Why I Don’t Use Motion Capture in Bike Fitting

As a sport scientist, my main areas of interest are biomechanics and performance.

The scientist in me likes data. But data only matters if it is meaningful, relevant and grounded in evidence.

Capturing data alone is not science. More data does not automatically lead to better insight.

Without context, data often becomes noise rather than signal.

And when scientifically minded people are given numbers that look precise, it can create a false sense of confidence. When that happens, riders are often convinced by the same illusion.

To be clear, I am not anti technology and I am not anti motion capture. Technology absolutely has a place in bike fitting.

But it should never be the centre of the process.

The Early Promise of Motion Capture

When Retül first appeared it created a lot of curiosity in the bike fitting world.

For the first time you could measure rider joint angles in real time and generate more data than previous fitting systems allowed. At the time it felt revolutionary.

But the scientist in me kept asking a simple question.

More advanced than what?

Being more advanced than previous tools does not automatically make something better or more meaningful.

If you step back and look at it objectively, motion capture systems place markers on the rider and generate a two dimensional stick figure model of the body.

The technology itself is clever.

But clever does not always mean useful.

My Own Experience with Motion Capture

In 2016 I invested in the STT motion capture system.

It used more markers, provided more analysis tools and produced even more data than the systems that came before it. Like most people in the industry, I was curious to see what it could add to the fitting process.

Looking back, the marketing had clearly done its job. Even when you try to approach things critically, it is easy to be pulled in by the promise of more precision and better insights.

But eventually the important question has to be asked.

Is this a tool or a gadget?

A true tool improves outcomes by increasing repeatability, reliability, accuracy and efficiency.

In practice, motion capture did none of these.

Instead I found that it slowed the process down, added unnecessary complexity and increased the cost of the fitting without improving the outcome for the rider.

It can be a useful educational tool to demonstrate general movement trends, but it is not diagnostic.

What the Evidence Actually Shows

The marketing around motion capture systems often focuses on precision. These systems can measure marker positions to the millimetre.

Technically that statement is correct.

The problem is that the largest source of error is not the system itself. It is the placement of the markers.

Research consistently shows that both inter tester and intra tester marker placement variability can range between 8 millimetres and 25 millimetres.

Think about that for a moment.

Many bike fit adjustments such as saddle height, cleat position or bar changes are often smaller than this range.

That means the measurement error can be larger than the adjustment you are trying to make.

When that happens, claims of precision and repeatability start to fall apart.

The system may measure the marker precisely, but if the marker itself is placed differently each time then the output becomes unreliable.

That is not evidence based precision.

It is simply confidence placed in numbers that look scientific.

What Actually Matters in Bike Fitting

Bike fitting is not solved by measuring more angles.

It is solved by understanding how a rider interacts with the bike.

This includes load distribution, joint capacity, movement strategy, rider goals and the way equipment interacts with the body.

Biomechanics should always come before numbers.

Technology should support decision making rather than replace it.

In practice, the most powerful tools in bike fitting are still experience, observation, pressure mapping, rider feedback and sound biomechanical reasoning.

Motion capture can be interesting.

But interesting is not the same as useful.

And useful is what actually improves riders.