Assessing Injury Risk in the NFL

July 13, 2023

Written by Tom Christ, PT, DPT, OCS, FAAOMPT, @FantasyinjuryT

It’s a never-ending debate in the fantasy football community. Can we predict injury? Football is the most physical sport known to present mankind, and players are constantly getting injured. Assessing injury risk in the NFL can be a powerful way to build your fantasy football roster, but is it reliable? Below I will discuss what the research says and provide my own clinical experience.

As a doctor of physical therapy, much of my work clinically, and when writing and podcasting, is based on peer-reviewed evidence. Peer-reviewed evidence means that researchers have utilized the scientific method to conduct studies, and before these studies are published and used in practice, an intense review process takes place to ensure the study was performed correctly, with as little risk of bias as possible.

Humans are complex creatures, however, and even the best research to date leaves question marks when predicting injury. In short, we cannot perfectly predict injury, and the intent should not be to do so. Instead, we should identify factors that may predispose an athlete to future injury.1 These factors that may predispose an athlete are well-researched. I will share what the evidence says and provide my own clinical experiences to help fantasy football players best evaluate risk when building their fantasy football rosters.1,2

Intrinsic and Extrinsic Factors in Injury Risk In The NFL

Almost all research on injury risk cites intrinsic and extrinsic factors that may predispose an athlete to injury.1,2,3 An intrinsic factor is one within the individual themselves (age, level of conditioning), whereas an extrinsic factor is one outside of the player’s control (playing surface, time of season). These intrinsic and extrinsic factors are numerous, and some of which NFL fans will have no insight into the status of a particular player. This article will attempt to outline the most common factors and what we, as fans, have access to.

Within the categories of intrinsic and extrinsic factors, there are modifiable and non-modifiable. A modifiable risk factor is one that can be changed via training or another lifestyle change (ex. seeking psychological counseling). A non-modifiable risk factor is one that cannot be changed (ex. age). Be mindful, below is a non-exhaustive list, as the true list of factors that may influence injury is nearly infinite.

Intrinsic Factors Associated With Injury Risk In The NFL

Intrinsic Non-Modifiable Risk Factors For Injury

Age

Age is routinely cited as one of the strongest factors influencing injury.2-6 The age cutoff is not well defined, but 25 tends to be the line of demarcation, where below age 25, injury risk is lower, and healing is more efficient.3 As we age, the composition of tissues begins to change. Muscle begins to lose its elasticity and its tolerance to stretch and load; muscle begins to lose its ability to generate power at the same capacity, and the composition of collagen and other important cellular components of muscle begins to decline.7

Numerous studies cite age as a risk factor for various muscle injuries, including hamstring, calf, quad, and groin injuries.4,5,7 Julio Jones is a great example. Jones was dominant for much of his career. However, in his 30s, Jones has struggled to stay on the field as he has battled numerous hamstring injuries.

Interestingly, research on ligament injuries, particularly ACL and ankle sprains, suggests younger players are at more risk for ligament injury.6,8 Part of the reason is that younger people tend to have more mobile joints. As we age, the bony alignment of our joints changes, and more bone begins to develop in joints that routinely take on load. While this eventually leads to arthritis and stiffness, it does reduce the mobility of the joint, making it less likely for ligament sprains to occur. While the research on ankle sprains and ACL tears highlights youth as a risk factor, in general, older age lends an athlete more likely to get injured and to take longer to recover.

Clinical experience: This one is pretty obvious; the majority of my patients are older. Even those who are athletes, as they get older, will often state that they don’t recover as fast as they used to and that they used to be able just to go out and play but now need to be hyper-focused on their warm-up routine before playing.

Previous Injury

In addition to age, previous injury is the other most influential injury risk factor in the NFL.2-5 We see this all the time. An athlete suffers an injury in the pre-season, and it lingers all year long. Karadius Toney is a prime example, who had three separate lengthy absences from the field last season due to recurring hamstring injuries.

