ARC study: ACL injuries in women's football
Research proposal · October 2026
ARC (ACL Risk in Competition) studies how player biomechanics change before an ACL injury.
Research goal
Primary
To find out whether measurable biomechanical changes appear in a player's match movement before an ACL injury. If they do, the study will show when they appear and what they look like.
Secondary
To find out whether players who return to play after an ACL injury get back to their own pre-injury baseline, or settle at a new one.
A clear null result is a finding in its own right. If no biomechanical markers appear before an ACL injury, the study will report that.
Approach
The study repeats the design of PRISM, FitWise's study of hamstring injuries in Premier League players.
The study is retrospective and runs on historical data: match footage from past WSL seasons, in which the injuries have already happened. Nothing new is recorded, and players do not need to take part.
Cohort
- Injured group: WSL players with an ACL injury.
- Comparison group: players with no injury, matched by position.
From broadcast to 3D
Each player is reconstructed in 3D from the match broadcast, frame by frame, with no sensors or markers. Below is one stride of a sprint: the broadcast frame at each phase, and the 3D body rebuilt from it.
Metrics
We measure in-game sprints. In each step, we detect five kinogram phases: toe-off, MVP (maximal vertical projection), late swing, touchdown and mid-stance. At each phase, we compute 30+ joint angles.
Each player is compared against her own healthy baseline.
Stages
1. Dataset
We identify the injured players and the comparison group. For each injury, we select at least four matches before it and at least one match after it.
2. Processing
FitWise processes the footage into 3D movement data and extracts every high-speed run and sprint. Each run is checked for whether the camera view supports reliable measurement.
3. Data analysis
The measures and the analysis plan are fixed before anyone looks at the injured players. We establish trends first and then test the link to injury, holding regular update calls with WSL throughout.
4. Publication
We publish the results whether they are positive or negative, and WSL is invited to co-author. WSL brings the findings to clubs and practitioner groups.
Roles
Party
Role
WSL Football
Provides the footage and takes part in regular research discussions.
Ian Varley, Robin Thorpe
Lead and guide the study design and the analysis.
FitWise
Designs the study, processes the footage, and runs the analysis.
The study uses existing broadcast footage and collects no new data from players.
Footage requirements
Footage quality is the main limit on what the study can measure.
Parameter
Minimum
Preferred
Resolution of the wide view
1080p (1920 × 1080)
4K (3840 × 2160) where it exists
Cameras
One: the main broadcast camera
Several angles of the same match (main, tactical, behind-goal)
Frame rate
25 frames per second
50 frames per second, progressive
Source and compression
Files as delivered by the broadcaster or Opta. YouTube re-encodes its uploads, which removes fine detail at the joints even at 1080p.
The highest-bitrate master that exists
Coverage
Full match from the wide camera. We will automatically remove cuts to close-ups and replays.
The uninterrupted wide feed (clean or tactical feed)
Multiple cameras
FitWise supports multiple cameras. Footage from several cameras at the same match is merged into one 3D reconstruction of each player. A player hidden from one camera is still tracked from another, and a run that heads straight at one camera is seen side-on by a second. One camera is enough to run the study, but additional angles improve what we can measure.
Why we do this
Our goal is to reduce injuries.
ARC asks whether the ACL injuries show specific movement signatures in the matches before they happen. If they do, staff can spot the change early and act on it: adjust her training or game load, add targeted strength work, or take a closer look.
The goal of our research programme is to create practical and science-based methods to reduce the number of soft tissue injuries in the elite sport.