The Physics of Benchpressing

The Physics of Benchpressing

May 5, 2013

By: Devan Doan

First of all, I need to give all the credit of this article to my Dad, Dave Doan. When I first started lifting and he was trying to convince me that maxing out every day wasn’t going to make me stronger, he used this to explain the importance of technique. Two of our biggest focuses is speed and decreasing distance of bar travel (arching, wider grip, etc.). My Dad is an engineer, so by trade he’s very logical and a little bit nerdy! 🙂 So bear with me as you read this. It really does have some good info.

The following are a few general laws of physics:

Power = Work / Time
Work = Force x Distance
Speed = Distance/ Time

Therefore:
Power = Force x Distance / Time

Since the words force and strength are commonly used interchangeably we can more simply define Power as strength multiplied by speed.

Strength x Speed = Power

Since strength and speed are both components of power, increasing one of them and not increasing the other limits total power. To better explain this, assume that an arbitrary strength score for an athlete is 2, and the athletes arbitrary speed score is also 2. The hypothetical power rating would be:

2 x 2 = 4

Doubling strength without improving speed would double the power:

4 x 2 = 8

If the same athlete made only a 50 percent gain in strength and an equal gain in speed, the power rating would be:

3 x 3 = 9

Seeing this, it becomes very clear that not only must one increase strength, but also increasing speed will make you more powerful.

Distance of Bar Travel:

Take a look at the equation:

Work = Force x Distance

Simply stated if we apply a constant force to the bar, the farther the bar moves the more work it takes to complete the lift. By shortening the distance the bar travels and applying the same force, we can complete the lift with less work. Since work is a factor of power:

Power = Work / Time

The amount of power to move the bar from chest to lockout is reduced.

 

Alright, it’s ok if you have to read this a few times over before it all soaks in. I still have to read it a couple times! 🙂 And you thought you’d never use physics again…. 🙂

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