus his mechanical advantage is largest then you’re right!

OK so now lets look at a second class lever – a calf raise. See how both the force and the resistance are on the same side of the fulcrum? The fulcrum here is the ball of the foot if that’s not obvious. Also this picture again shows the moment arms as the perpendicular distance from the force to the fulcrum. So you might be asking how can this knowledge actually be applied… we’re getting there.

Finally an example of a third class level – a biceps curl. As with the second class lever you can see how the force and the load are on the same side of the fulcrum which in this case is the elbow. See how in this case the moment arm for the force is super small compared to the moment arm for the resistance? That’s what makes this third class versus second class like a calf raise.

So how do you use this at the gym? Well, as I said earlier I doubt this will change how you lift but think about your form knowing a little more about the mechanics. Take standing bicep curl for example. If you are not keeping your arms in a fixed position (upper arm perpendicular to the floor) during the entire movement then you are cheating your muscles. How? Well look at the picture above but imagine the elbow is further back to the left. What does that do to the moment arm for the resistance? That’s right, it makes it longer which increases the mechanical advantage which means you’re doing less work to move the weight. I’ll leave it to you to think about the other examples and how common cheating techniques can be easily understood with just a small amount of biomechanics and mathematics 🙂