Executive Summary
Howard et al. (2020) examined ACL injury rates among NCAA soccer players competing on synthetic turf vs. natural grass over a multi-season period. The study found that female soccer players experienced statistically higher rates of ACL injuries on synthetic turf compared to natural grass. No statistically significant difference was found for male soccer players.
The study is one of the most frequently cited pieces of research in synthetic turf safety discussions, and one of the most frequently misrepresented. Its findings are specific to NCAA soccer, specific to female athletes, and specific to the surface types and footwear combinations present in the study population. Architects and specifiers should understand both what the study shows and what it does not show before applying its conclusions to field specification decisions.
Key Findings
Female Soccer Players – Statistically Significant Difference
Female NCAA soccer players experienced ACL injury rates approximately 1.5 times higher on synthetic turf than on natural grass. This difference was statistically significant, meaning it is unlikely to be explained by chance variation in the data.
Male Soccer Players – No Statistically Significant Difference
Male NCAA soccer players did not show a statistically significant difference in ACL injury rates between synthetic turf and natural grass. The difference observed was within the range explainable by normal data variation.
ACL Injuries Specifically – Not All Injuries
The study examined ACL injuries specifically, not total injury rates, not all lower-extremity injuries, and not injuries across all sports. Conclusions from this study apply to ACL injury risk in soccer specifically and should not be generalized to overall injury rates or other sports without additional evidence.
Surface-Shoe Interaction as the Proposed Mechanism
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Data Source – NCAA Injury Surveillance Program
The study drew on data from the NCAA Injury Surveillance Program – a large, multi-institution dataset covering competitive play and practice across multiple seasons. The dataset is considered one of the most rigorous sources of collegiate athlete injury data available.
Important Limitations
Surface Characterization – No Independent Testing
The study categorized fields as “synthetic turf” or “natural grass” based on reported surface type, not independent performance testing. Synthetic turf fields in the study varied in age, infill type, infill depth, maintenance condition, and rotational resistance values. A field labeled “synthetic turf” in the dataset could range from a well-maintained, recently installed system within FIFA rotational resistance thresholds to an aging, poorly maintained field with significantly elevated rotational resistance. This heterogeneity limits the ability to draw conclusions about specific synthetic turf system types.
Footwear Not Controlled
The study did not control for footwear type across athletes or surfaces. Cleat configuration significantly affects rotational resistance — and therefore ACL injury risk — independent of surface type. The interaction between specific cleat configurations and specific synthetic turf systems is a critical variable not captured in the study design.
Causation vs. Correlation
The study establishes a statistical association between synthetic turf and higher ACL injury rates in female NCAA soccer players, not a causal mechanism. While the authors propose surface-shoe interaction as the likely mechanism, the study design does not permit causal conclusions.
NCAA Population Specificity
Findings apply to NCAA-level female soccer players, a specific population with specific training loads, competitive schedules, biomechanical profiles, and footwear choices. Extrapolating these findings to youth players, recreational athletes, male soccer players, or athletes in other sports requires additional evidence.
No Infill-Specific Analysis
The study does not differentiate between synthetic turf systems by infill type. Crumb rubber, sand, organic, and TPE infill systems have meaningfully different rotational resistance profiles, and therefore potentially different ACL injury risk implications. The study’s findings cannot be applied equally to all infill types.
Why This Matters
For Architects and Specifiers
Howard et al. 2020 is frequently cited in synthetic turf procurement discussions, often without the limitations context that makes the findings actionable. Architects and specifiers who understand both the findings and their limitations are better positioned to make defensible specification decisions and to respond to stakeholder concerns about synthetic turf safety with accuracy rather than generalization.
The practical implication for specification is not “avoid synthetic turf for female soccer” it is “specify synthetic turf systems with independently verified rotational resistance within FIFA thresholds and require lifecycle maintenance that keeps rotational resistance within those thresholds throughout the field’s service life.”
For Field Owners and Facility Managers
The study’s proposed mechanism, elevated rotational resistance, is a manageable variable. Rotational resistance is measurable, independently testable, and directly influenced by infill selection, infill depth maintenance, and surface condition. A field owner who monitors rotational resistance annually and maintains infill depth within specification is actively managing the primary risk factor identified in this research.
For School Districts and Municipalities
School districts and municipalities specifying fields for female soccer programs should include rotational resistance thresholds in their procurement specifications, at minimum the FIFA Quality range of 25–50 Nm, and require independent lifecycle testing to verify that those thresholds are maintained over the field’s service life. This is the actionable response to Howard et al. 2020 for public procurement.
For the Industry
Howard et al. 2020 reinforces the case for standardized, independent surface testing, not just at installation but throughout the field lifecycle. A finding that ACL injury rates are higher on “synthetic turf” as a category is less useful than a finding that ACL injury rates are higher on synthetic turf fields with rotational resistance above X Nm. Getting to that level of specificity requires better surface characterization data than currently exists in most injury surveillance datasets.
Act Global Perspective
Howard et al. 2020 confirms what Act Global’s system engineering approach has always prioritized, rotational resistance is not a compliance checkbox, it is a lifecycle safety variable that requires active management throughout a field’s service life.
The study’s proposed mechanism, surface-shoe interaction and elevated rotational resistance as the primary driver of ACL injury risk in female soccer players, is directly addressable through system specification and maintenance. Act Global specifies rotational resistance as a system-level design target across all sports turf systems. Fiber density, infill type, infill depth, 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, not just at installation.
Every Act Global sports turf system includes published rotational resistance data from ISO 17025-accredited independent laboratories, Firefly Sports Testing, Labosport, and Sports Labs. Maintenance guidelines include infill depth monitoring and decompaction schedules specifically designed to prevent rotational resistance from rising above acceptable thresholds as infill compacts under use.
For architects and specifiers designing fields for female soccer programs, Act Global recommends:
- Specifying rotational resistance thresholds in procurement documents, minimum FIFA Quality range of 25–50 Nm
- Requiring independent rotational resistance testing at installation from an ISO 17025-accredited laboratory
- Including lifecycle rotational resistance monitoring in field maintenance contracts
- Selecting infill systems with documented rotational resistance performance appropriate for the anticipated use intensity and athlete population
The question Howard et al. 2020 raises is not whether to specify synthetic turf, it is how to specify and maintain synthetic turf systems that keep rotational resistance within safe ranges for female soccer athletes throughout the field’s full service life.
Related Resources
Access the Original Study
Citation
Howard, E., Friesen, K., Patel, P., Rosenbaum, D., & Bhatt, D. (2020). Anterior cruciate ligament injury rates on artificial turf versus natural grass: A systematic review. Journal of Athletic Training, 55(7), 681–687.
Access
The full study is available through the National Institutes of Health PubMed database and the Journal of Athletic Training. 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.
