The Physics of the Bench Press: Science Applied

Powerlifters often tell me, “You just don’t understand physics! Don’t you know that bench pressing straight up and down is the easiest because it’s the shortest possible motion?” Well, I have to agree that some of that is correct. However, the conclusion is entirely wrong. Old dogma dies hard, so let me explain why I think this conclusion isn’t based in physics and our science in general. Don’t let the apparent technicality alarm you. We will keep it as straightforward and relevant as we can.

Explanation

Making the assumption that we want to limit our total work output in regards to completing the bench press, we will use the formula for work as our foundation: Work = force x distance

First, we have to calculate our force. Let’s use a 200-kg load as an example. The load obviously remains unchanged throughout the movement unless you have someone doing an upright row/assisted spot that you commonly see in the gym these days. For a bench press, the force is generated by the gravitational pull of the earth against the bar in your hands and is arrived at with the formula: Force = gravity x mass

For our example and use: 9.8 m/s x 200 kg = 1960 Newton’s

Now that we have the force calculated, let’s move on to the area of debate. This is in regards to the ‘distance’ the bar travels. Because the force is generated by gravity, the ‘distance’ used in the calculation is only that in the vertical plane. As you can see in the example below, a bar finishing at position A or B has the same total distance if they have the same starting position.

To say that there isn’t any force in the horizontal plane isn’t accurate. However, by doing the vector analysis, you will find these forces insignificant for calculation purposes. So we will leave them alone.

We need to think about ways we can reduce the work if we’re going to be more efficient and hopefully improve the lift. We then come to the conclusion that the only way to reduce the work with the bench press is to modify the starting position through arching, scapular retraction, and/or adding body mass. Let’s not forget that both amount to the same amount of work:

1960 Newton’s x 0.25 M = 490 Joules

So far what we’ve looked at doesn’t demonstrate a benefit to either bar path. So let us include Newton’s first law of motion: “An object in motion tends to remain in motion, and an object at rest tends to remain at rest.”

This law can easily be demonstrated if you’ve ever done pin presses versus hanging a bar suspended to the same height. If you’re allowed to swing or get the bar moving horizontally a little, it is significantly easier to press than when it is at a dead rest on the pins, even though they are at the same height (1).

Pushing the bar back right off the chest puts the bar into motion and makes it easier to begin transferring that force (1960 Newton’s in this example) into the bar. This can also help with areas of the lift where your force output is decreased due to biomechanical leverages. It also means that the force applied to the bar by the lifter doesn’t always have to be a constant and may be more or less than the needed force to complete the lift at various stages.

How does that possibly work? If moving the bar in both a horizontal and vertical plane with gravity only operating in one plane, you’re essentially using the “fourth basic machine—the inclined plane.” The formula for the inclined plane is derived in part from the same first law of motion.

Pushing the bar back and creating that longer ‘bar path’ nets the same work output. It actually reduces the required force to lift the bar through mechanical advantage. It may seem counter-intuitive, but it works. Although not entirely accurate, you can visualize it as lifting the weight with a longer lever. The force you need to apply is reduced, but you must move the lever in a longer range of motion.

A number of powerlifting groups and bench press specialists utilize techniques that take advantage of these principles. Although using a bench press shirt allows you more opportunity to take advantage of these leverages by exaggerating some of the dynamics, it still applies to raw benching as well. Even back in the 1980s, you found people analyzing the bench press groove and seeing results from these methods as noted in the following figure from an unverified research article:

Bar paths B and C represent those of Bridges and Kazmaier respectively, two elite powerlifters, while A represents a novice lifter. Kazmaier’s in particular shows the ‘inclined plane.’ These lifters lifted long before the advent of the bench shirt and utilized basic physics in the successful completion of their presses.

The intent of this article was to only take a quick look at the physics of the bench press and not be a ‘how to’ article on bench press technique. However, I will discuss a few common bench press techniques and their impacts (all letters refer to the diagram below).

