Movement assessment glossary

Gait

Gait is the pattern of movement produced by walking. It is described by the repeating cycle each limb goes through and by the distance and timing measures derived from that cycle.

Clinically, gait is assessed both by observation and by measurement. Observation captures qualitative features; measurement reduces the walk to parameters such as walking speed, cadence, and stride length that can be compared over time.

Gait cycle

Also known as: Stride cycle.

One gait cycle runs from initial contact of one foot to the next initial contact of the same foot. It divides into stance, when the foot is on the ground, and swing, when it is not.

At usual walking pace, stance occupies roughly 60 percent of the cycle and swing roughly 40 percent, with two brief periods of double support where the limbs overlap.

Gait speed

Also known as: Walking speed, Usual gait speed.

Gait speed is the distance walked divided by the time taken, reported in meters per second. Usual-pace gait speed over a marked 4-meter or 10-meter course is the standard clinical form.

Gait speed has been described as the sixth vital sign because it is quick to measure, reliable, and associated with outcomes including survival in older adults.

Cadence

Also known as: Step rate.

Cadence is the number of steps taken per minute. Together with step length it determines walking speed, so two people walking at the same speed can have different cadences.

Stride length

Stride length is the distance between two consecutive initial contacts of the same foot — one full gait cycle of forward progression. Step length, by contrast, is the distance between contacts of opposite feet.

Stance phase

Also known as: Stance, Stance time.

Stance phase is the portion of the gait cycle during which a foot is in contact with the ground, bounded by initial contact and toe-off. It accounts for approximately 60 percent of the cycle at usual walking pace.

Stance is reported in seconds or as a percentage of the gait cycle. Because stance time in seconds shortens as walking speed increases, the percentage form is generally more comparable across visits.

Swing phase

Swing phase is the portion of the gait cycle during which a foot is off the ground, from toe-off to the next initial contact of the same foot. It accounts for approximately 40 percent of the cycle at usual walking pace.

Double support time

Double support is the part of the gait cycle in which both feet are in contact with the ground. There are two such periods per cycle, together making up roughly 20 percent of it at usual pace.

Double support tends to lengthen with cautious or unsteady walking, and can change before overall walking speed does.

Spatiotemporal gait parameters

Spatiotemporal gait parameters are the distance and timing measures that describe a walking pattern, including walking speed, cadence, step and stride length, step and stride time, stance and swing time, double support time, and step width.

Markerless motion capture

Also known as: Markerless motion analysis.

Markerless motion capture estimates the positions of body landmarks from video using computer-vision pose estimation, with nothing attached to the body. It contrasts with marker-based systems, which track reflective markers physically placed on the participant.

Pose estimation

Also known as: Human pose estimation, Key point detection.

Pose estimation is a computer vision method that locates anatomical key points, such as joint centers and body landmarks, within an image or video frame. Tracking those key points across frames produces the trajectories from which movement measures are derived.

Marker-based motion capture

Also known as: Optical motion capture, Laboratory motion capture.

Marker-based motion capture tracks reflective markers attached to the body using an array of fixed cameras. It is the reference standard for three-dimensional joint kinematics and requires dedicated laboratory space, camera calibration, and trained operators.

Timed Up and Go

Also known as: TUG.

The Timed Up and Go is a functional mobility test in which a person rises from a chair, walks three meters, turns, returns, and sits down. The result is the time taken to complete the whole sequence.

Because a single duration covers standing, walking, turning, and sitting, the total time does not indicate which component limited performance.

Sit-to-stand test

Also known as: STS, Chair stand test, Five-times sit-to-stand.

A sit-to-stand test measures the ability to rise from a seated position. Common forms are the five-times sit-to-stand, scored as time to complete five repetitions, and the 30-second chair stand, scored as the number of repetitions completed.

Performance outcome measure

Also known as: PerfO, Performance-based measure.

A performance outcome measure records the result of a defined task carried out by the patient. FDA guidance on clinical outcome assessments classifies it separately from patient-reported, observer-reported, and clinician-reported outcome measures.

Patient-reported outcome

Also known as: PRO, PROM.

A patient-reported outcome is a measurement of a patient’s health status reported directly by the patient, typically through a questionnaire, without interpretation by a clinician. It records how the patient feels or perceives their function.

Short Physical Performance Battery

Also known as: SPPB.

The Short Physical Performance Battery is a composite measure of lower extremity function combining standing balance, a timed walk, and a repeated chair stand, scored out of 12.

Frailty

Frailty is a state of reduced physiological reserve and increased vulnerability to stressors. The Fried phenotype defines it by the presence of three or more of five criteria: weight loss, exhaustion, low activity, weakness, and slowness.

Slowness in the phenotype is assessed by usual-pace gait speed, which is why gait measurement is central to frailty assessment.

Sarcopenia

Sarcopenia is a progressive loss of skeletal muscle mass and strength. The revised European consensus defines it by low muscle strength, confirmed by low muscle quantity or quality, with low physical performance indicating severe sarcopenia.

The consensus advises a single gait speed cut-off of 0.8 m/s or below as an indicator of severe sarcopenia.

Minimal detectable change

Also known as: MDC.

Minimal detectable change is the smallest change in a measure that exceeds measurement error and can therefore be interpreted as real change rather than noise. It is specific to the measure, the population, and the measurement conditions.

It is distinct from minimal clinically important difference, which concerns whether a change matters to the patient rather than whether it can be detected.

Digital health technology

Also known as: DHT.

In the clinical trial context, a digital health technology is a system that uses computing platforms, connectivity, software, or sensors to acquire health data remotely. FDA guidance addresses their selection, verification, validation, and data handling in clinical investigations.

Verification and validation

For a digital health technology, verification is objective evidence that the parameter measured is measured accurately and precisely. Validation is objective evidence that the technology appropriately assesses the clinical event or characteristic in the intended population.

The two are distinct: a technology can be well verified and still not validated for the population in a given trial.

Fit-for-purpose

A measurement approach is fit for purpose when the evidence supporting it is sufficient to justify its use for a specific context of use — a particular endpoint, in a particular population, in a particular investigation.

Spatial calibration reference

Also known as: Calibration marker, Calibration floor marker.

A spatial calibration reference is a known real-world dimension present in a recorded scene. Camera-based measurement requires one in order to convert distances measured in image pixels into physical units.

Decentralized clinical trial

Also known as: DCT, Remote trial, Hybrid trial.

A decentralized clinical trial conducts some or all trial activities away from a traditional investigator site, with data collected at the participant’s location. A hybrid design combines on-site visits with remote data collection.