Can neck strength reduce the risk of concussions in sport?

A question that has come up recently in the world of concussions has been which neck strengthening exercises are the best for reducing the risk of concussion?  The answer to which, unfortunately, is not so simple.  A better question to ask is does neck strength actually have the ability to reduce the risk of concussions?

 

The answer to the second question is two-fold and requires further information about the nature of the impact as well as the state of the person on the receiving end of this impact.

 

Concussions are a result of the ACCELERATION and/or DECELERATION of brain tissue within the skull.  If a person is stationary, a direct blow to the head or body will most likely result in a certain acceleration of the head and therefore the brain.  If a person is moving and suddenly met with an abrupt stop from a wall or 300-pound linebacker, the brain continues to travel inside the skull that has been abruptly stopped.  This results in a quick deceleration of the brain tissue within the skull.  In either account, the result is an accelerative or decelerative impulse delivered to brain tissue.

 

Most cranial accelerations/decelerations in sport have been found to be around 18 to 23 g’s (where g equals the force of gravity).  In fact extensive studies on impacts seen in college and high school football found that more than 70% of impacts were below the 30 g mark.  These same studies also found that the threshold acceleration for a concussion injury was within the range of 70 to 120 g’s.  This is why not all hits to the head result in a concussion; the acceleration is simply not high enough.  On the other hand, a hit does not have to be delivered directly to the head to cause a concussion.  A hit to the body, or even a minor fall, can also lead to a concussion provided that the incident results in a significant translation of acceleration to the head.

 

In 2007, a researcher by the name of Viano and his colleagues examined impacts seen in professional football.  They then modeled these impacts and played with the variables in an attempt to determine how the acceleration of one’s head can be decreased during and after impact.  If we can decrease the acceleration of the head, we reduce the risk that the impact will cause a concussion.  After examining all of the variables (i.e., helmet padding, etc.) it was determined that the variable with the greatest influence on head acceleration was NECK STIFFNESS.  Increasing neck stiffness effectively couples the head with the torso meaning that with a rigid neck, in order to move the head the whole torso would have to move as well.  This effectively increases the moment arm and drastically reduces the acceleration of the head.

 

So…

Neck Stiffness = ________1_____________

                               Head acceleration

 

Or…

↑ neck stiffness = ↓ head acceleration = ↓ concussion risk

The results of this study hold consistent with a very early animal study done in the 1940’s.  There were 2 conditions in this study. Group 1 received an impact to the head that resulted in a concussion injury.  Group 2 received an impact of the exact same magnitude however this group had their heads and necks fixated in place so that there was no movement of the head following the impact.  If there is no movement of the head, then no acceleration of the head takes place, and thus these animals did not suffer concussions even though they were impacted with exactly the same force.  It again appears that neck stiffness can prevent concussion injuries.

 

This has falsely prompted many individuals to promote neck-strengthening programs to reduce the risk of concussions.  There is one major problem with this theory however…

 

NECK STIFFNESS is NOT the same thing as NECK STRENGTH

Neck stiffness REQUIRES neck strength (or a rigid brace), however neck strength does not translate into neck stiffness.  You can have the strongest neck in the world, able to lift 10 cars with a single chin tuck, however this is only when all the muscles are actively firing.  When the muscles are relaxed, the neck is serving its other purpose: to be an extremely mobile structure allowing for rotation of the head and scanning of your environment.

 

As stated above, the answer to our question is two-fold and requires further information about the nature of the impact.  The information required is: did this person know they were going to be impacted or not?

 

If a person is aware that they are going to be impacted (with sufficient warning), they are likely to tense up their body and contract their neck muscles in a subconscious attempt to link their head with their torso and decrease the resultant acceleration of their head.  So if the person knows that the impact is coming, a STRONGER neck can actually become a STIFFER neck and therefore reduce peak head acceleration and therefore concussion risk.  Those with weaker necks would theoretically not be able to create sufficient tension and therefore may be more at risk for suffering a concussion.

 

But, how about those who are unaware that the hit is coming?

 

Most concussion injuries happen when the person is unaware that they are about to be hit and there is an extremely logical explanation for this considering the information we have just provided for you above.  The person does not have their muscles contracted at all times when on the playing field and most of the time they are actually using their neck for it’s mobility function to remain aware of the play around them.  Think of the receiver getting hit just after receiving a pass over their outside shoulder, or the hockey player moving quickly up-ice through the neutral zone only to receive the dreaded ‘suicide pass’.

 

“Keep your head on a swivel” as my coach always used to say.

 

The problem is that keeping our ‘heads on swivels’ reduces our neck stiffness and therefore increases our risk for concussions to happen.  Peak acceleration of the head has been shown to occur within the first six to twenty milliseconds (6-20 ms) during impact.  Studies surrounding whiplash have demonstrated that it takes roughly 100 to 200 milliseconds to even start to contract the muscles in your neck and another 150 or so milliseconds to even reach one half (1/2) of the maximal contractile ability of those muscles.  So in effect, if someone is unaware that the impact is coming, the concussion has already occurred before they can even think of contracting the muscles of that big strong neck they’ve been working on.

 

A 2011 study lead by some of the biggest names in concussion research (Jason Mihalik, Kevin Guskiewicz, and Robert Cantu) actually tested the theory of neck strength having a protective effect against concussions.  They tested a bunch of 16-year-old hockey players before the season on their neck strength in a number of different directions.  The helmets of these players were instrumented with accelerometers to look at the resultant head accelerations from impacts received throughout the season.  The results demonstrated that there were no differences across the different groups of neck strength in any of the planes.  This means that even those with the strongest necks experienced the same level of cranial accelerations as those with the weaker necks.

The conclusion of this particular study reads as follows:

 

“Our hypothesis that players with greater static neck strength would experience lower resultant head accelerations was not supported.  This contradicts the notion that cervical muscle strength mitigates head impact acceleration.”

Mihalik et al., 2011

 

Once again, neck strength does not equal neck stiffness.  In order for a strong neck to be stiff, you have to be contracting your muscles actively.  Put another way, you could have the strongest neck in the world but unless you have contracted your muscles fully, this strength does not translate into stiffness..

 

To summarize, does neck strength have the ability to reduce the risk of concussions?  As stated above, the answer to that question is two-fold:

 

If the person is aware that the impact is coming, and has atleast 300-400 ms before impact to brace, then having a stronger neck will protect them from suffering a concussion injury.

 

If a person is unaware that the impact is coming (majority of concussions), they will not have their neck muscles contracted and therefore having a strong neck is of no use to them and they are more likely to suffer a concussion.  This is of course provided that the impact delivers the required acceleration to the brain tissue.

 

If you have any questions or comments, or you’d like to pose your own concussion question, please feel free to send them to info@completeconcussions.com and our researchers will answer them for you!

2 replies
  1. cian
    cian says:

    Makes a lot of sense. Its always the one you don’t see coming that gets you. No time for your body to tense and be ready for it before the impact.

    Reply

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