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The Injury Rate in National Football League Players Increased Following Cancellation of Preseason Games Because of COVID-19

Open AccessPublished:May 28, 2021DOI:https://doi.org/10.1016/j.asmr.2021.05.002

      Purpose

      To investigate the injury rate in National Football League (NFL) athletes during the first 4 weeks of the 2020 NFL season.

      Methods

      This study was a retrospective review of all NFL players who were placed on the injury report during the preseason and the first 4 weeks of the regular season from the 2016-2017 through the 2020-2021 NFL regular seasons. Players’ dates of injury were cross-referenced with an absence of statistics from the respective games for which they were ruled out so as to ensure accuracy. Injury rates were calculated per 1,000 athletic exposures. Relative risk with 95% confidence intervals compared injury rates between the 2 cohorts.

      Results

      Over the course of the study period of 4 NFL seasons, 3,025 injuries were reported. Of the 3,025 injuries reported, 582 (19%) occurred during weeks 1-4 of the 2020-2021 regular season, whereas 1,292 (53%) occurred during preseason weeks 1-4, and 1,151 (38%) occurred during regular-season weeks 1-4 of NFL seasons 2016-2017, 2018-2019, and 2019-2020. There was a significant increase in the injury rate during weeks 1-4 of the 2020-2021 regular season for all comparisons with the injury rate both during the preseasons and the regular seasons of 3 recent past NFL seasons.

      Conclusions

      The rate of injury in NFL players during weeks 1-4 of the 2020-2021 regular seasons was significantly higher than during 3 recent past NFL preseasons and regular seasons.

      Level of Evidence

      Level IV, diagnostic case series.
      Because of the rising number of positive Covid-19 tests observed in National Football League (NFL) players during the summer of 2020, the NFL suspended the 2020 preseason on July 21, 2020.
      • Pickman B.
      Report: NFL Scraps 2020 Preseason Amid COVID-19 Pandemic. Sports Illustr 2020; July 21.
      Suspension of play based on concern regarding rising numbers of cases of Covid-19 in the United States was widespread and not limited to the NFL; similar trends were observed across all sports and levels, including high school, collegiate and professional levels. To mitigate potential exposures to Covid-19, NFL team training camp roster sizes were limited to 80 players.
      • Pickman B.
      Report: NFL Scraps 2020 Preseason Amid COVID-19 Pandemic. Sports Illustr 2020; July 21.
      Typically, the NFL preseason serves as the primary time for preparing athletes for the rigors of the upcoming NFL season. However, given this unprecedented stoppage of preseason training and teams’ inability to continue with practice and games due to social-distancing precautions, athletes were forced to train and condition on their own. We speculated that in the absence of organized team activities, athletes developed sports deconditioning.
      Previous studies have demonstrated that fatigue and deconditioning may place athletes at a higher risk for injury. The International Olympic Committee identified absolute load, calendar congestion and psychological load to be closely associated with injury risk through a variety of mechanisms.
      • Mack C.D.
      • Kent R.W.
      • Coughlin M.J.
      • et al.
      Incidence of lower extremity injury in the National Football League: 2015 to 2018.
      Excessive training that exceeds the body’s loadbearing capacity causes microtrauma to tendons, muscles and bones and is the cause of overuse injuries.
      • Soligard T.
      • Schwellnus M.
      • Alonso J.M.
      • et al.
      How much is too much? (Part 1): International Olympic Committee consensus statement on load in sport and risk of injury.
      • Bennell K.L.
      • Malcolm S.A.
      • Wark J.D.
      • Brukner P.D.
      Models for the pathogenesis of stress fractures in athletes.
      • Dye S.F.
      The pathophysiology of patellofemoral pain: A tissue homeostasis perspective.
      • Edwards W.B.
      Modeling overuse injuries in sport as a mechanical fatigue phenomenon.
      • Magnusson S.P.
      • Langberg H.
      • Kjaer M.
      The pathogenesis of tendinopathy: Balancing the response to loading.
      • Warden S.J.
      • Davis I.S.
      • Fredericson M.
      Management and prevention of bone stress injuries in long-distance runners.
      In light of these findings that highlight the association between fatigue and risk of injury, investigating modifiable causes influencing athletes’ levels of fatigue is a critical step in reducing risk of injury. The purpose of this study was to investigate the injury rate in NFL athletes during the first 4 weeks of the 2020 NFL season. Our hypothesis was that the observed injury rate during the first month of the 2020-2021 NFL season would be significantly higher when compared to past seasons.