A prior hamstring injury increases the risk of a future hamstring injury by 2.7x. This number jumps to 5x when the initial injury occurs in the same season!5 Once again, see the Kadarius Toney example above. A study by Tyler and colleagues showed that 26% of athletes with a history of an ankle sprain suffered a subsequent ankle sprain, whereas only 11% of those with no history of ankle sprains suffered a sprain.9 Another study showed that 40% of athletes who suffer an ankle sprain develop a condition called “chronic ankle instability,” where they begin to suffer recurring ankle sprains.10 Similar trends exist for groin injuries, with a 29% chance of re-injury.11 Athletes returning from a calf injury are at higher risk for a subsequent injury within eight weeks of the initial injury.7 Shoulder dislocations are another injury that has a high recurrence rate. We saw this with Dalvin Cook over the past few seasons.

Some explanations can be found in the literature. Muscle strength imbalances are commonly cited as a risk factor for injury, as well as training load (see below), single-leg stability, and many other factors.5 Following a muscle injury, it takes several weeks of training for the muscle to fully regain its strength. In fact, typically, the injured portion of the muscle does not repair as strongly as it was before the injury. Athletes, especially NFL players, often return to the field well before their muscle has fully regained strength, thus putting them susceptible to another injury. Ligaments almost never truly heal, especially grade II-III injuries. The ligament’s role is to passively hold joints within their normal ranges of motion. If there is “laxity” or increased motion in a joint, usually due to loss of ligament stability, the joint is now more likely to move into excessive ranges that can cause further sprains.

But it’s not just the same injury that a prior injury increases the risk for. In movement science, there is a term called “regional interdependence.” This describes the relationship between movement and function in one body region and how it can influence movement in another region. Regional interdependence is particularly relevant with lower body injuries. The research suggests that ankle injuries, calf injuries, ACL injuries, and many other lower-body injuries can increase the risk for other different lower-body injuries.2,5 Athletes with a history of an ACL tear have a 70% increased risk for a hamstring injury on the same leg (Ex. Chris Godwin), while those who have had a calf injury have a 50% increased risk for a hamstring injury on the same leg.5 These are just a few examples of the influence of an injury in one body region on injury elsewhere. On the Fantasy Injury Team podcast, we routinely outline more examples of regional interdependence throughout the season.

Clinical Experience: Clinically, I constantly see the effects of the prior injury on regional interdependence. By far, the most common issue I see is previous ankle surgeries or sprains. While athletes often develop chronic ankle instability where the ankle is far too mobile, I believe this eventually leads to stiffness in the ankles over time. This would occur over time as the body lays down excessive scar tissue in an attempt to stabilize the joint, and the muscles become excessively tight to protect against the excessive motion. I see this literally every single day in practice! A new patient has a knee, hip, back, etc. injury that I can directly link to mechanical changes secondary to their ankle. If the ankle is too stiff, the body loses its shock absorption capability, and excessive loads go to the knees, hips, and upward. If the athlete is still experiencing ankle instability, they have lost the ability to properly stabilize and push off their ankle when running and cutting; therefore, excessive motion occurs in the leg, and overuse of muscles such as the hamstrings and groin occur.

Intrinsic Modifiable Risk Factors For Injury

Training load, Level of Conditioning, and Fatigue

Some studies cite training load as an extrinsic factor, but I see it more as an intrinsic factor as it is within ones own control. There is ample research on appropriate training loads, macro and micro programming for athletes to prepare for the season. The depth of which is outside the scope of this article, and we, as fans, don’t know the details of athletes’ training programs. However, I want to focus on what we will know. We know that when an athlete is injured, particularly a lower-body injury, they cannot train to the same level as when they are not injured. Therefore, it is plausible that this is a major factor in re-injury upon return to play.

