How it works
Everything rowergt reports comes from twelve body points in a side-on video. This page says which points, which angles, and exactly what makes a stroke get flagged.
From video to body points
The clip is stepped through in your browser at 20 frames a second. A pose model (MoveNet Lightning, running in the tab) finds shoulders, elbows, wrists, hips, knees and ankles in each frame. Face points are dropped the moment they are found. The video is never uploaded; only the measurements below are kept.
The side of the body nearer the camera is used — the one the model sees better over the whole clip. The rower faces the foot stretcher, and that direction sets the sign of every angle, so a clip filmed from either side reads the same.
The four angles
| Angle | Points | What it shows |
|---|---|---|
| Knee | hip – knee – ankle | Leg drive. Small at the catch, close to 180° when the legs are flat. |
| Trunk | shoulder – hip, against the horizontal | Back swing. 90° is upright; less is leaning towards the feet, more is lying back. |
| Elbow | shoulder – elbow – wrist | Arm pull. Long arms near 180°, bent at the finish. |
| Shin | knee – ankle, against the vertical | Compression at the catch. 0° is vertical; positive is short of it, negative past it. |
Finding strokes
The wrist stands in for the handle. Its distance from the ankle along the slide is smallest at the catch and largest at the finish. A stroke runs from one catch to the next; the drive is catch to finish, the recovery finish to the next catch. Stroke rate is 60 divided by the stroke's length in seconds, and the ratio is recovery time over drive time. Strokes with a gap in the video, or slower than 12 or faster than 50 strokes a minute, are left out rather than guessed.
Sequencing
Over each drive, every segment's progress goes from 0% (where it was at the catch) to 100% (where it ended at the finish). A segment has startedat 20% and is done at 80%. The timeline on each piece is the median of these curves across its strokes. On the recovery the same is done in reverse: arms, then back, then legs.
Every fault, and what triggers it
These thresholds are rowergt's defaults. They are written down so a coach can disagree with a specific number — tell us through the feedback link if one is wrong for your athletes.
| Fault | When | Flagged when |
|---|---|---|
| Back opens early | Drive | The trunk had swung 30% of its way back before the legs were half way down. |
| Arms bend early | Drive | The elbows had done 30% of their bend before the legs were 70% down. |
| Seat shoots | Drive | The trunk fell forward by more than 6° in the first part of the drive — the seat moved and the shoulders did not follow. |
| Knees rise before the hands are past them | Recovery | The knees had come 25% of their way up before the arms were 90% straight. |
| Over-compressed at the catch | Catch | Shin more than 10° past vertical at the catch. |
| Short at the catch | Catch | Shin more than 20° short of vertical at the catch. |
| Arms bent at the catch | Catch | Elbow under 155° at the catch. |
| No forward body angle at the catch | Catch | Trunk less than 10° forward of vertical at the catch. |
| Legs not flat at the finish | Finish | Knee under 155° at the finish. |
| Finishes in front of vertical | Finish | Trunk still forward of vertical at the finish. |
| Lying back too far | Finish | Trunk more than 35° past vertical at the finish. |
| Hands do not reach the body | Finish | Elbow still over 120° at the finish. |
What it cannot see
- Force, power or split — only angles and timing. Use the monitor for those.
- The shape of the spine. Shoulder and hip give one line, so a rounded back and a straight one at the same angle look alike.
- The far side of the body, and anything hidden behind the erg or another rower.
- Hands and feet beyond the wrist and ankle — the wrist stands in for the handle.
A camera that is not side-on changes every angle. If the result looks wrong, check the filming first: square to the erg, level with the seat, the whole body in frame.