About Runlens
Built by a runner,
for runners.
A simple tool that helps you see what's going on with your running form — no wearables or lab required.
The Story
What is Runlens?
Upload a short video from the side, and you get back clear metrics and visual feedback — cadence, vertical bounce, knee angle, and more. I built it because I wanted to learn how I could improve my form using a lens (get it?) outside of the numbers on my Apple Watch and iPhone.
The Analysis
How the analysis works
Runlens uses computer vision to track your joints frame by frame, then measures things like cadence, vertical bounce, and stride length against research-backed targets. The pipeline combines MediaPipe Pose for body tracking with rule-based heuristics tuned for running — so you get numbers and flags that are easy to act on.
Please be aware that results might vary from what you get on your wearables or fitness trackers; these devices use onboard accelerometers to analyze your motion; Runlens uses computer vision and the accuracy will be affected by things like motion blur, poor lighting and other environmental factors. As such, our results are best used as directional insights and trends, not clinical measurements.
One final note: a running coach told me that if her runners don't have any issues with pain or injury while running, then she doesn't bother to correct their form. Human bodies are all different and they work the way they work, so if that's you, then you might not need Runlens. But, if you're curious about your form, and want some quick insights, then Runlens might be the tool you're looking for. Either way, happy running! 🏃
Best Results
Tips for accurate analysis
Computer vision is sensitive to how the video is recorded. These tips make a big difference.
Shoot from the side
Place your camera at a strict 90° angle to your direction of travel. Even a slight diagonal angle throws off joint angle and stride calculations.
Use 60 fps or higher
Higher frame rates reduce motion blur and give the pose tracker more frames to work with. 30 fps is the minimum; 60 fps or 120 fps produces noticeably better results.
Keep the camera level and still
Mount it on a tripod or prop it against something stable. A shaky or panning camera makes landmark tracking unreliable.
Frame your whole body
Leave a little headroom above and show your feet clearly. Cropping out your head or feet causes the pose model to guess those joints, reducing accuracy.
Film in good, even light
Outdoor daylight is ideal. Avoid filming with the sun or a bright window directly behind you — backlighting washes out your silhouette and hurts detection.
Wear fitted clothing
Loose or baggy clothes obscure joint positions. Fitted running kit gives the pose model a much clearer view of your hips, knees, and ankles.
Keep clips short
10–30 seconds (covering several full stride cycles) is the sweet spot. Longer clips take more time to process and don't meaningfully improve the results.
Simple backgrounds help
A plain wall, road, or open field behind you makes it easier to isolate your body. Busy or high-contrast backgrounds (crowds, fences, foliage) can confuse the tracker.
The Numbers
Metrics explained
| Metric | Target | What it means |
|---|---|---|
| Cadence | 170–180 spm | Steps per minute |
| Vertical oscill. | < 10 cm | How much you bounce |
| Knee flexion | > 15° | Shock absorption at impact |
| Trunk lean | < 15° | Forward body angle |
| Overstriding | < 10 cm ahead | Foot landing vs. hips |
Important
What Runlens is not
Runlens is a fitness tool, not a medical device. It can't diagnose injuries or replace a physio or running coach. Think of it as a second pair of eyes on your form — the kind you'd get from a knowledgeable friend.