      Methods

      Data Collection

      This study was a retrospective review of all NFL players who were placed on the injury report during the preseason and the first 4 weeks of the regular season from the 2016-2017 through the 2020-2021 regular NFL seasons. The data were compiled using publicly available injury reports (Appendix). The sources used publish a weekly injury reports detailing the names of the players injured, their teams and a brief description of each injury. At least 2 different sources were used to cross-reference injury information. To verify each player’s date of injury, we confirmed that each player’s reported injury date corresponded to an absence of statistics from the respective games for which he was ruled out. These methods are in accordance with previously published protocols.
      • Conte S.A.
      • Thompson M.M.
      • Marks M.A.
      • Dines J.S.
      Abdominal muscle strains in professional baseball: 1991-2010.
      • Erickson B.J.
      • Gupta A.K.
      • Harris J.D.
      • et al.
      Rate of return to pitching and performance after Tommy John surgery in Major League Baseball pitchers.
      • Gibson B.W.
      • Webner D.
      • Huffman G.R.
      • Sennett B.J.
      Ulnar collateral ligament reconstruction in Major League Baseball pitchers.
      • Makhni E.C.
      • Lee R.W.
      • Morrow Z.S.
      • Gualtieri A.P.
      • Gorroochurn P.
      • Ahmad C.S.
      Performance, return to competition, and reinjury after Tommy John surgery in Major League Baseball pitchers: A review of 147 cases.
      • Marshall N.E.
      • Jildeh T.R.
      • Okoroha K.R.
      • Patel A.
      • Moutzouros V.
      • Makhni E.C.
      Implications of core and hip injuries on Major League Baseball pitchers on the disabled list.
      When collecting data, we noted that the 2017-2018 records were incomplete, so we excluded them from the study. We thought that data from 3 recent past seasons were adequate to compare data from 2020.
      Team records available for individual team websites were used to collect demographic information. Our dataset included each player’s name, position, team, pathology, age at injury, date of injury, and season. Data for the 2020 season were collected prospectively, so we were unable to determine games missed due to injury because the 2020 NFL season was ongoing when this study was performed.

      Definitions

      Reportable injuries were based on the following criteria: that the injury necessitated a team physician’s referral or emergent care and that it resulted in missed athletic activity. An athlete-exposure (AE) was defined as 1 athlete’s participation in 1 game in which he was exposed to potential injury.

      Data and Statistical Analysis

      Data analysis was conducted using SPSS 25 (SPSS, Chicago, IL). Injury rates were calculated per 1,000 AEs using the following calculations: for the first 3 preseason games where NFL teams carry 90 players on the roster (total number of injuries × 1,000/total number of AEs (AEs = 90 players ∗ 32 NFL teams ∗ number of games)); for the fourth preseason game, where NFL teams cut the roster to 75 players (total number of injuries × 1,000/total number of AEs (AEs = 75 players ∗ 32 NFL teams ∗ number of games)); and for the regular-season games (total number of injuries × 1,000/total number of AEs (AEs = 53 players ∗ 32 NFL teams ∗ number of games)). Risk ratio with 95% confidence intervals (CIs) compared injury rates between the 2 cohorts. Risk ratios were calculated by comparing both weeks 1-4 from the preseason and the regular NFL seasons in 2016-2017, 2018-2019 and 2019-2020 to the 2020-2021 season. Week 1 of the 2020-2021 NFL season was compared to both past preseason and regular-season week 1; this method of comparison was continued for weeks 2-4. Continuous variables were statistically compared using a 2-tailed t test, whereas categorical variables were compared using the χ2 test. Statistical significance was set at p ≤ 0.05.

