positus
positus
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Method and research

How Positus measures movement.

Markerless motion capture from two phones, grounded in published biomechanics research.

From two videos
to measurements.

Positus uses markerless motion capture. Nothing is attached to the body; the measurements come from ordinary video.

  1. 01

    Two views

    Two phones record the same movement at the same time, from different angles.

  2. 02

    Body landmarks

    Software locates body landmarks, such as the joints, in every frame of each video.

  3. 03

    Movement in three dimensions

    The two views are combined into a three-dimensional estimate of the movement, from which joint angles and body positions are calculated.

Every point becomes a measurement.

Joint kinematics through every repetition, walking, running or exercising, and how movement changes as fatigue builds.

Illustrative movement, not patient data. The phones, rays, body and readouts are drawn to explain the method, not recorded.

The movement study on the home page shows the kind of measurements this produces, using an illustrative figure.

The research behind
markerless capture.

Markerless motion capture measures how the body moves from ordinary video: joint angles, body position and the timing of each step, with nothing attached to the body.

Published studies comparing it with marker-based laboratory systems report joint angles within a few degrees during walking and everyday movements, and consistent results from one session to the next. A selection:

  1. Uhlrich and colleagues, 2023

    OpenCap: Human movement dynamics from smartphone videos

    PLOS Computational Biology

    Two smartphones measured joint angles during walking, squats, sit-to-stand and jumping in 10 adults, with a mean absolute error of 4.5 degrees against marker-based motion capture.

    People
    10 adults
    Movements
    Walking, squats, sit-to-stand, jumping
    Setup
    Two smartphones against marker-based motion capture
    doi.org/10.1371/journal.pcbi.1011462

  2. Kanko and colleagues, 2021

    Concurrent assessment of gait kinematics using marker-based and markerless motion capture

    Journal of Biomechanics

    In 30 adults walking on a treadmill, markerless and marker-based estimates of hip, knee and ankle joint centres agreed within 2.2 to 3.6 centimeters.

    People
    30 adults
    Movements
    Treadmill walking
    Setup
    A video-based markerless system against marker-based motion capture, recorded together
    doi.org/10.1016/j.jbiomech.2021.110665

  3. Kanko and colleagues, 2021

    Inter-session repeatability of markerless motion capture gait kinematics

    Journal of Biomechanics

    In 8 adults recorded in three sessions about a week apart, variability between sessions (2.8 degrees) was close to variability between walking trials within one session (2.5 degrees).

    People
    8 adults
    Movements
    Walking
    Setup
    Three sessions about a week apart
    doi.org/10.1016/j.jbiomech.2021.110422

  4. Song and colleagues, 2023

    Markerless motion capture estimates of lower extremity kinematics and kinetics are comparable to marker-based across 8 movements

    Journal of Biomechanics

    Across eight movements in 10 adults, knee and ankle angles differed from marker-based capture by less than 5.9 degrees.

    People
    10 adults
    Movements
    Eight movements
    Setup
    Markerless against marker-based capture, joint angles and forces
    doi.org/10.1016/j.jbiomech.2023.111751

Each study describes the system, people and movements it tested.

See Positus in a
clinical workflow.

Walk through the capture process, explore the measurements, and discuss how Positus could fit into your practice.

Request a demo
  • Two ordinary phones and a clear capture area.
  • Opens your email app. Business inquiries only.
  • Please do not include patient information.