Neck Strength
Aug 20 2017

Neck Strengthening and Concussions

Neck Strengthening and Concussions

Neck strengthening to reduce the risk of concussions is not a novel idea, but it is a consideration often times overlooked by medical professionals.

In light of the recent article in JAMA which examined deceased NFL players and found chronic traumatic encephalopathy (CTE) in 110 of the 111 subjects and the fact that youth football participation has dropped 25% in the last 6 years, athletes and parents of young athletes have serious concerns about concussions and their long-term effects.

Because the causes of concussions are multi-factorial, so are likely the solutions.  New initiatives are encouraging and include the advancement of protective equipment, successful training for coaches, and new policies to limit full contact practices.

Unfortunately, other initiatives may be simply bogus or, at worst, dangerous.  Therefore, it is our responsibility as medical professionals to be aware of the medical research.

Here, we’ll examine the research of neck strengthening and its potential role in concussion prevention.

G-Forces in Sports Aren’t Getting Any Smaller

A concussion occurs at about 90-100 g-force (a rolling fighter pilot experiences 5-10 g-force).  Considering that athletes aren’t getting weaker or slower any time soon and that the average high school football player takes about 652 impacts over a season, how do we best prepare athletes to handle these forces?

Numerous studies have found an inverse correlation between neck strength and peak head accelerations in contact sport athletes.  For example:

  • Gutierrez et al. looked at head acceleration in 17 female soccer athletes performing a header and found a moderate correlation between neck strength and header acceleration indicating that those with weaker necks sustained greater impacts.
  • Eckner et al. in AJSM looked at 46 male and female contact sport athletes and found that greater isometric neck strength and anticipatory activation were moderately associated with decreased peak linear and angular velocities of the head under impulsive loading.
  • Dempsey et al. examined 10 elite rugby players and found neck strength to have high correlation to lower head accelerations during rugby tackles.

It needs to be pointed out, however, that these studies had smaller sample sizes.

Fortunately, a 2014 study by Collins et al. gathered a large sample and examined 6,704 high school athletes and also found that lower levels of neck strength were associated with an increased incidence of concussion.  After adjusting for gender and sport, they concluded that neck strength is a significant predictor of concussion stating:

 

“For every one pound increase in neck strength, odds of concussion decreased by 5%”

 

Conley et al. explains that improved force attenuation can be achieved by increasing the neck muscle size; “hypertrophy in the cervical spine will allow greater absorption rates because of increased size in the cross-sectional area.”

This concept is intuitively understood by medical professionals and strength coaches alike.

However, it is difficult to make a conclusion of the beneficial effects of neck strengthening from one prospective study (Collins et al. is a level 1b evidence study).

 

Anticipatory Contact vs. Getting Blindsided

It is nearly impossible to prevent a whiplash type injury from getting blindsided.  But, anticipatory neck strength can be trainable.

Teddy didn’t even see it coming

 

A 2015 review examining the available literature on neck strength and concussion risk concluded that short-latency strength is a key modifying variable of post-impact kinematics of the head.  Meaning, that if an athlete can develop their maximum strength quicker, the athlete may better attenuate impact forces.  This is also known as rate of force development (RFD).

Because it has been demonstrated that hypertrophy and periodized training improves RFD (here, here, here), incorporating these principles into training should be a serious consideration for rehab professionals.

However, RFD is not the only variable to consider as studies (here, here) have shown that females display greater peak head acceleration than males despite initiating neck muscle activity earlier and to a higher proportion of the maximum ability. 

We need to then consider not only RFD, but peak strength and cross-sectional area as well for our athletes.

 

How Do I Appropriately Train Neck Strength?

Many strength coaches incorrectly assume that neck strength is simply achieved by compound lifts such as deadlifts, Olympic lifts, or bent-over rows.  Conley et al. found that targeted neck extension exercises improved neck muscle strength by 33.5% and neck muscle cross-sectional area by 12.8% compared to these compound lifts alone.

