Executive Summary

Mack et al. (2019) examined lower extremity injury rates among NFL players on synthetic turf vs. natural grass over a ten-season period using data from the NFL Injury Surveillance System. The study found that non-contact lower extremity injuries — including ACL tears, ankle sprains, and knee injuries — occurred at higher rates on synthetic turf than on natural grass across the study population.

The study is one of the most comprehensive analyses of NFL injury data by surface type available in peer-reviewed literature. Its findings carry significant weight in synthetic turf specification discussions at the professional and high-performance amateur level — and are frequently cited by both critics and proponents of synthetic turf in ways that oversimplify what the data actually shows.

Architects and specifiers designing fields for high-performance athletic use should understand the study’s findings, its methodological strengths, and its limitations before applying its conclusions to specification decisions.

Key Findings

Higher Non-Contact Lower Extremity Injury Rates on Synthetic Turf

NFL players experienced statistically higher rates of non-contact lower extremity injuries on synthetic turf compared to natural grass across the ten-season study period. This finding was consistent across multiple injury types and multiple seasons.

ACL and Ankle Injuries Most Pronounced

ACL tears and ankle sprains showed the most pronounced surface-related differences. These injury types are biomechanically consistent with elevated rotational resistance, the primary surface-shoe interaction variable proposed as the mechanism behind the findings.

Non-Contact Injuries Specifically

The study focused on non-contact injuries, those occurring without direct player-to-player contact. This distinction is important because non-contact injuries are more likely to reflect surface-athlete interaction than contact injuries, which are influenced primarily by the collision itself.

Consistent Across Positions

The surface-related injury rate difference was observed across multiple player positions, not limited to positions with specific movement patterns. This consistency across positions strengthens the generalizability of the finding within the NFL population.

Data Source, NFL Injury Surveillance System

The study used data from the NFL Injury Surveillance System, one of the most comprehensive professional athlete injury datasets available. Ten seasons of data across all NFL teams provides a large, statistically robust sample for surface-type comparison.

Important Limitations

Surface Characterization – No Independent Testing

As with most epidemiological injury studies, fields were categorized as synthetic turf or natural grass based on reported surface type, not independent performance testing. Synthetic turf fields in the NFL vary significantly in age, infill type, maintenance condition, and rotational resistance values. The study cannot differentiate between well-maintained synthetic turf systems within acceptable rotational resistance thresholds and aging or poorly maintained systems with elevated values.

Footwear Not Controlled

The study did not control for footwear type across players or surfaces. NFL players use a range of cleat configurations that interact differently with synthetic turf and natural grass surfaces. Cleat-surface interaction is a primary determinant of rotational resistance at the player level — and this variable is not captured in the study design.

Natural Grass Variability

Natural grass fields also vary significantly in condition, firmness, and surface characteristics, particularly late in the season when field condition deteriorates. The study treats natural grass as a homogeneous comparison category, which may not reflect the actual variability in natural grass surface performance across NFL stadiums and seasons.

Causation vs. Correlation

The study establishes a statistical association between synthetic turf and higher non-contact lower extremity injury rates, not a causal mechanism. The proposed mechanism, surface-shoe interaction and rotational resistance, is biomechanically plausible but not directly tested in this study design.

NFL Population Specificity

Findings apply to NFL players, elite professional athletes with specific physical profiles, training loads, and competitive schedules. Extrapolating these findings to collegiate, high school, or recreational athletes requires additional evidence.

Why This Matters

For Architects and Specifiers

Mack et al. 2019 is one of the most cited studies in high-performance synthetic turf specification discussions. Architects and specifiers designing fields for elite or high-performance athletic use, NCAA Division I, professional training facilities, high-use municipal fields, should be familiar with its findings and limitations.

The actionable implication for specification is consistent with Howard et al. 2020, specify rotational resistance thresholds, require independent lifecycle testing, and select infill systems with documented performance appropriate for the anticipated athlete population and use intensity.

For NFL and Professional Venue Operators

The NFL has responded to this and related research by implementing enhanced field testing protocols and publishing field performance data through the NFLPA. Field operators at the professional level should be aware that surface performance monitoring, particularly rotational resistance, is now an expected component of responsible field management at the highest levels of the sport.

For High-Performance Amateur Facilities

NCAA Division I programs, high-use municipal fields, and facilities serving elite youth and amateur athletes operate at use intensities and athletic performance levels closer to the NFL than to recreational use. The findings of Mack et al. 2019 are relevant to specification and maintenance decisions at these facilities particularly for fields used heavily for soccer, football, and other sports with high rotational demand.

For the Industry

Mack et al. 2019 reinforces the case for surface-specific performance standards in injury surveillance research. A finding that non-contact injury rates are higher on “synthetic turf” as a category tells us less than a finding that rates are higher on synthetic turf fields with specific rotational resistance characteristics. Better surface characterization in future research would produce more actionable findings for the field specification community.

Act Global Perspective

Mack et al. 2019 reinforces the same principle as Howard et al. 2020, rotational resistance management is the central synthetic turf safety variable for lower extremity injury risk, and it requires active lifecycle management, not just installation compliance.

Act Global’s response to this body of research is reflected in our system engineering approach. Every Act Global sports turf system is specified with rotational resistance as a primary design target. Infill type, infill depth, fiber density, and backing system are selected in combination to achieve and maintain rotational resistance values within the FIFA Quality range of 25–50 Nm throughout the field’s service life.

For architects and specifiers designing high-performance athletic facilities, NFL training venues, NCAA Division I fields, or high-use municipal fields serving elite athletes, Act Global recommends:

Specifying rotational resistance thresholds in procurement documents, FIFA Quality range of 25–50 Nm as a minimum standard
Requiring independent rotational resistance testing at installation from an ISO 17025-accredited laboratory
Requiring zone-by-zone rotational resistance measurement, not just a field average, to identify high-resistance areas in goal mouths, hash marks, and high-traffic zones
Including lifecycle rotational resistance monitoring in field maintenance contracts with defined intervention thresholds
Selecting infill systems with documented rotational resistance performance appropriate for the athlete population and use intensity

The findings of Mack et al. 2019 do not argue against synthetic turf, they argue for better-specified, better-maintained synthetic turf with independently verified rotational resistance performance throughout the field’s service life.

Related Resources

Access the Original Study

Citation

Mack, C.D., Kent, R., Coughlin, M., Shirasawa, H., Zimmermann, W., Viano, D.C., & Talavage, T.M. (2019). Incidence of lower extremity injury in the National Football League: 2015 to 2018. American Journal of Sports Medicine, 47(12), 2877–2885.

Access

The full study is available through PubMed and the American Journal of Sports Medicine. Act Global does not host or reproduce the full text of this or any third-party publication.

Editorial Note

This review reflects Act Global’s interpretation of a publicly available peer-reviewed study. It is provided for educational purposes only and does not constitute medical, legal, or engineering advice. Act Global makes no claim to academic authorship of this research. Refer to the original publication for complete methodology, data, and findings.

NFL Lower Extremity Injury Rates on Synthetic Turf vs. Natural Grass – Review of Mack et al. 2019