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Moment Arms and Why You Should Care

March 14, 2019

Moment arms aren’t necessarily something the average lifter thinks about, but it’s really important to have a basic understanding of how forces are acting on your joints.

  1. It’s critical in terms of injury prevention

  2. It helps you maximize the amount of weight you’re able to lift

In simple terms, a moment arm is the length between a joint axis and the line of force acting on that joint. Every joint that is involved in an exercise has a moment arm. The longer the moment arm, the greater the load applied to the joint axis.

Let’s start with high-bar back squat vs low-bar back squat. 

As you can see from the length of the red lines, high-bar squats are a much more knee-dominate movement, while low-bar back squats are more hip-dominant.

Why this matters:

Generally speaking, if you’re back squatting for general fitness (not competitively) and have had a history of back pain, you might do better with high bar squats. If your knees are problematic, low-bar back squats might be a better option. (Having said that, this is just one of many factors that come into play when determining which method is best for any given lifter.)

Now let’s switch gears and look at moment arms when bench pressing. 

Most experts recommend an arm angle somewhere between 45-65 degrees. If you have a fairly narrow grip (an arm angle closer to 45 degrees), you’ll end up with a much longer moment arm, and the stress on the shoulder joint will be greater. )Want to know more about bench press mechanics? Check out this article).

Why this matters:

One isn't necessarily better than the other, but shoulder health is something to consider when deciding hand placement/arm angle.

One last look at bench press - let’s talk wrists. 

A neutral wrist means there’s little to no moment arm at the wrist joint. 

Why this matters:

Laying the hand back and letting the bar roll toward the fingers puts a great deal of unnecessary stress on the wrist. The wrist is a small joint - it won’t tolerate a heavy load for long!

Okay. So now you know. No excuses. Before you get under the bar again, take a minute or two to think about moment arms. We want you to stay safe while maximizing your efforts!

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