Similarly, many rehab professionals inappropriately select only isometric methods to develop neck strength which has been demonstrated to be not enough to develop significant increases in neck strength.

It is critical to consider that using both isometric and dynamic methods as well as isolated and heavy compound lifts are ALL important, it just depends on where the athlete is in their training progression.

There are over a dozen proposed strength training protocols in the literature.  Many of these studies demonstrate large gains in neck strength and size (Legget 1990, Conley 1997, Portero 2001, Burnett 2005, Taylor 2006, O’Leary 2007, Kramer 2013).  However, two of these studies (Mansell 2005, Lisman 2012) demonstrate that neck strengthening does not seem to reduce head acceleration.  However, the 2015 literature review notes the selected training protocols in these two studies do not appropriately dose training intensities.

Wouldn’t recommend starting with this one for your youth soccer players

Before an athlete begins a loaded isotonic neck strengthening regimen, it is recommended that they demonstrate adequate isometric tolerance and safe cervical posture with their heavy compound lifts.

Phase 1 (Isometric / Postural Training)

  • Demonstrate ability to maintain a safe cervical posture while training
    • Rows
    • Planks / Push-ups

Neck Strengthening

  • Consider starting with a training block of isometrics
    • Partner isometric holds
    • Quasi-Isometric Band Exercises

  • Adequate Deep Cervical Flexor Endurance
    • Want to ensure intrinsic stabilizers are sufficiently strong before training the primary movers
    • Mean Times
      • Men (20-40y.o): 38.4±26.2 seconds
      • Women (20-40y.o): 23.1±12.2 seconds

 

Phase 2 (Isotonic / Hypertrophy Focused / Load Capacity Training)

  • Ideally, use weights vs. bands as loads need to be progressive
  • The following recommendations are from Taylor 2006 and Conley 1997
    • 3-4x/week program for 8-12 weeks
    • Target: Cervical Flexion, Extension, Right and Left Lateral Flexion movements
    • Stay within 75% full range of motion each rep
    • Start with 1-2 warm-up sets
    • Perform 3×10 with a 10RM load
    • 2 second concentric / 2 second eccentric
    • 60-90 second rest between sets
    • When able to perform >10 reps on third set, increase the weight next session
  • Basic training devices are available such as 4-way neck machines, neck harnesses, wearable weights, and cable column attachments

 

What is ‘Good Enough’ Neck Strength?

 Unfortunately, there is no standard of measurement and analysis of neck strength to allow for systematic comparison of studies.  Therefore, clinically meaningful changes in strength cannot be determined.

The research does provide some normative data to help clinicians provide context when determining athlete readiness.

Deep Cervical Flexor Endurance Norms

  • See above

Dynamometry Cervical Strength Norms

  • Hildenbrand, 2013
    • Strength measured using a Multi-Cervical Unit
    • Examined 149 healthy male and female collegiate and high school athletes
    • Norms also provided in article
    • Below are ratios relative to extensor strength

Concussions

 

  • Florencio, et al. 2015
    • Hand-Held Dynamometry Norms
    • Examined healthy 18-55y.o. subjects (n= 31)
    • Measured in Newton
      • Cervical Flexion: 41.5 (35.7, 47.4)
      • Cervical Extension: 113.1 (102.4, 123.7)
      • Right Lateral Flexion: 72.5 (63.7, 81.2)
      • Left Lateral Flexion: 67.9 (60.8, 74.9)

 

Neck Strength Symmetry?

  • One study found reduced head acceleration during a soccer header in subjects with more symmetrical cervical flexor and extensor strength
Here’s an arbitrary standard:  1RM lift 1-Small Man/Boy Units

 

Conclusion

If properly programmed and monitored, cervical strength training has potential viability to reduce athlete concussion rates in contact sports.  Again, many variables contribute to the cause of a concussion, so always use your good clinical judgement.

 

By: Chris Hart, PT, DPT, SCS, CSCS, USAW


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