Load management is a term we constantly hear in sports, and for a good reason. When an athlete has not played in several weeks, they are not as conditioned as before the injury, and ramping up the snap percentage too fast will increase injury rates. The reason is a combination of muscle strength/endurance and overall fatigue. Strength imbalances are predictive of injury, and fatigue has been long studied as a risk factor for injury.5,7,8 As athletes fatigue, studies show changes in their landing and cutting mechanics, putting them at risk for lower body injuries.8

Let’s take Sterling Shepard as an example. Shepard suffered an Achilles injury late in 2021. The Achilles repair rehab protocol is very long, and often athletes never fully regain the strength and conditioning in the affected leg. In 2022, only about 9-10 months after his Achilles injury, Shepard tore his ACL on the same leg on the very last play of the game from a non-contact mechanism. While we don’t know for certain, it is reasonable to assume that his leg as a whole was not at 100% strength and muscular endurance coming off the Achilles tear and that the fatigue in that leg at the end of the game may have contributed to the ACL injury.

Clinical Experience: There are numerous return-to-sport tests that we can do in the clinic to help predict if our athletes are ready to play. However, hardly any of these tests involve components of fatigue. I believe fatigue is the bigger factor here, as athletes’ strength, motor coordination, and overall movement mechanics will change with fatigue. From a fantasy football perspective, we should assume that athletes coming off an injury that has kept them out for 3+ weeks will not be as conditioned, and if their teams are smart, they should ease the athlete back into the gameplay over the first few weeks after injury. This may present as either a reduced snap count in the first game or two after injury (leading to less opportunity to score fantasy points) or an increased risk for re-injury in that first game or two back from injury.

Motor Control

Motor control deficiencies can impact running and cutting mechanics, increasing the load on particular joints or muscles, and contributing to injury.3,7,8 In particular, poor glute and core muscle activation often lead to overuse of the hamstrings and groin muscles. They will impact an athlete’s ability to control their leg position when cutting and landing, which could influence injury. Sometimes it’s a chicken or egg scenario. Did the athlete have poor motor control that led to the injury? Or did a prior injury alter their motor control which is now feeding future injuries? It goes both ways.

Unfortunately, as fans, we have no insight into an athlete’s motor control outside of training videos. This one will be hard to put into practice for fantasy football. Fortunately, in modern-day social media, athletes are constantly posting training and practice videos, and trained movement analysis specialists, such as physical therapists, physicians, athletic trainers, and other medical professionals, can identify when motor control issues are present.

Clinical Experience: As mentioned above, it’s typically the glutes and core that I see not performing properly. I have worked with an active NFL wide receiver who literally could not activate his glute muscles to save his life. Common patterns I see are underactive glute muscles leading to a combination of overactive hamstrings and back muscles to compensate. This contributes to hamstring injuries, back spasms, and other lower-body injuries. I also see poor core strength leading to overuse of the hip flexors, groin muscles, and back muscles to compensate.

Range of Motion

Surprisingly range of motion is not as discussed as a major risk factor for injury as often as you would think; however, it has been linked in some studies. Groin injuries appear to be influenced by a lack of hip motion, and ankle stiffness can also be a factor in a lower-body injury.2,12

As fans, we won’t know how an athlete’s range of motion is, though we do know that range of motion decreases with age and often decreases following surgery. Following any major surgery regaining full range of motion at the joint is paramount. Without fully regaining range of motion, compensations elsewhere in the body are likely to occur. JK Dobbins last season was a prime example. Dobbins struggled to regain knee flexion range after his complicated knee surgery. This led to a second procedure to clean out excessive scarring and restore full range.

Ankle surgeries often lead to lingering stiffness and plausibly could contribute to future injury. This season players like Tony Pollard and Cooper Kupp are returning from major ankle surgery, and while their production levels should not be affected, their injury risk may be elevated.

Clinical Experience: Stiff ankles are a problem! As I mentioned above, I see this every day. A stiff ankle changes shock absorption and mechanics up the chain, contributing to injuries at other joints. Not every time, so players like Pollard and Kupp are not guaranteed to get injured, but the risk is elevated. Sometimes the healthiest, hardest working person still has difficulty regaining range of motion after surgery (especially if they are older!). Ideally, we catch it early in the rehab process and utilize techniques to restore range, but sometimes they need a second procedure, such as manipulation under anesthesia or arthroscopic cleanout.

