Dead Spot Score Explained (Part 1)

Hello, I’m Fukuma from LEOMO. Today I’ll be introducing the history and physics behind LEOMO’s DSS (Dead Spot Score) metric. DSS is one of the original MPIs (Motion Performance Indicators) offered by the LEOMO TYPE-R.

What does DSS measure?

DSS is recorded by two motion sensors, the left foot sensor, and the right foot sensor. You can see this value live on the TYPE-R head unit, and in detail on the LEOMO web app when you upload your activity.

DSS shows:

  • Where Dead Spots are occuring in your pedaling cycle
  • The magnitude of each Dead Spot
  • The total magnitude of Dead Spots per crank revolution

What exactly is a Dead Spot?

LEOMO defines a Dead Spot as a place in your pedaling cycle where the smoothness of the foot’s rotational motion (along the pedal axis, not the crank axis) has been lost. This rotational motion is the seesaw-like motion that occurs as your heel moves up and down while pedaling.

There are many reasons why a Dead Spot occurs while pedaling. However,the key point to remember is that there is inefficiency in power transfer at that point, meaning wasted pedaling energy, hence Dead Spot. We’ve heard from some of our riders that they believe that dead spots occurring at the 12 and 6 o’clock positions are expected, since that is where the legs switch motions from a pulling up motion to a pushing down motion. However, we have found that those with smooth pedaling have no Dead Spots at these positions. We’ve also found that some cyclists have dead spots in completely different sections along a pedaling cycle.

Dead Spots from a physics standpoint

The two graphs below represent the rotation speed of the foot, for smooth and unsmooth pedaling. The rotation speeds for heel-down and heel-up motions alternate between a positive and negative value. Moving the heel downwards will show a negative speed (below 0), and moving the heel upwards will show a positive speed (above 0).

Smooth pedaling with little to no dead spots

For smooth pedaling motions, the speed will be represented with smooth, undulating curves.

LEOMO DSS Part 1-2

Unsmooth pedaling with dead spots

However, unsmooth pedaling will be represented by a disturbed waveform. See the dented tops on the upper crests? These are Dead Spots.

LEOMO DSS Part 1-3

DSS and Performance

How does DSS correlate with performance?

Early in LEOMO’s research, we used multiple samples from various cyclists in different performance ranges to try to find patterns in the data. Using raw motion data from multiple cyclists, we found that the shape of the waveform for the foot rotation speed was one of the key differentiators between the samples collected. We created the DSS algorithm to measure this key difference. Then, when comparing the data between domestic professional cyclists and amateur competitive cyclists, the former tended to have much less Dead Spots than the latter. Also, we found that professional cyclists’ Dead Spots tended to increase when fatigued, such as during the end of a long training session.

By working with several coaches, we were able to compare their qualitative observations with our quantified motion data. We found that rides that had high DSS were described in various ways by coaches: “his pedaling was unsmooth,” “her pedaling looked rough and uneven,” “he’s really struggling,” “the saddle is too high,” etc.

We see that there is a relationship with DSS and inefficient or problematic pedaling. High DSS, however, does not always equal bad performance, since DSS is a secondary phenomenon to a primary phenomenon such as a too-high saddle height. However, having less Dead Spots can be said to signify a more power-efficient pedaling stroke.

Dead Spots cannot always be seen by the eye, and the LEOMO TYPE-R can help to capture these qualitative observations into a measurable metric. This allows for easier communication between athletes and coaches.

In the next article, let’s go deeper into exactly what sort of pedaling is causing Dead Spots, with both data and movies.

 


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