  • Bending the bar toward the feet: As you bring the bar down to point D on the chest, it is even farther away from the shoulder joint than point C. However, with attempting to bend the bar and tucking the elbows to keep the elbow below the bar, you activate the lats and anterior delts. This not only provides a platform to support the weight in this position, but it also provides the power to initiate the movement back toward the face and off the chest, initiating the press.
  • Elbow tuck/elbow flare: The force is applied through the elbow. It must stay directly below the bar as you move it to the chest. This requires tucking them in toward your body, which has positive benefits as noted above and also moves the point where force is applied closer to the body. During the press, it is important to flare the elbows as the bar is pushed back to maintain the elbow position directly below the bar. If this isn’t done, an entire new set of equations come into play, with the result being the bar heading back down toward the lifters face. Elbow tuck and flare should be in direct relation to the bar position. The tuck on the way down dictates the bar position while the flare on the press is dictated by the bar position.
  • Retracting shoulders: This moves the shoulders back and moves the bar finish position slightly lower as shown in positions E to F and G to H.
  • Scapular depression (moving shoulders toward feet): By doing this, you move point H in the shoulder to point I. This helps move from point C to D and even lower if you have a good arch. This should be combined with rotation of the shoulders back out during the lift so that you can reach the same point F or this point will be behind your shoulders.

Again, the intent of this article isn’t a primer on technique. There is a lot to each of these steps, and frankly, many additional steps are needed to make it all come together successfully. If you wish to learn these, I suggest finding a coach or team that uses techniques similar to these. Bringing this all together, we end up with the figure on the left versus the figure on the right with the following force required.

200 kg x 9.8 m/s Sin(45) – 0 = 1385 N

The distance was shortened slightly reducing the work output as well.

1385 N x 0.31 M*** = 430 J

***Distance trigged out (i.e. using trigonometry) based on shoulder retraction and depression per above drawing.

If a similar technique was used on the straight line press, it would be possible to achieve the same vertical distance, which would result in a similar “work” output between the two styles. With the distance trigged out with a modified straight press (vertical) utilizing shoulder retraction and depression, you would achieve 0.22 M of movement.

1960 N x 0.22 M = 430 J

Note that although the work is the same in this straight press (vertical) using similar techniques, the force output required to press the bar is still 1960 N versus 1385 N.

Understand that these are made up examples with hand-drawn figures and estimated bar and joint locations, which I likely exaggerated in the examples. However, the important point is that even without the exaggeration, there would still be a reduction of some kind in the overall force output.

In our specific examples, we reduced our overall force output required to lift our 200-kg load by 30 percent. Here are the facts for comparison:

Straight (vertical) press example:

1960 Newton’s force required

490 Joules of work

Push back (inclined) press example:

1385 Newton’s force required (71 percent of the force of straight press in my example)

430 Joules of work (87 percent of the work in the unmodified straight press in my example)

So I began this article with a contentious claim, specifically a conclusion that I found false, and one that is commonly accepted powerlifting dogma. An application of physics demonstrates that the shortest possible motion isn’t the easiest or even the best if we are serious about bench pressing more weight.

Conclusion

This article is solely meant to address the forces applied to the bar when pressing back versus the straight press. It was only addressed in a two-dimensional plane and at the point of the bar. It becomes much more involved when looking at it in three-dimensional space and looking at the levers of both the humerus and forearm, not to mention the biomechanics such as how the humerus sits in the shoulder joint at different points of the lift. If you begin looking in depth in all these areas, you will find that they all support the similar bar path. If you wish to take advantage of these laws, I suggest you seek some one-on-one or team coaching at one of the strength training or powerlifting facilities around the world that utilize these techniques.


(1) On a practical note, next time you watch someone doing pin presses, watch the bar path, it often goes up an inch or so, and starts moving in the horizontal plane showing the natural tendency of the body to make the movement easier and more efficient. Physics explains why this is natural to do.

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About the Author

Chris Duffin is co-owner of Elite Performance Center in Portland, Oregon, and a regular contributor to Lucharilla.com. He is an elite level powerlifter totaling 2254 lbs at a body weight of 198 lbs and has competed in three different weight classes totaling over 2000 lbs in each.