Psychological State and Sleep

I combined these into one since we will not know an athlete’s psychological state or sleep hygiene. Psychological state is CONSTANTLY cited as a risk factor for injury.2,3,13 In particular, disagreements with coaching philosophy, game plans, and relationship stressors are cited as contributing to injury.3,13 Sleep issues will contribute to fatigue, which is discussed above, as well as mental alertness, focus, and many other negative consequences.3

Clinical Experience: Psychological stressors and lack of sleep are incredibly influential factors in injury and recovery. In fact, psychological state is MORE predictive of chronic pain than any tissue injury seen on X-ray or MRI. We don’t know NFL players’ psychological or sleep conditions, so this will not help build our rosters, but it is important to note how these impact injury risk in the NFL.

BMI

I’m not overly concerned with BMI for injury risk in the NFL because they are all enormous, but BMI has been cited in the medical literature as a risk factor for ankle sprains.6 The study referenced uses a BMI >29 as influential on injury.

Clinical Experience: I often see heavier-set people deal with more injuries and have a harder time recovering; however, NFL players are elite athletes. I do not feel we need to use BMI as a factor when evaluating injury risk, but I can see the argument for someone who is a little more concerned about a heavier receiver or running back potentially dealing with more injury.

Extrinsic Non-Modifiable Risk Factors For Injury

Sport and Position

For the purpose of an NFL athlete, they all are playing football, the most violent sport known to mankind, making NFL player risk higher than most sports. Outside of a few rare situations, they don’t change their position. Running backs have the highest injury rate as they take the more extensive beating. Receivers also have a high injury rate.

Clinical Experience: Athletes of any sport can get injured, but football season is always a busy time in the PT clinic!

Time of Season

Injury rates tend to be higher in the preseason and first few weeks of the season, but can happen at any time.7,14 Rates may be higher earlier in the year, secondary to player conditioning. Interestingly, the first four weeks of the NFL season after the canceled preseason due to COVID-19 saw a tremendous jump in injury rates.14 This was also seen in 2011 after the NFL lockout abbreviated the preseason.

Higher injury rates early in the season are attributed to training load and conditioning (see above). Some athletes return to camp not as well-conditioned as they finished the prior season. Most train hard in the offseason, but there is no way to acclimate to football without playing football.

Clinical Experience: I am constantly treating athletes of all sports who get injured at the beginning of their season. The average individual does not understand the importance of load management and gradually increasing workload, and often teams and sports will jump right in on day one. It’s up to the athlete and their training staff to ensure they are training properly leading up to the season to mitigate the risk of conditioning-related injury.

Extrinsic Modifiable Risk Factors For Injury

Playing Surface

This one may or may not be modifiable, depending on who you ask and who is in charge. A long debated topic in NFL player injury risk is grass vs. turf. In 2022 the NFL released data from the 2018-2021 season showing no difference in injury rates on turf vs. grass. However, players have long stated they feel grass is safer.

In April of 2023, the NFLPA released a statement contradicting the NFL’s 2022 data, stating that the NFL utilized 2021 as their primary data set (a season where injury rates on turf and grass were essentially the same). However, 2021 appears to be an outlier year, whereas many years before 2021, injury rates on turf were much higher.

It makes sense that turf is more conducive to injury. Underneath grass is dirt or mud, which can give as a player’s cleats can slide through it, potentially preventing the foot from getting caught. Turf does not provide this benefit. When a cleat gets stuck in the turf, the turf will not give, which can contribute to lower body injuries.

Clinical Experience: To be honest, I have not seen too many patients who report turf as a factor in their injury. That said, I certainly see the argument NFL players make in favor of natural grass for the above reasons.

Inciting Event Associated With Injury Risk In The NFL

While these intrinsic and extrinsic factors may increase an athlete’s risk for injury, they themselves do not cause injury. Researchers cite what is called an “inciting event,” also known as the actual occurrence of the injury. This inciting event can be when an athlete tears their ACL from a non-contact cutting mechanism, and it can be when their throwing arm gets hit during the follow through leading to a UCL tear or any other mechanism of injury.3 The intrinsic and extrinsic factors may predispose the athlete to injury, but without the inciting event, the injury will not happen.