      Results

      Over the course of the study period of 4 NFL seasons, 3,025 injuries were reported. Of those, 582 (19%) occurred during weeks 1-4 of the 2020-2021 regular season, while 1,292 (53%) occurred during preseason weeks 1-4, and 1,151 (38%) occurred during regular-season weeks 1-4 of NFL seasons 2016-2017, 2018-2019 and 2019-2020 (Table 1) (Fig 1). There was a significant increase in the injury rate during weeks 1-4 of the 2020-2021 regular season for all comparisons with the injury rate, both during the preseason and the regular season of the 3 recently past NFL seasons (Table 2).
      Table 1National Football League Injuries During Preseason and Regular Seasons Weeks 1-4 From 2016-2020
      WeekYear
      2016201820192020
      Preseason week 16317695Canceled
      Preseason week 277138228Canceled
      Preseason week 3112120102Canceled
      Preseason week 4479737Canceled
      Preseason Total299 (42%)531 (57%)462 (58%)0
      Regular season week 14810076141
      Regular season week 21779593159
      Regular season week 3999474136
      Regular season week 48911195146
      Regular season total413 (58%)400 (43%)338 (42%)582
      Total712931800582
      Figure thumbnail gr1
      Fig 1National Football League injures during preseason and regular seasons weeks 1-4 from 2016-2020.
      Table 2National Football League Injuries per Athlete Exposure During Preseason and Regular Seasons Weeks 1-4 From 2016-2020
      Injuries per 1000 Athletic ExposureRelative risk RatioP Value
      2016-20192020
      Preseason week 12.4Canceled2.140.001
      Preseason week 23.2Canceled1.820.001
      Preseason week 32.4Canceled2.070.001
      Preseason week 41.9Canceled4.090.001
      Regular season week 12.85.21.880.01
      Regular season week 24.55.91.310.01
      Regular season week 33.35.01.530.01
      Regular season week 43.65.41.480.01
      Positional breakdowns demonstrated that wide receivers, safeties and linebackers sustained the most injuries during the study period (Table 3). Most of the reported injuries were to the knee 473 (16%), hip/groin 347 (11%) or ankle 316 (10%) (Table 4). The majority of injuries occurred secondary to player contact: 2,151 (71%). Undisclosed injuries identified numbered 343 (11%).
      Table 3Positional Breakdown of Injuries
      Positional Breakdown
      Offense (quarterback)2016201820192020Total
      Quarterback222022973
      Runningback65978845295
      Wide receiver9713810295432
      Tight end62646634226
      Center142014957
      Offensive tackle41836252238
      Guard29432830130
      Fullback025310
      Defense2016201820192020Total
      Defensive tackle90549539278
      Defensive end23634047173
      Linebacker10311910279403
      Cornerback44776277260
      Safety11713910856420
      Special teams2016201820192020Total
      Kicker4125627
      Long snapper00112
      Table 4Injuries in National Football League Games by Season, Anatomic Site and Injury Mechanism
