We've all watched the play: The linebacker rushes through the line to tackle the quarterback, the two colliding as their helmets crash together, leaving one or both lying on the field, dazed and possibly unconscious.

Of all sports, football holds the highest incidence of concussion. Although collisions are an essential part of the sport, intentionally caused helmet-to-helmet collisions are now banned in most football leagues. Safety concerns include head trauma, repeated concussions, spinal cord injuries and even death. But these helmet collisions continue to occur.

In fact, reports indicate that the autopsied brains of some professional football and hockey players who experienced repeated hits to the head showed signs of severe and progressive brain damage. Meanwhile, recent studies with living animals suggest that the brain may respond to even mild concussive blows with inflammatory and other reactions that — while designed to spur healing — could also contribute to tissue damage.

And it's not just professional football. Research shows that at least 50 high school or younger football players in more than 20 states since 1997 have been killed or have sustained serious head injuries on the field.

Although the rate of concussion can be reduced through rule changes and proper tackling technique, there are debates as to whether helmet design may also reduce the incidence of concussion.

A new study suggests that not all football helmets are created equal. Researchers directly compared helmet designs, with hits measured during real-play conditions, and found that the Riddell Revolution helmet reduced concussion risk by 54 percent compared with the Riddell VSR4 model.

Here's how the study was conducted: From 2005 to 2010, a total of 1,833 football players from various collegiate teams were fitted with helmet-mounted accelerometer arrays (HIT System, Simbex) that collected data on the severity, frequency and location of impacts to the head during games as well as practices. The two helmets chosen for comparison — Riddell VSR4 or Riddell Revolution — were the only helmets designed to fit the HIT system.

During the study, 1,281,444 head impacts occurred (322,725 to players wearing the VSR4 helmet and 958,719 wearing the Revolution). However, different positions may be exposed to situations in which they are more vulnerable to head impacts (i.e. a kicker may get only a few hits, while a running back may get hundreds of hits during a season).

After making the adjustment for head impact exposure, the relative risk of sustaining a concussion in a Revolution compared with a VSR4 helmet was 46.1 percent lower. What this means is that although players in Revolution helmets experienced more impacts than those wearing VSR4 helmets, the Revolution-wearing players sustained fewer concussions (2.82 percent vs. 4.47 percent).

Importantly, a helmet modulates the energy transfer to the head during impact, which dictates the accelerations that the head will experience. These head accelerations result in transient intracranial pressure gradients and neural tissue strain responses and are correlated to risk for concussion.

While the two helmets used in this study were similar in design, the Revolution has 40 percent thicker foam or padding, making it stiffer, which translates to reduced head acceleration.

Currently, there are four top-rated five-star football helmets, including the Riddell 360, Rawlings Quantum Plus, Xenith X2 and Riddell Revolution Speed.

For all helmet types, those that reduce head acceleration will reduce risk of concussion. However, it just may be that some players are more susceptible to head injuries than others who may be more tolerant to them.