Three ways to measure the same movement
A clinician who wants objective movement data has more options than ever. Inertial sensors worn on the body, force plates built into the floor, and markerless capture that runs on a phone camera all produce numbers where there used to be an impression. They are not interchangeable, though. Each was designed around a different tradeoff between accuracy, setup, and where the measurement can happen—and understanding those tradeoffs matters more than chasing whichever tool sounds most advanced.
What wearables and force plates do well
Wearable inertial sensors are strong at continuous, in-the-wild data: step counts, activity over a day, cadence during a long walk. Strapped to the right landmark, they capture motion the clinic never sees. Force plates, at the other end, are the reference standard for ground reaction forces and balance—precise, validated, and hard to beat for the specific things they measure.
The cost is friction. Wearables have to be placed correctly, charged, synced, and often worn for days, and placement drift changes the signal. Force plates are fixed, expensive, and confined to the settings that can house them. Both can produce excellent data, and both add steps that, on a full clinic day, quietly get skipped.
Where markerless smartphone capture fits
Markerless capture takes a different path: a standard phone camera, computer vision inferring movement across a set of body landmarks, and no hardware to attach to the patient. Nothing to place, charge, or sync. That lowers the barrier to actually taking the measurement—which is often the real bottleneck, since the most accurate instrument is worthless for the assessment that never gets done.
The relevant question isn't which method wins in the abstract. It's whether a tool captures the movements a given assessment depends on, does it consistently, and fits the visit. (For how markerless capture actually compares to laboratory reference systems, see the peer-reviewed accuracy evidence.) For visual, whole-body tasks—gait, balance, sit-to-stand, range of motion—a camera sees the whole picture at once, without instrumenting the body.
Consistency and access, not just accuracy
A lab-grade number from an instrument that only comes out occasionally tells you less over time than a slightly simpler number captured the same way every visit. Trends are what clinicians act on, and trends require repeated, standardized measurement. Removing setup friction and letting assessment happen in a normal exam room—or at home—is what makes that repetition realistic. Read alongside clinical judgment, the best tool is the one that reliably produces comparable data at the moment care is being delivered, not the one with the most impressive spec sheet.