Stride Velocity 95th Centile as a Digital Biomarker

Stride velocity 95th centile is the walking speed a person reaches at the 95th centile of all strides recorded over a monitoring period. It describes their fastest ordinary walking rather than their average, which is a deliberate design choice: average speed in daily life is dominated by short, slow, incidental movement, while the upper tail reflects what the person is still capable of doing.

It holds a distinct place in this library. In 2023 the European Medicines Agency issued a qualification opinion supporting its use as a primary endpoint in studies of ambulatory Duchenne muscular dystrophy, making it the first wearable derived digital measure to reach that status in Europe. Every other measure in this directory is discussed against that precedent.

It is treated as its own entry rather than folded into gait speed because the statistic, the device, the wear protocol and the regulatory scope are all specific to it.

Measurement uses a magneto inertial sensor worn continuously at the ankle, which records stride by stride kinematics rather than sampling. Strides are detected and their velocity computed individually, then the distribution of all valid strides over the recording period is taken and the 95th centile extracted.

The recording period matters. Because the statistic sits in the tail of a distribution, it needs enough strides for that tail to be stable, which in practice means continuous wear across days rather than a single session. Normative data on spontaneous stride velocity, stride length and walking activity in unconstrained settings has been published to support interpretation.

The qualification is tied to this measurement chain. A different device, placement or algorithm producing a nominally similar statistic does not inherit the regulatory position.

The primary use is as an endpoint in Duchenne muscular dystrophy trials, where population sizes are small and endpoint sensitivity has direct consequences for whether a treatment effect can be detected at all. Work comparing it against conventional assessment has reported that it detects decline over shorter intervals than the six minute walk test, which is the practical argument for adopting it.

The second use is as the reference case for the wider field. When a sponsor asks what it takes for a digital measure to become a primary endpoint, this is the worked example: a defined population, a fixed measurement chain, normative data, and a formal qualification procedure rather than a single trial submission.

It is reported alongside the six minute walk test and functional scales, which supply continuity with the existing evidence base.

The qualification is narrow and is routinely overstated. It applies to ambulatory Duchenne muscular dystrophy from around four years of age, with a specified device and processing pipeline. It is not a general endorsement of wearable gait measurement, and citing it as though any wearable speed measure now has regulatory standing is the most common misuse of this precedent.

Ankle wear is less tolerable than wrist wear for long periods, and adherence is a real constraint in paediatric populations. As the disease progresses and ambulation is lost, the measure floors out and stops discriminating, which limits the window in which it is useful.

The North Star Ambulatory Assessment, the functional scale it is usually compared against, is not currently in this library, which leaves the instrument bridge for this page incomplete.

• Servais L, et al. Stride velocity 95th centile: insights into gaining regulatory qualification of the first wearable-derived digital endpoint for use in Duchenne muscular dystrophy trials. J Neuromuscul Dis. 2022. pubmed.ncbi.nlm.nih.gov
• European Medicines Agency. Qualification opinion on stride velocity 95th centile as primary endpoint in studies in ambulatory Duchenne muscular dystrophy. 2023. ema.europa.eu
• Poleur M, et al. Normative data on spontaneous stride velocity, stride length, and walking activity in a non-controlled environment. Orphanet J Rare Dis. 2021. pubmed.ncbi.nlm.nih.gov
• Rabbia M, et al. Stride velocity 95th centile detects decline in ambulatory function over shorter intervals than the 6-minute walk test in Duchenne muscular dystrophy. J Neuromuscul Dis. 2024. pubmed.ncbi.nlm.nih.gov