Balance, Roll and Footprint — what each index measures

Why three numbers rather than one

A single score is easy to follow and useless on its own: when it moves, you want to know what moved. The three indices answer three different questions, and they can move independently. Someone can be sharing weight evenly between the feet while still rolling through the step poorly, or rolling well while loading one part of the foot far more than they used to.

Balance Index — are you using the foot?

Balance describes how weight is distributed between left and right, in two senses: how much force each foot takes, and how long each foot spends on the ground. Both matter, and they can disagree. It is possible to take almost equal force through both feet while still spending noticeably less time on one of them.

Left-right comparisons are scaled so that the foot carrying more load that day reads 100 and the other reads as a percentage of it. This is a relative comparison — it describes how evenly weight is shared, not how hard either foot is pressing in absolute terms. Symmetry is the lower value divided by the higher one: 100% means the two sides are equal, and lower numbers mean a bigger gap.

Balance is usually the first index to move when a limb is being protected, because protecting a leg almost always means spending less time on it.

Roll Index — are you using it well?

A step is not a single event. Load arrives at the heel, travels forward through the midfoot, and leaves through the forefoot at push-off. Roll scores how cleanly that transition happens, from 0 to 100, and breaks the score into heel strike, midstance and toe-off so you can see which part of the step is lagging.

The calculation deliberately ignores the worst steps of the day. A day’s steps are ranked from worst to best, the bottom third are discarded — these tend to be moments where you were shuffling around a kitchen rather than really walking — and the rest are averaged. Without that, the score would mostly measure how much pottering you did.

Push-off is typically the last part to come back after an ankle or foot injury, because it is the part that asks most of the joint.

Footprint Index — where does the load sit?

The insole reads ten zones on each foot. Footprint shades each zone by its typical peak pressure for the day, relative to the other nine zones on the same foot. It shows where pressure concentrates, how the two feet compare with each other, and how both shift from one month to the next.

The relative scaling is the important caveat. Footprint is not a calibrated absolute pressure reading in kilopascals, and Stride One should not be used as though it were one. It is a map of distribution and change, which is a different and more robust thing to measure with a consumer device.

What is recorded underneath the indices

The parameters Stride One records are: plantar pressure distribution across foot zones, load and weight-bearing, left and right force sharing, stance-time sharing, the quality of the heel–midfoot–push-off transition, cadence, stance time, double-support time, and step-time variability.

What is not measured

This list matters as much as the one above, and you will find it stated on every page where it is relevant. Stride One does not measure gait speed or walking velocity, step length, stride length, step width, or skin temperature.

Those absences have consequences we would rather name than skirt. Much of the best-known gait research — including the work behind the idea that walking is a general health indicator — is built on gait speed. Some of the most discriminating fall-risk parameters are built on step-width variability. Charcot-detection research is built on skin temperature. None of those are things this device can show you, and we do not present them as though they were.

How trends are worked out

A trend arrow compares today’s value with the average of the last seven days, including today. Only days with recorded data count towards the average — a day you did not wear them is left out rather than counted as zero. A dash means there is not yet enough data to compare.

The fuller reference, including how the seven-day pressure history and the loading distributions are built, is on the reading your data page.

What Stride One does and does not do

Stride One is a monitoring device. It records how load is shared between the feet, how the foot rolls through each step, and how pressure is distributed across the zones of each foot. It gives you, and anyone you choose to share it with, a record of how those things change.

It does not diagnose anything, detect any condition, predict any outcome, or tell you what to do about what it shows. It does not measure skin temperature, gait speed, step length, stride length or step width. It does not replace an appointment, an examination or your clinician’s judgement.

Sources

• Ceriter, Stride One data definitions — reading your data.
• Ceriter, Stride One user manual — manual.

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