Conclusion

There are many factors that may influence NFL player injury risk. Age and previous injury are by far the most referenced and most influential factors and the best tools fantasy football players have to assess injury risk. Many other factors exist, some of which we have insight into, some we do not. At the end of the day, we cannot fully predict injury, but we can use the factors listed above to gauge risk. From there, fantasy players can weigh the risk vs. reward of a particular player when creating their rosters.

Age is easy for fantasy players to track as it is listed on their profiles on every sports website. Resources such as Draft Sharks and Player Profiler provide medical history as well, which fantasy players can utilize. As always, the Fantasy Injury Team is here to help fantasy players put all the pieces together to best understand how all of these factors may influence a player’s injury risk going forward.

References

1: Ruddy JD, Cormack SJ, Whiteley R, Williams MD, Timmins R. Gand Opar DA (2019) Modeling the Risk of Team Sport Injuries: A Narrative Review of Different Statistical Approaches. Front. Physiol. 10:829. doi: 10.3389/fphys.2019.00829

2: Van Eetvvelde H, Mendonca L, Ley C, Seil R, Tischer T. Machine learning methods in sport injury prediction and prevention: a systematic review. J Exp Orthop. 2021;8(27).

3: Sigurdson H, Chan J. Machine Learning Applications to Sports Injury: A Review. icSPORTS. 2021: 157-168.

4: Alabbad M, Nuhmani S, Muaidi Q. Groin Injuries In Soccer: Incidence, Prevalence, and Risk Factors. J Phys Edu Research. 2019;6. 16-21.

5: Green B, Lin M, McClelland J, et al. Return to Play and Recurrence After Calf Muscle Strain Injuries in Elite Australian Football Players. Am. J. Sports. Med. 2020;48(13):3306-3315.

6: Delahunt E, Remus A. Risk Factors for Lateral Ankle Sprains and Chronic Ankle Instability. J Ath Train. 2019;54(6):611-616.

7: Green B, Pizzari T. Calf muscle strain injuries in sport: a systematic review of risk factors for injury. Br. J. Sports. Med. 2017;51:1189-1194.

8: Kunas, Kajeniene A. Risk Factors For Anterior Cruciate Ligament Injuries In Football Players: A Systematic Literature Review. 2019.

9: Tyler TF, McHugh MP, Mirabella MR, Mullaney MJ, NicholasSJ. Risk factors for noncontact ankle sprains in high school football players: the role of previous ankle sprains and body massindex. Am J Sports Med. 2006;34(3):471–475.

10: Doherty C, Bleakley C, Hertel J, Caulfield B, Ryan J, Delahunt E. Recovery from a first-time lateral ankle sprain and the predictors of chronic ankle instability: a prospective cohort analysis. Am J Sports Med. 2016;44(4):995–1003

11: Núnez J, Fernandez I, Torres A, et al. Strength Conditioning Program to Prevent Adductor Muscle Strains in Football: Does it Really Help Professional Football Players? Int J Environ Res Public Health. 2020;17(17):6408.

12: Candela V, Carli A, Longu U, et al. Hip and Groin Pain in Soccer Players. Joints. 2021;7(4):182-187.

13: Arvinen-Barrow, M., & Walker, N. (2013). The Psychology of Sport Injury and Rehabilitation. Routledge Ba, H. (2020). Medical Sports Rehabilitation Deep Learning System of Sports Injury Based on MRI Image Analysis. Journal of Medical Imaging and Health Informatics, 10(5), 1091–1097. https://doi.org/10.1166/ jmihi.2020.2892

14: Baker H, Pirkle S, Cahil M, Reddy M, Portney D, Athiviraham A. Injury Rate in National Football League Players Increased Following Cancellation of Preseason Games Because of COVID-19. Arth Sport, Med, Rehabil. 2021;3(4):1147-1154.