Most EMS providers recognize certain mechanisms almost automatically. A significant fall gets our attention. So does a high-speed vehicle collision, axial loading or another mechanism with the potential to produce serious injury.
But standing on the sidelines of a high school football game raises an interesting question.
A player running at full speed can plausibly be moving in the neighborhood of 17 mph when he hits another player. As it happens, about 17 mph is also how fast a person is traveling when he hits the ground after falling 10 feet.
So, are those mechanisms comparable?
I went looking for an answer. The short version is yes, in one interesting way, and no, in several important others.
| MORE: What does mechanism of injury tell us?
Why 10 feet?
The 2021 National Guideline for the Field Triage of Injured Patients identifies a fall greater than 10 feet, at any age, as a moderate-risk mechanism for serious injury. Importantly, this is a trauma triage criterion, not a spinal immobilization criterion. A 10-foot fall does not automatically mean a patient has a spinal injury or requires spinal precautions.
But it gives us a familiar mechanism for comparison.
Using basic free-fall physics, a person falling 10 feet reaches the ground at approximately 17 mph.
Now consider a football player. An athlete who runs 40 yards in 5 seconds averages about 16.4 mph over the entire distance. Because he starts at zero and accelerates, his peak speed has to be higher than that average.
That does not mean every high school football player runs 17 mph. It simply demonstrates that 17 mph is a plausible speed for an athlete who has enough room to accelerate.
For the same athlete, 17 mph represents the same amount of translational kinetic energy whether he is moving vertically toward the ground or horizontally across a football field. That creates an interesting comparison, but it is also about where the direct comparison should stop.
The same speed does not mean the same collision
A person falling 10 feet generally encounters something that does not move very much: the ground.
A football player usually encounters another football player. That player can move backward, rotate, fall or otherwise carry energy away from the collision. Helmets and shoulder pads affect how forces are distributed. The angle of contact and body position matter. After the initial collision, one or both players may then strike the ground.
So, saying that a 17-mph football collision is equivalent to a 10-foot fall would go too far. A more accurate statement is that some high-speed football collisions can begin with a pre-impact velocity and amount of translational kinetic energy comparable to those present immediately before a 10-foot fall. What happens to that energy after contact can be very different.
The same caution applies when adding the speeds of two players. If two athletes are each running 15 mph toward one another, their closing speed is 30 mph. But neither player necessarily experiences the equivalent of hitting a fixed object at 30 mph. Closing speed tells us how quickly the distance between them is disappearing, not the force experienced by either athlete.
Football-related head injury
Researchers attached instruments to the helmets of 35 varsity high school football players and analyzed 19,224 impacts over a season. Among offensive skill-position players, they reported a change in head velocity of 11.01 meters per second, or about 24.6 mph. See the study by Broglio and colleagues.
It does not mean the players were running 25 mph. It is a change in velocity, or delta-V. In practical terms, it describes how much the motion of the head changed as it was rapidly slowed, stopped or redirected during the impact.
The study also found that impacts to the top of the helmet produced the greatest linear acceleration and impact-force magnitude.
Those findings help put the abruptness of some football impacts into perspective, but we should not make them say more than they do. Broglio studied head-impact biomechanics, not cervical-spine loading. The 24.6-mph delta-V is not a spinal injury threshold or an indication for spinal immobilization. It is evidence that substantial changes in head motion can occur over a very short period during football contact.
“Football collision” is not much of a mechanism description
This may be the most useful takeaway for EMS.
Two linemen making contact immediately after the snap and a receiver being hit by a safety after both have sprinted downfield are both technically football collisions. Biomechanically, they are very different events.
So are a shoulder-to-shoulder hit, crown-of-the-helmet contact with axial loading, a player being struck from the side and an athlete being driven head-first into the ground.
Instead of documenting or communicating simply “injured during football,” we may be better served by describing what actually happened. How much room did the athlete have to accelerate? Where was the initial contact? What direction did the force travel? What was the position of the head and neck?
Was there evidence of axial loading? Was the player thrown or driven into the ground? What happened immediately afterward?
Those details tell us much more about mechanism than the sport itself.
What about spinal precautions?
There is another complication: Spinal motion restriction (SMR) does not mean exactly the same thing everywhere.
National sports-medicine literature commonly uses spinal motion restriction broadly enough to include several techniques and devices, including rigid devices. The 2020 consensus recommendations for the spine-injured football athlete specifically acknowledge variation in SMR practices and the importance of state and local EMS protocols.
In South Carolina’s EMS Clinical Operating Guidelines, where I practice, the state distinguishes SMR from spinal immobilization. Providers should be cautious about applying terminology from national literature directly to their own protocols.
Ultimately, the athlete’s clinical presentation matters more. The 2020 consensus recommendations identify findings such as altered level of consciousness, spinal pain or tenderness, loss of cervical range of motion, neurologic complaints or findings, and spinal deformity as reasons for concern.
In other words, significant football contact matters, but mechanism simply does not exist in isolation from the clinical assessment.
The fact that an athlete can enter a collision with energy comparable to that developed during a 10-foot fall does not establish that he has a spinal injury. Nor does it create a new indication for a backboard, scoop stretcher, cervical collar or any other intervention.
It does suggest that we should not dismiss a significant open-field collision simply because violent contact is expected in football.
So, what does the comparison tell us?
Probably less than a new protocol, but more than a piece of trivia.
A 10-foot fall and a high-speed football collision can begin with similar velocity and translational kinetic energy, then become very different biomechanical events. The comparison gives us context for appreciating the energy involved. It does not make the treatment decision for us.
For EMS providers, the practical lesson may be more simple: Describe the mechanism you actually saw.
“Football injury” tells us very little. A full-speed open-field collision, crown-of-the-helmet impact, axial load and subsequent head-first impact with the ground tells us considerably more.
Mechanism informs suspicion; clinical assessment and protocols guide treatment.
