Why the erg monitor can't tell you about technique
The PM5 measures what reaches the flywheel: split, watts, rate and a force curve. It can't see your body. Two rowers can pull the same split with very different technique, and the one who opens the back early or collapses at the finish is usually the one who stalls or gets hurt as the metres add up.
The erg is also the best place to film technique. The machine doesn't move, the light is steady, and the camera can see everything from feet to handle. That's why every one of the 13 checks can be graded on the erg.
The erg faults it catches, and how
| Fault | What it looks like | What Mocta-X measures |
|---|---|---|
| Shooting the slide | The seat moves back but the handle doesn't; the legs push before the back is connected | Leg–back connection through the drive |
| Opening the back early | Trunk swings before the legs have done their work | Drive sequence: legs → back → arms timing (the heaviest check) |
| Over-reaching or a flat back at the catch | Shins past vertical, or no forward body angle | Shin angle and forward body angle at the catch |
| Too much or too little layback | Collapsing well past the reference, or finishing upright | Layback angle at the finish |
| Rushing the slide | Recovery about as quick as the drive | Slide rhythm: recovery time ÷ drive time, target around 2 |
| Knees up before the hands are away | Handle has to lift over the knees | Recovery sequence: hands → body → knees |
| Bent arms at the catch | Early arm pull that disconnects the legs | Arm extension at the catch |
Here's what that looks like on a real erg stroke. The catch and finish values are the grader's own measurements; this rower's legs weren't fully down at the finish, and it was flagged.
- Forward body angle18.6°
- Shin angle2.9°
- Arm extension159.7°
- Knee compression35.5°
- SequenceIn order
Legs, then back, then arms.
- Layback36.6°
- Leg extension151.3° (outside target)
- Trunk swing55.2°
Outside target on this stroke
- SequenceIn order
Hands, then body, then knees.
Each check has a reference range, and each stroke is scored on how far outside it you fell. The AI coach then picks the fault costing you most and links to the stroke where it shows most clearly. The rowing technique guide covers each check in more detail, and common rowing mistakes gives the drill for each fault.
Setting up the camera on the erg
- Put the phone level with your hip, square to the side of the erg. A chair or a second erg works as a stand.
- Step back until the whole slide, from the front of the rail to the back, is in frame with your hands at full reach.
- Film in landscape, with the window or bright light behind the camera rather than behind you.
- Row at your normal rate for at least five or six unbroken strokes. A full piece is better, because durability is measured across it.
- Upload the clip, or record it straight into the iPhone app's capture wizard.
The full checklist, including what to do on a crowded erg floor, is in how to film rowing.
Technique next to your numbers
On iPhone, Mocta-X for iPhone connects to a Concept2 PM5 over Bluetooth and keeps recording with the screen locked. It syncs your Concept2 Logbook and tracks personal bests at 4,000 m, 8,000 m, 10,000 m and 30 minutes. On Elite, a live voice coach reads your split, rate, heart rate and target while you row.
That puts the question most rowers actually have in one place: my split dropped at 1,500 m, so what happened to my technique at the same point? The durability score shows the stroke where your shape broke.
Graded against the right reference
Reference ranges come from published sources: Kleshnev's BioRow data (including measurements from the 2023 World Championships), Egan-Shuttler et al. (2013), and Concept2 and British Rowing technique guidance. You choose a style (Recreational/Fitness, Competitive/Sprint, Masters/Long-distance, or Technical/Coaching), and the targets and strictness change to match. All weights are in the scoring guide.
Questions
Where should I put my phone to film the erg?
Side-on, square to the erg, at about hip height, far enough back that the whole slide and your hands at full reach are in frame. Keep bright windows behind the camera, not behind you.
Does it work with a Concept2 RowErg?
Yes. The video analysis works with any erg filmed side-on. The iPhone app also connects to a Concept2 PM5 over Bluetooth and syncs your Concept2 Logbook.
What is shooting the slide?
The seat moves toward the bow before the handle does, because the legs push before the back and arms are connected to the handle. Mocta-X grades this as leg–back connection on every stroke.
How many strokes do I need to film?
At least five or six unbroken strokes for a score. A longer piece is better, because the performance score measures how your technique holds up over time.
Can it tell me my ideal layback?
It grades layback against a reference range for the style you select, so a Competitive/Sprint target differs from Recreational/Fitness. The scoring guide lists how much each check weighs.