Is this post going to be snarkier than general? Quite possibly. I assume you’ve noticed that I put both words of the title in their own quotes after all.

The concept of “core strength” gets thrown about a lot in both physical therapy and exercise circles. I don’t like the usage of either term. 

I work professionally as a Physical Therapist and Strength Coach. If you are interested in my services you can contact me at: hirsch.sm@gmail.com or thru Trainerize.

What is Core anyways?

This term is one I try not to use because it’s so squishy in it’s meaning. Different people are referring to different muscles when they use this term. Or they place different degrees of importance on specific muscles. 

Usages of the term core that I have encountered and sub variations:

• The abdominal muscles: internal and external obliques, transverse and rectus
  • But with lower emphasis on the rectus
    • Or emphasis on the “lower” abdominals specifically
  • Maybe also the pelvic floor muscles
• As above but with the muscles of the low back included
  • Or with specific emphasis on the small interspinal muscles* to the exclusion of the big erector spinae
  • Of course, the latissimus dorsi are not included by most people despite the large action they have for low back stability
• Includes hip flexors i.e. the psoas
  • But only sometimes including the rectus femoris
• Includes glutes, like the medius and maybe minimus
  • But usually doesn’t include the maximus

I’m going to use the term core to collectively refer to the rectus abdominis, internal and external obliques and the transverse abdominis. These muscles ordinarily work in concert to produce everyday functional movements. I do also refer to them as the abdominal muscles.

In conversation between professionals we can just use the names of the relevant muscles. We know those words. 

When talking to clients I can see the use of the term core to indicate a vague concept. But as a professional I know I’m just using a mushy term to avoid a longer explanation for my customer.

What kind of strength are we talking about?

Because I only learned about one kind of strength in the course of my two degrees in this field. And that is maximum force production. In exercise science the meaning of strength is literally maximal F=ma. Sure you can differentiate between single muscle strength and the coordinated strength of a multi-joint movement. Or the difference between strength in a real world application versus a gym exercise. But they are all force production. 

But if we look at the exercises that are labeled as being good for core “strength” we see a lot of variation in what they are actually doing.

There are exercises like these:

Which are a dynamic version of planks, these particular variants actually mostly benefit the shoulders. 

There are exercises like these:

Which is a stability plank. It’s arbitrarily harder than a regular plank, but not in a way that requires increased force production, it’s a variation that requires increased coordination to meet the stability demand. 

Of course, I have video of myself doing these exercises because I feel that they have legitimate use for shoulder stability, which matters given my injury history and sport – historical fencing. But I don’t do them for my “core” or it’s “strength”

Other examples are isolation exercises. These include any of the various transverse abdominis isolation exercises like drawing in your belly button. But isolating a muscle contraction in a way that’s not like any real world usage is not the same thing as strength**.

Then there’s the Sahrman which is labelled as being a strength test or a “stability” test for the abs or core. But really it is just a skill test. (And I put stability in quotes because it’s not clear what’s stable here or what it has to do with any real world application)

I had an instructor straight-faced tell me that everyone starts off with a low rating on the Sahrman test, but that everyone gets better quickly. That’s a skill test then. Not a strength test. Because it takes longer than a few weeks to develop more strength. 

We did the Sahrman in class too, so I’ve tried it from the perspective of the client/patient. At the time I was deadlifting over 100% of my bodyweight with no pain. I also started low on this test and got better quickly. It demonstrably did not correlate to any real world issues in my life. 

Actual Strength = Force Production

So what does training actual strength of the abdominal muscles means? It means increasing their capacity for force production. We can do this two ways.

Fewer Muscles, Same Resistance

We can reduce the number of muscles involved but use the same resistance, usually our bodyweight. Fewer muscles with the same resistance requires more force from the muscles being used.

This is what’s going on in a one-arm plank, or a one-arm and one-leg plank.

Same Exercise, More resistance

That’s what’s going on in a weight plank.

So this is a regular plank with, in my case, 50 extra pounds, or about +25% resistance. 

It doesn’t take exercises like this to have good core strength though. I had not done this exercise in nearly two years when I shot this video. I did mostly basic exercises like bench press, deadlift and variations, squat variations, rows and pullups. If you look at the muscles used for these exercises it is clear that they use the abdominal muscles. And that they use them functionally. And that they are going to be put under high load that develops strength if you do these basic exercises at high load. (I love feeling my bench press in my hip flexors.)

I think strength of the abdominal muscles matters. Just not in the way I normally see it presented in both physical therapy and personal training. 

* There’s a debate as to whether these muscles even produce motion instead of just being positional sensors. Compare their leverage and size to the other abdominal muscles.

** Yes, of course, I am familiar with the theoretical underpinning of why TA isolation is thought to be useful, but I’m not going to explain the evidence that shows it is not, in this particular post.