The head is a relatively heavy appendage (about 10% of body weight) atop a narrow, highly mobile stalk: the neck. When a football player takes a clean, by-the-book hit to the torso, the force from the incoming player is transmitted throughout the body. The legs can handle it: they have a lot of very strong musculature to keep them in place. The arms can handle it: the players have well-developed shoulders as well as an instinctive response to bring everything close in to the torso in response to trauma. But the head is just wobbling up there atop the neck, as we can see when it flicks rapidly back-and-forth from a hit that lands half-a-player's-height away.
The whiplash effect is even more pronounced when the player gets hit from two sides in rapid succession. We've all seen the replays that get worse with each viewing, as the player's head whips from one side to the other to another after getting hit first from the front and then from the side. The same thing can happen when a player lands on his back on a hard surface, like in ice hockey: his head hits the ground with the rest of his body, bounces up and hits the ground again.
"The greatest threat to our game is the risk of concussion," says Arlington (TX) Martin High School football head coach Bob Wager. Sport and strength coaches have to look beyond protective equipment to how they can proactively minimize concussions.
If impacts to the head were the only cause of concussion, advances in helmet technology would have taken a larger bite out of the concussion rate in football, hockey, lacrosse, soccer and other contact sports. But hits to the body also cause concussions, and while pads protect the impact sites, they cannot protect the brain.
Whiplash Effect Drives Concussions in Contact Sports
Nature provides us a built-in helmet: our skulls. Wearing a helmet for sports or recreational activities adds another protective layer between our brain and anything - another person, a projectile, the ground - that hits our head.
Both the natural and man-made protection, though, only attenuates the trauma to our brain from things that directly impact the head from the outside. Any collision against the body or the head can cause the brain to move around within the skull cavity. If there is enough force, the brain will bump, slam and rattle against the internal walls of the skull. That's the downside of such strong armor: because the skull is hard enough to protect the brain from the outside world, it's also hard enough to cause damage if the brain itself is the object having the collision.
The whiplash effect is behind much of the harm the brain experiences from hits to the body.
The head is a relatively heavy appendage (about 10% of body weight) atop a narrow, highly mobile stalk: the neck. When a football player takes a clean, by-the-book hit to the torso, the force from the incoming player is transmitted throughout the body. The legs can handle it: they have a lot of very strong musculature to keep them in place. The arms can handle it: the players have well-developed shoulders as well as an instinctive response to bring everything close in to the torso in response to trauma. But the head is just wobbling up there atop the neck, as we can see when it flicks rapidly back-and-forth from a hit that lands half-a-player's-height away.
The whiplash effect is even more pronounced when the player gets hit from two sides in rapid succession. We've all seen the replays that get worse with each viewing, as the player's head whips from one side to the other to another after getting hit first from the front and then from the side. The same thing can happen when a player lands on his back on a hard surface, like in ice hockey: his head hits the ground with the rest of his body, bounces up and hits the ground again.
Increasing Neck Strength can Reduce Whiplash Effect and Concussion Risk
Collins et al (2014) examined the relationship between neck characteristics and concussions in high school athletes, and showed how the necessary assessments and training could be performed with staff and equipment high schools already have. Among nearly 7,000 male and female basketball, soccer and lacrosse players, Collins' research group found that neck strength was a statistically significant predictor of concussions. Accounting for sport and gender, they found that every 1-pound increase in neck strength reduced the risk of concussion by 5%.
Collins et al used isometric neck strength as their measure. This was partly due to ease of measurement and to establish a reliable, valid and convenient method for training staff to quantify neck strength. But isometric strength may be one of the most important attributes for an athlete's ability to counteract the whiplash forces that lead to concussions.
Isometric strength reflects the ability of the muscle to control movement against an external force. An athlete with greater isometric neck strength may be able to control or dissipate impact forces to the head or body, limiting the amount of whiplash-style movement and, therefore, impact between the brain and the skull. Indeed, Kadlec and Snyder (2018) found that only eight sessions of isometric neck strength training were enough to reduce head and neck movement following an unexpected impact. Similarly, Hamlin, et al (2020) showed improvements in maximal isometric contraction after six weeks of training.