Knee track

Understanding and interpreting knee track visualization in Velogic Studio for better bike fitting

As a fitter, it's useful to know what your rider's knee is doing during the pedal stroke. For example, is the knee moving directly up & down, or is it flaring out (away from the frame) at the top of the stroke, possibly indicating hip impingement? Is the "up" stroke different from the "down" stroke, possibly indicating pelvic twisting?

Some bike fit systems attempt to visualise this with a frontal camera and lasers; and you can certainly use a frontal webcam and laser with Velogic Studio.

However, Velogic Studio has an even better way to visualize and quantify knee movement, made possible because our lateral camera can see depth. This means that Velogic Studio can see the knee moving away from the camera & towards the frame (and vice-versa) during the stroke.

Knee track visualization

Knee track visualization showing green and blue lines representing downward and upward knee movement paths

The knee track is collected automatically when you capture a position. The components of the knee track visualization are:

• An illustration of of a rider. This will appear on either the right-hand side or left-hand side of the image, depending on whether the capture was of the right side of the rider or the left.

• Green and blue lines representing the path of the knee as it travels down and up the pedal stroke.

This single image captures the path of the knee all the way through the pedal stroke. It may help to imagine a small light mounted on the side of the rider's knee, and a long-exposure camera. You can imagine the light being green when the rider's knee is moving down, and blue when the rider's knee is moving back up. If you could capture the path of that light, averaged over many pedal strokes, you will have a good mental image of what the knee track image is showing.

Interpreting the knee track visualization

Velogic Studio provides you with a lot of data so that you can make judgements across a range of factors. You shouldn't try to diagnose issues solely from the knee track; however, there are some characteristic "patterns" that might help indicate particular problems.

Angled knee track

This may indicate that the seat is too low, forcing the knee to move outwards when it is flexed.

Angled knee track pattern indicating potentially low seat height forcing outward knee movement

Separated knee track

If the down stroke and up stroke are very separated, with the down stroke is much closer to the frame, this may indicate that the rider is twisting their pelvis e.g. to accommodate the seat being too high.

Separated knee track showing distinct downstroke and upstroke paths indicating possible pelvic twisting

Mostly vertical & close together

A knee track where the lines are mostly close together and close to vertical generally indicates good stability on the bike.

Vertical knee track with close-together lines indicating good stability and proper bike positioning

Advantages of Velogic Studio's knee track vs webcam + laser

• The information is available as a single image, rather than a video - so it can be included in the report.

• The information is averaged over many pedal strokes, so one odd pedal stroke doesn't give unrepresentative data

• The direction of travel is clearly indicated, by color & arrowheads

• No additional hardware or fitter interaction required; knee track is collected as a byproduct of a normal capture

• You can more easily compare changes in knee track, using overlay and morph comparisons (see Reviewing fit artifacts)