Does the Environment Influence the Frequency of Concussion Incidence in Professional Football?

Abstract

Background Sports-related concussion is a major cause of mild traumatic brain injury (mTBI). It is possible that environmental factors, such as temperature, humidity, and stadium's altitude, may influence the overall incidence of concussions during a game. Purpose To examine the impact of environmental factors, such as temperature, humidity, barometric pressure, and dew point, on concussion incidence. Methods Public Broadcasting Service (PBS) FRONTLINE Concussion Watch was used to collect injury data on 32 NFL teams during regular season games from 2012 to 2015. Weather data points were collected from Weather Underground. Concussion incidence per game, the probability of a concussion during a game, and a difference in mean game-day temperature, humidity, dew point, and barometric pressure between concussion and concussion-free games were calculated. Our analysis included t-tests, analysis of variance (ANOVA), multivariate correlation tests, and logistic and Poisson regression. Results Overall, 564 concussions were reported. There were 411 games with concussions and 549 games without concussions. We observed a significant decrease in concussion incidence with increasing temperature, both when the temperature was divided into 20^oF increments or into quartiles (p = 0.005 and p = 0.002, respectively). We identified a statistically significant lower mean-game day temperature in concussion games compared to concussion-free games (p < 0.0006). We also observed a significant decrease in the incidence of concussion per game with increasing dew point. There was no significant difference in concussion incidence in barometric pressure and humidity. The logistic regression model predicted a decrease in the probability of a concussion in games with higher temperatures and dew points. Conclusions National Football League (NFL) players experienced an increased risk of concussion during football games played in colder temperatures and at lower dew points. Further research on environmental effects on concussions may aid in improving player safety in football leagues.

Keywords: american football; concussion; environmental factors; epidemiology; temperature.

Figure 1. Concussion Incidence Increases as Game Temperature Decreases

(a) Bar graph shows mean temperature (SEM) for concussion and concussion-free games (p <0.001, ***). (b-c) Bar graphs show mean concussion incidence for games played at different temperature increments. Graph b divides temperature into 20^oF increments, and graph c divides temperature into 15^oF and 30^oF increments. (d) Poisson regression computes the predicted concussion incidence of any given game played at a certain temperature. The environmental factors of temperature, dew point, humidity, and barometric pressure were utilized in the model.

Figure 2. Lower Temperature and Dew Point Is Predictive of Concussion Incidence

(a-d) Logistic regression, taking into account all four environmental factors, was performed on the total 960 games to compute the predicted probability that a concussion would occur during a game. Graphs a, b, c, and d show temperature, dew point, humidity, and barometric pressure, respectively.

Figure 3. Concussion Incidence Increases as Dew Point Decreases

(a) Bar graph shows mean dew point (SEM) for concussion and concussion-free games (p<0.01, **). (b) Bar graph shows mean concussion incidence for games played at different dew point increments. (c) Poisson regression computes the predicted concussion incidence of any given game played at a certain dew point. The environmental factors of temperature, dew point, humidity, and barometric pressure were utilized in the model.

Figure 4. Humidity and Barometric Pressure Do Not Affect Concussion Incidence

(a) Bar graph shows mean dew point (SEM) for concussion and concussion-free games (p>0.05, NS). (b) Poisson regression computes the predicted concussion incidence of any given game played at a certain humidity. The environmental factors of temperature, dew point, humidity, and barometric pressure were utilized in the model. (c) Bar graph shows mean barometric pressure (SEM) for concussion and concussion-free games (p>0.05, NS). (d) Poisson regression computes the predicted concussion incidence of any given game played at a certain barometric pressure. The environmental factors of temperature, dew point, humidity, and barometric pressure were utilized in the model.