      Season and Anatomic siteNumber of Injuries (per 1000 AEs)Injuries per 1000 AEs
      ContactNoncontactOveruseTotal
      Weeks 1-4 of 2016-2017 Preseason and Regular Season
      Hip/groin1921101310.46
      Upper Leg/thigh2112220.08
      Knee117001170.41
      Lower leg/Achilles11924440.15
      Ankle8300830.29
      Foot/toes2800280.10
      Back2800280.10
      Biceps00000.00
      Rib Fracture1100110.04
      Collarbone10010.00
      Concussion6100610.21
      Elbow1500150.05
      Finger10010.00
      Hand2200220.08
      Illness06060.02
      Neck90090.03
      Pectoralis Major27090.03
      Toe90090.03
      Shoulder6000600.21
      Sports Hernia00000.00
      Triceps30030.01
      Undisclosed5000500.18
      Total551251367122.50
      Season and Anatomic siteNumber of Injuries (Injuries per 1000 AEs)Injuries per 1000 AEs
      ContactNoncontactOveruseTotal
      Weeks 1-4 of 2018-2019 preseason and regular season
      Hip/groin24509830.29
      Upper leg/thigh0121091210.42
      Knee159001590.56
      Lower leg/Achilles23618470.16
      Ankle9400940.33
      Foot/toes4600460.16
      Back0210210.07
      Biceps02020.01
      Rib fracture1300130.05
      Collarbone00000.00
      Concussion6300630.22
      Elbow1400140.05
      Finger650110.04
      Hand1600160.06
      Illness0160160.06
      Neck70070.02
      Pectoralis major60060.02
      Toe1000100.04
      Shoulder6300630.22
      Sports hernia00000.00
      Triceps03030.01
      Forearm40040.01
      Undisclosed132001320.46
      Total6801151369313.26
      Season and Anatomic siteNumber of Injuries (Injuries per 1000 AEs)Injuries per 1000 AEs
      ContactNoncontactOveruseTotal
      Weeks 1-4 of 2019-2020 preseason and regular season
      Hip/groin202222640.22
      Upper leg/thigh133940920.32
      Knee108001080.38
      Lower leg/Achilles21260470.16
      Ankle8100810.28
      Foot/toes3700370.13
      Back0230230.08
      Biceps03030.01
      Rib fracture60060.02
      Collarbone90090.03
      Concussion6500650.23
      Elbow1100110.04
      Finger1300130.05
      Hand1580230.08
      Illness06060.02
      Neck1700170.06
      Pectoralis major60060.02
      Toe60060.02
      Shoulder5400540.19
      Sports hernia00000.00
      Triceps00000.00
      Forearm00000.00
      Undisclosed129001290.45
      Total611127628002.81
      Season and Anatomic siteNumber of InjuriesInjuries per 1000 AEs
      ContactNoncontactOveruseTotal
      2020-2021
      Hip/groin211038690.64
      Upper leg/thigh01378910.84
      Knee26630890.82
      Lower leg/Achilles10260360.33
      Ankle5710580.53
      Foot/toes2000200.18
      Back18090.08
      Biceps30030.03
      Rib fracture1800180.17
      Collarbone20020.02
      Concussion2200220.2
      Elbow90090.08
      Finger1500150.14
      Hand50050.05
      Illness0330330.3
      Neck80080.07
      Pectoralis major80080.07
      Toe1100110.1
      Shoulder4100410.38
      Sports hernia02020.02
      Triceps01010.01
      Undisclosed3200320.3
      Total3091571165825.4
      AE, athlete exposure.

