About AxyZ

The Problem: Why Bike Fit Is Broken

Bike fit is the #1 cause of cycling knee pain. A saddle positioned just 1cm too low or too high creates biomechanical stress that accumulates over weeks of riding—anterior knee pain, IT band pain, or lower back strain.

Most cyclists respond by doing what they can: adjusting the saddle and hoping it helps, reading conflicting advice from forums, or waiting it out. Some book a professional fit ($150–$400, 2–3 hours, travel required). For many, that isn't realistic. Rural location, tight budget, or just a quick question that doesn't justify the cost. So they guess. And many keep guessing for months.

The irony: the measurements that matter most in bike fitting are measurable, standardized, and reliable. Saddle height, hip angle, torso lean, pedaling stability—these are the variables that cause 80% of common fit problems. They can be measured from a phone video using the same computer vision technology used in professional sports analysis. The only thing missing was the tool.

Why I Built AxyZ

I'm Aaron Gehrke. I've been riding bikes for twenty years—mountain trails, gravel roads, and for the past few years, indoor trainers. I'm not a professional fitter or a biomechanist. I'm a builder who got frustrated.

I spent months guessing at my own fit. Saddle too low = anterior knee pain. Saddle too high = IT band flare. I read one source saying "saddle height should be 109% of inseam," another saying "look for 35 degrees of knee flexion." Nobody agreed. I knew a pro fit was the right answer, but I couldn't book one every time I dropped a few pounds or swapped a component.

So in late 2024, I started building. If the science is settled and the measurements are standardized, why can't a computer do this part?

I spent months learning how professional fitters measure (motion capture, video analysis, benchmarks like Holmes et al. 1994), what makes a measurement reliable (multi-frame averaging, device-agnostic angle extraction), and where computer vision fails (you can't measure lateral knee tracking from a side view—you need 3D capture). The result is AxyZ: a tool that measures the four most impactful fit variables from a 10-second video, instantly, free.

What AxyZ Does (and Doesn't)

AxyZ measures:

• • Saddle height (knee angle at bottom dead center)—the single most common cause of cycling knee pain
• • Hip angle (hip flexion at top dead center)—flags hip flexor compression
• • Torso lean (upper body angle by bike type)—scored against discipline-appropriate norms
• • Pedaling stability (hip drop variance)—the signature of a saddle set too high

AxyZ cannot measure:

• • Lateral knee tracking (cleat alignment, foot mechanics)—requires 3D multi-camera capture
• • Handlebar reach, saddle fore-aft position, or hand pressure—requires in-person assessment
• • Flexibility, range of motion, or physical asymmetries—requires a person

This is by design. AxyZ is the 80/20 tool: it solves the most common problems in 2 minutes. It's not a replacement for a professional fit. It's the answer to "something doesn't feel right and I need a clue" at 11 PM on a Tuesday.

How This Was Validated

AxyZ uses Google MediaPipe Pose, a computer vision model that detects 33 body landmarks in real time—the same technology used in professional sports analysis, physical therapy apps, and motion capture research. It has been validated in academic literature on pose estimation accuracy.

For the bike-fitting benchmarks, AxyZ references:

• • Holmes et al. (1994): "Lower extremity overuse in cyclists"—establishes the 35–40° knee flexion target at bottom dead center
• • BikeDynamics and BikeFitAdviser standard fitting protocols—industry-standard measurements
• • Retül and Specialized BG Fit benchmarks—what professional fitters use as their reference standards

The limitations are transparent: side-view pose estimation is reliable for joint angles in the sagittal plane (forward/backward), but cannot measure lateral (side-to-side) or rotational variables. Accuracy depends on a level, perpendicular camera view and sufficient lighting. A 10-second video averaged across multiple pedal cycles is more reliable than any single frame.

Why This Is a Side Project

AxyZ is my side project, not my full-time job. I'm not venture-backed. There's no Series A pressure to claim medical expertise I don't have or oversell the tool's capabilities. That's intentional.

The goal is simple: give cyclists a practical, honest, free starting point for understanding their fit. Some will use it and feel better immediately. Some will discover they need a professional fit and have better information when they book one. Both outcomes are wins.