Your core fires with a 57 millisecond delay – this could be why your lower back hurts

The Scenario: 45 year-old male with on-again, off-again low back pain. My physio says that my core isn’t firing properly, but I work it out almost every other day at the gym. How can this be possible?

Our core. Always seems like such an exercise buzz word. But what exactly is it?

Our abdominals are made up of essentially 4 main muscles. Anatomically, moving from superficial to deep layer by layer, we have the rectus abdominus, external oblique, internal oblique, and finally your transversus abdominus. Your rectus is the muscle that gives you the classic 6-pack, while your obliques aesthetically provide the digitations on either side. When we as physios are talking about your core though, it is the transversus abdominus that we’re referring to.

Your Abdominals

The transversus is sort of an odd muscle. It forms the deepest layer of your abdominals and it doesn’t cross a single joint, instead, wrapping around you sort of like a corset or cummerbund would.

The transverus aka your cummerbund

What makes it even odder is the way that it functions. When it comes to your core, some research suggests that it’s not really a matter of how strong it is, but rather, how good is its timing when it’s needed?

When our body performs a movement, prior to any movement actually happening, your core will contract first.1,2 It’s thought that our transversus contracts prior to any movement in order to stabilize the spine and prevent the spine from experiencing any shearing forces that may occur secondary to the movement of our limbs.

In several studies performed in 1997, it was found that in healthy individuals, the transversus contracted on average 29ms before the contraction of any muscle responsible for an arm movement, and 109ms before the contraction of any muscle responsible for a leg movement.3

From Hodges et al 1997: EMG graphs showing the contraction of the transversus (TrA) occurring before the deltoid regardless of the direction of arm movement

From Hodges et al 1997: EMG graphs showing a similar trend with leg movements – TrA would contract first before the quadriceps (RF) during hip flexion movements, TFL during hip abduction movements, and the gluteus maximus (GM) during hip extension movements

But what happens in those with lower back pain?

In 1998, Paul Hodges and company investigated the transversus contraction timing in 15 people with lower back pain (on average these people had lower back pain for 9 years, with an average of 10 episodes of lower back pain per year) and 15 people matched in age and gender with no history of lower back pain.

What they found was that the transversus contraction in those with no history of lower back pain appeared similar to previous studies – that is, it would contact prior to any muscle responsible for limb movement.

But in those with lower back pain – the contraction of the transversus came on average 57 – 86ms after the leg movement had already occurred.

From Hodges et al 1998: note how the contraction of the transversus (TrA) occurs after the contraction of the lower leg muscles

But a question arose from these results – the proverbial chicken-or-the-egg – was it pain that changed the timing of the core or was there always a timing issue that made these people more likely to experience shearing forces and consequently low back pain?

So in 2003, Paul and his research team set out to investigate.4 In this study they took 7 healthy volunteers with no history of lower back pain. EMG of the core was measured the same way as in all other previous studies conducted by this group, and as with previous studies, transversus contraction seemed to precede that of all other muscle groups. And then pain was experimentally introduced. Pain was introduced via injection of a noxious stimulant (hypertonic saline) at the level of L4 to produce a pain intensity of at least 4/10 (where 0 is no pain and 10 is the worst imaginable). When a pain stimulus was present, the transversus contraction appeared to come on progressively delayed.

From Hodges et al 2003: a terrific transversus contraction pre-pain injection; note the delay post-pain injection

Great research that helps lend some support that pain changes the way that we move. And also great research to show that even when things are working completely fine – the introduction of pain, even within the same day, can change things.

Based off this research I always tell my guys that even if your core was working perfectly fine and you’ve been hitting the gym and going through your core routine consistently, the second that you experience low back pain, there is a likelihood that things could have changed.

Is it all about the strength? Or is it all about the timing? The truth is, it’s probably both. But the real takeaway is that pain will change how your core works even if it was working great before. So even if you've been killing it at the gym, re-set and re-start, cause it'll make a difference.

References:

1. Hodges PW, Richardson CA. “Feed-forward contraction of transversus abdominis is not influenced by the direction of arm movement.” Experimental Brain Research 1997;114:362-370.

2. Hodges PW, Richardson CA. “Contraction of the abdominal muscles associated with movement of the lower limb.” Physical Therapy 1997;77:132-144.

3. Hodges PW, Richardson CA. “Delayed postural contraction of the transversus abdominis in low back pain associated with movement of the lower limb.” Journal of Spinal Disorders 1998;11(1):46-56.

4. Hodges PW, Moseley GL, Gabrielsson A, Gandevia SC. “Experimental muscle pain changes feedforward postural responses of the trunk muscles.” Experimental Brain Research 2003;151:262-271.