What is smartphone gait analysis and how does it work?

What the sensors in a smartphone actually measure

Every modern smartphone contains an inertial measurement unit, or IMU. It combines two sensors that between them describe how the phone is moving through space.

• The accelerometer measures linear acceleration along three axes, including the constant pull of gravity. Walking produces a highly characteristic repeating acceleration pattern.
• The gyroscope measures rotational velocity around those same three axes, which helps establish the phone’s orientation and separate genuine movement from tilt.

Gait analysis software reads these signals many times a second, identifies the repeating events within them — such as the moment each foot contacts the ground — and derives movement measures from the timing and pattern of those events.

From raw signal to gait measures

1. 1The IMU signal is sampled continuously while the person walks.
2. 2The signal is filtered to reduce noise from sensor drift and incidental movement.
3. 3Gait events are detected within the repeating pattern, marking the boundaries of each step and each full gait cycle.
4. 4Temporal measures are calculated from the timing between those events.
5. 5Spatial measures are estimated by combining the timing with the acceleration pattern.
6. 6Measures are averaged across the walking bout to produce a summary for that assessment.

Which measures are commonly derived

• Gait speed — how fast the person walks, one of the most widely used functional measures in movement science.
• Cadence — steps per minute.
• Step length and stride length — the distance covered by a single step and by a full gait cycle.
• Step time and cycle time — the duration of a single step and of a full gait cycle.
• Stance time and swing time — how long each leg spends supporting body weight versus swinging through.
• Double support time — the portion of the cycle when both feet are in contact with the ground, often reported as initial and terminal double support.

Temporal measures depend mainly on accurate event detection, which is why they tend to be the most reliably reproduced. Spatial measures such as step and stride length involve additional estimation and are correspondingly harder.

Why phone placement matters

The IMU records the movement of the phone, not of the legs. Where the phone sits therefore changes what the signal contains.

• Secured near the waist, close to the body’s centre of mass, the phone captures a clean, symmetrical trunk-movement signal that suits whole-body gait measures.
• In a trouser pocket, the signal is dominated by the movement of one leg and is affected by how loosely the phone sits.
• Held in the hand or carried in a bag, arm swing and incidental movement contaminate the signal.

Because placement changes the signal, any specific accuracy result should state the placement used during testing.

Advantages of smartphone gait measurement

• No specialist hardware — the sensor is already in the person’s pocket.
• Assessment can happen wherever the person is, rather than only in a clinic or laboratory.
• Measurement is objective and numerical, so change over time can be compared consistently.
• Repeat assessment is inexpensive, which makes tracking recovery or deterioration practical.
• Nothing needs to be posted, fitted, charged or returned.

Factors that shape the measurement

• Accuracy is parameter-specific: some gait measures agree closely with laboratory reference methods and others do not.
• A single waist-worn sensor cannot straightforwardly separate left from right, so side-specific analysis needs a different configuration.
• Sensor hardware and sampling behaviour vary between phone models.
• The person must be able to walk safely and follow the instructions unsupervised for the result to be meaningful.
• Short walking bouts give fewer gait cycles to average across, which reduces stability.
• Kinetics — forces and moments — cannot be measured this way at all.

Compared with laboratory gait analysis

An instrumented gait laboratory using marker-based 3D motion capture and force plates remains the reference standard. It measures full three-dimensional joint kinematics and ground reaction forces with a precision no smartphone approaches.

The trade-off is access. A laboratory session requires the person to travel, specialist staff time, marker placement and calibration, and is realistically repeated a handful of times at most. Smartphone measurement covers a much narrower set of measures, but can be repeated frequently and wherever the person is. The two answer different questions rather than competing directly.

Compared with dedicated wearable IMU sensors

Research-grade wearable IMUs use the same physical principle as a smartphone. They typically offer higher and more consistent sampling rates, tighter fixation to the body, and the option of using several sensors at once — which is what makes reliable side-specific analysis possible.

Their cost is logistical: devices must be procured, fitted correctly, charged, synchronised, collected and maintained. For studies needing multi-segment measurement they are the better tool. For repeated functional measurement at scale, using the phone the person already owns removes most of that overhead.

What MoveLab’s own published evidence shows

MoveLab’s 2025 peer-reviewed validation study compared smartphone-derived gait measures against gold-standard marker-based 3D motion capture, and Timed Up and Go and 30-second Sit-to-Stand against clinical-standard scoring.

The study included 25 healthy adults in a controlled laboratory, with the smartphone secured in a pouch at the waist. The publication page sets out the parameter-by-parameter results in full.