Neck Strength and Concussions, Assisted vs Resisted Training

Reading Time: 7 mins

As we learn more about head injuries, we continue to seek new ways to protect our athletes. Sport officials have proposed rule changes, equipment modifications, and other ideas that have been speculated to help mitigate the risk of concussions. Instead, this article investigates neck strength as a protective factor for reducing the risk of concussion in high school athletes.

“In the US, concussions are a common sports injury, with an estimated 300,000 recognized and 7–9 times that number of unrecognized sports-related concussions annually.”

“To date, primary prevention has focused on three areas: (1) improving helmet designs, (2) considering introducing helmets to sports not currently utilizing them, and (3) adopting sport rule changes.” So now we ask what about training interventions? Helments help protect against blunt trauma but are “…ineffective at preventing rotational accelerations, the primary underlying mechanism of concussions.”

Poor neck strength has been speculated to increase the risk of concussion. This paper serves to:

  1. Develop and validate a cost effective tool to measure neck strength in a high school setting
  2. Conduct a feasibility study to determine if the developed tool could be reliably applied in a high school setting by certified athletic trainers (ATs)
  3. Conduct a pilot study to determine if anthropometric measurements captured by ATs in a high school setting can predict concussion risk

Methods:

In order to test the validity and reliability of the proposed testing method, 16 adults were repeatedly used for anthropometrical testing by five different athletic trainers. Each of the five athletic trainers ranged in experience from very inexperienced to more than 20 years’ experience. Each of the subjects undergone two different isometric neck strength tests using a tension scale held by an athletic trainer. The varying experience between AT’s serves test levels of inter-tester reliability.

Nation-wide, participating high school AT’s captured “…head and neck circumference, neck length, and four measurements of neck strength (i.e., extension, flexion, and right and left lateral) for all athletes participating in school-sponsored boys’ and girls’ soccer, basketball, and lacrosse using a cloth measurement tape and the tension scale apparatus developed for this study.” This information was compiled electronically and the students whom participated were monitored for concussions over the course of the next year.

“The new apparatus developed for this study, a hand-held tension scale attached to a Velcro adjustable head strap with a D ring, measured neck strength (in pounds) in a similar manner but with the device located on the opposite side of the head and the athlete instructed to apply maximum force by pulling against the tension scale for 3 s (Fig. 1).” This device costs approximately $10 whereas the traditional handheld dynamometers can cost $750-$1,000 each.

“Of the 176 schools participating in the 2010 High School RIOTM study, 32 participated in this pilot study, and of the 174 schools participating in the 2011 study, 40 participated. Of these, 21 schools participated both years. Thus, a total of 51 schools from across the US participated. ATs, who are medically trained professionals, reported pre-season anthropometric measurements for 6,704 high school athletes in boys’ and girls’ soccer, basketball, and lacrosse and then reported concussion incidence and athletic exposure data during the course of each sports season via the High School RIOTM system.”

Results:

The pilot study found a high correlation (0.83 to 0.94, p < 0.05) between the handheld dynamometer and tension scale measurements for neck strength. Thus, either tool would be appropriate for testing neck strength.

The tension scale feasibility study showed high levels of inter-tester reliability. 75% of the testers were correlated above the 0.80 level (p < 0.05).

All four neck measurements (flexion, extension, right/left lateral flexion) did seem to show high correlation to the predictability of concussion for males (0.87-0.97) and females (0.89-0.97).

A total of 179 of the measured 6,662 athletes had diagnosed concussions, with females (4.9 per 10,000) having an incidence almost twice as high as males (2.5 per 10,000). “Soccer had the highest rate of concussion (5.2) followed by lacrosse (3.7) and basketball (2.3).”

“Concussed athletes had a smaller mean neck circumference (p = 0.001), smaller mean neck circumference to head circumference ratio (i.e., a small neck paired with a large head; p = 0.001), and smaller mean overall neck strength (p < 0.001) than uninjured athletes.”

“Overall, neck strength (p < 0.001), gender (p < 0.001), and sport (p = 0.007) were all significant predictors of concussion in unadjusted, univariate models.”

Discussion:

Testing neck strength with tension scales may be a simple and reliable method for athletic trainers in the high school setting. With this information, we understand that poor 4-way neck strength is likely to expose a high school athlete to increased risk of concussion.

It was also observed that neck girth may also be a protective function. This may explain why females were recorded to have higher incidences than males in this particular study; at least for soccer, basketball, and lacrosse.

“Even a small decrease in velocity may result in a significant reduction in the risk of concussion (Viano et al., 2007).”

The NSCA has a Point/Counterpoint Column that is brief and very applicable. The February 2018 column, edited by Andy Galpin, was titled Assisted Versus Resisted Training: Which Is Better for Increasing Jumping and Sprinting? Below are few focal points for each training method.