      Discussion

      The most important finding of this study was that the injury rate during weeks 1-4 of the 2020-2021 NFL season was significantly higher than the injury rates during weeks 1-4 of the 2016-2017, 2018-2019 and 2019-2020 NFL preseasons and regular seasons. The findings of our study confirmed our hypothesis that players were at a higher risk of injury during the early 2020-2021 regular season following cancellation of preseason games due to Covid-19. Our findings highlight the importance of the NFL training camp in preparing NFL athletes for the rigors of the NFL regular season and its influence on injury prevention.
      Similar to the findings of Feeley et al.
      • Feeley B.T.
      • Kennelly S.
      • Barnes R.P.
      • et al.
      Epidemiology of National Football League training camp injuries from 1998 to 2007.
      and Elliott et al.,
      • Elliott M.C.
      • Zarins B.
      • Powell J.W.
      • Kenyon C.D.
      Hamstring muscle strains in professional football players: A 10-year review.
      we observed that more injuries occurred during the first 2 weeks of the NFL preseason (777) (60%) when compared with the second 2 weeks (515) (40%). This trend was noted to continue, although less dramatically, during the 2020-2021 regular season; 300 (52%) injuries occurred during the first 2 weeks, whereas 282 (48%) occurred during the second 2 weeks. The results of our study suggest that in the absence of an NFL preseason, injuries are more common during the early regular season, similar to the injury trend noted by Feeley et al.
      • Feeley B.T.
      • Kennelly S.
      • Barnes R.P.
      • et al.
      Epidemiology of National Football League training camp injuries from 1998 to 2007.
      during training camp. However, given the unprecedented nature of the Covid-19 pandemic and its effect on the 2020-2021 NFL season, such a finding should be interpreted with this limitation in mind.
      We speculate that factors similar to those proposed to account for the increased injury rate noted in the early NFL preseason also contributed to the increased injury rate noted in NFL players during weeks 1-4 of the 2020-2021 regular season. These factors include the relative deconditioning and muscle weakness that occurs during the offseason,
      • Orchard J.
      • Marsden J.
      • Lord S.
      • Garlick D.
      Preseason hamstring muscle weakness associated with hamstring muscle injury in Australian footballers.
      ,
      • Croisier J.L.
      • Ganteaume S.
      • Binet J.
      • Genty M.
      • Ferret J.M.
      Strength imbalances and prevention of hamstring injury in professional soccer players: A prospective study.
      as well as fatigue, which suggests that fatigued muscles are more vulnerable to injury.
      • Woods C.
      • Hawkins R.D.
      • Maltby S.
      • et al.
      The Football Association Medical Research Programme:Aan audit of injuries in professional football--analysis of hamstring injuries.
      ,
      • Mair S.D.
      • Seaber A.V.
      • Glisson R.R.
      • Garrett Jr., W.E.
      The role of fatigue in susceptibility to acute muscle strain injury.
      It is likely that the deconditioning of players during the early 2020 NFL regular season was similar to that of past NFL preseasons; however, during the 2020 season players were asked to play for more time and at a higher level than they would typically be expected to play during the early preseason, specifically, starters. Thus, increased time and intensity of play in the context of baseline deconditioning likely explains why the injury rate during the early 2020 NFL season was higher than the injury rate during past NFL preseasons. Our findings contribute to growing body of evidence that fatigue and deconditioning may place athletes at a higher risk for injury.
      Saw et al., in their systematic review of subjective measures used to monitor athletes’ responses to training, noted subjective measures, including mood disturbance, perceived stress and recovery and symptoms of stress, to be highly sensitive to an athlete’s well-being in response to acute and chronic exercise loads.
      • Saw A.E.
      • Main L.C.
      • Gastin P.B.
      Monitoring the athlete training response: Subjective self-reported measures trump commonly used objective measures: A systematic review.
      In light of these findings, the NFL may consider implementing athletes’ self-reported questionnaires in order to monitor athletes’ levels of exhaustion. The benefits of monitoring fatigue and athletes’ well-being include revealing the need for recovery in order to prevent injury, guiding training and competition scheduling, and understanding changes in athletic performance related to fatigue.
      • Mack C.D.
      • Kent R.W.
      • Coughlin M.J.
      • et al.
      Incidence of lower extremity injury in the National Football League: 2015 to 2018.
      ,
      • Halson S.L.
      Monitoring training load to understand fatigue in athletes.
      To our knowledge, no such measures have been practiced in attempt to reduce injury risk in professional football players. Future investigations may be useful in evaluation of these subjective measurement techniques and their efficacy in injury reduction in the NFL.

      Limitations

      This study, as well as other similar publications using the well-established multistep protocol to identify injuries in professional athletes through review of public records, is associated with several limitations. This is a database study, and incomplete data entry and inaccurate reporting of injuries could confound the season-to-season injury differences. Details regarding injury diagnosis and management, including injury severity, exact pathology, imaging reports, and exact medical clearance, were not available for all players. Because injured players were identified using public records, the possibility of reporting errors and omissions exist. We did not assess the rate of injuries over the entire season to see whether the injury rates normalized as the season went on. Our study also lacks objective measures of deconditioning to correlate with injury rates during COVID-19. Finally, there remains the possibility of selection bias in the injured group in which only “newsworthy” players injured were reported on. We attempted to minimize this bias by corroborating reported injuries with 2 additional resources, but the data are limited by what is publicly available.

      Conclusion

      The rate of injury in NFL players during weeks 1-4 of the 2020-2021 regular seasons was significantly higher than that of the 3 recent past NFL preseasons and regular seasons.

      Supplementary Data

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