Point: Assisted Training by James J. Tufano, PhD, CSCS*D

  • The force-velocity curve is often trained in an unbalanced manor from resistance training alone, due to overload rather than overspeed. Therefore, power is only enhanced by way of force development, not velocity . When comparing the power and force equations, the crucial difference is that power shows a respect for velocity- quite possibly showing the necessity of overspeed training.
  • The principle of specificity says “…if an athlete trains at a specific speed, performance is likely to improve at and around that speed.” This is often achieved by towed running or assisted jumps.
  • “Specifically, towed or assisted sprint training “pulls” the athlete forward, facilitating an increased stride length, stride frequency, or both to achieve a supramaximal velocity.”…“Similarly, assisted jumping “pulls” the athlete upward, reduces bodyweight, and allows for greater takeoff velocity and, consequently, jump height.”
  • Postactivation potentiation has demonstrated acute performance enhancements. “For example, assisted jumping with 30% bodyweight reduction has been shown to potentiate subsequent bodyweight takeoff velocity by approximately 7%.” Previous literature showed the same assistance had “…resulted in bodyweight vertical jump height increases of 7.8–8.6% in active university students, 6.5% in professional rugby players, and 11% in highly trained volleyball players…”
  • “One study showed that bungee-assisted sprinting (30% bodyweight reduction) acutely results in faster sprint times over short distances up to 15 m compared with normal sprinting.” Repeated exposure to overspeed training also showed lasting benefits. “ For example, downhill sprint training for 6 weeks has resulted in greater increases in sprinting speed compared with flat or uphill sprint training as long as the decline slope is not steep enough to result in increased breaking forces during foot strike. Another study showed that 4 weeks of assisted sprinting using a commercially available bungee device (approximately 15% bodyweight reduction) resulted in greater improvements in acceleration up to 15 yards and mean velocity during 40-yard sprints compared with traditional and resisted sprints.”
  • “Therefore, it is important that the strength and conditioning professional use assisted and resisted training across a variety of loads.”

Counterpoint: Resisted Training by William E. Amonette, PhD, CSCS

  • “Although stride rate is largely dependent on neural factors and motor learning, stride length is determined by the magnitude of the ground reaction force (GRF) with each foot strike. As such, maximum sprinting speed is largely reliant on force and rate of force development.”
  • Considering the same concept with jumping, “…height is predominately affected by the magnitude of the GRF and the resultant velocity of the center of mass (i.e., power) at takeoff.” Plain and simple, GRF’s are key. Increases in skeletal muscle mass from resistance training in known to improve strength, and therefore force production which results in greater GRF’s.
  • “Some have postulated that training near the load that maximizes peak mechanical power output in a lift, which typically occurs around 30% of peak isometric force production or 40–60% of the 1RM, may be most beneficial for improving speed. Others theorize, based on the size principle of motor unit recruitment, that heavier loads with high intentional velocities could be better for improving power.” It is more likely that periods at various loads/velocities will provide the greatest enhancement of power.
  • When performing a heavy resistance exercise (such as back squats at 85% of 1RM) before a jumping movement, subsequent peak GRF and jump height are both increased. This enhanced neuromuscular response subsequent to heavy squats has also been shown by others who demonstrate a postactivation potentiation response from heavy-loaded squats followed by jump squats at a range of loads (6).” Similarly, heavy back squats allowed decreased 10m, 20m, and 30m sprint times, when lifting at high intentional velocities.
  •  “Harris et al. studied 18 elite rugby players, who were randomly assigned to train with a heavy load (80% 1RM) or individualized loads that maximized mechanical power output (between 20% and 40% 1RM). After a 4-week familiarization period and a 7-week training period, “…data indicated significant decreases in sprint time within both groups, but no significant differences between groups.”In agreement that various loads are effective, McBride et al. found similar results when studying heavy (80% 1RM) versus light (30% 1RM) squat jumps in athletic men. Significant improvements in loaded jump kinetics and performance were observed in both groups across an array of loads.” Likewise, another paper demonstrated “…research showing trained men using combined loads of 30% of their peak isometric force production and 80–85% of their 1RM concurrently in a training plan experience improvements in jump power, jump performance, and 10-m sprint time.”
  • “In a large sample of 64 weight-trained subjects, Wilson et al. compared the effects of training with bodyweight plyometric exercises, heavy resistance exercise, and resistance exercise using individualized loads that maximized mechanical power output. After 10 weeks, “…It was determined that the maximal power training increased jump height at midstudy and poststudy. The bodyweight plyometric and heavy resistance training groups experienced significant increases poststudy, but not at the midstudy testing point.”
  •  “In conclusion, resistive jump training performed with heavy loads results in an acute neuromuscular potentiation response and a subsequent increase in jump and sprint performance.”

 

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Thanks, 
AJ

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