How far a joint can move.
Range of motion (ROM) is the amount of movement available at a joint, expressed in degrees relative to a defined starting position. Active ROM (AROM) is produced by the patient's own muscle contraction, while passive ROM (PROM) is produced by an external force, typically the clinician, with the patient relaxed. Comparing the two helps separate a muscular or motor problem from a joint or soft-tissue restriction.
ROM gives the clinician an objective, trackable number to support decisions on diagnosis, treatment progression and discharge readiness. A gap between AROM and PROM points toward weakness, pain inhibition or a neurological deficit rather than true joint restriction, which changes the treatment approach. Serial measurements over time also provide evidence of progress or plateau that can justify continuing, modifying or ending an intervention.
ROM is most commonly measured with a universal goniometer aligned to standardised bony landmarks, though inclinometers, visual estimation or motion-capture systems are also used depending on setting and required precision. The clinician records the joint, the movement plane, and whether the measurement is active or passive, comparing findings to normative values or the contralateral side. Measurements are typically retaken at intervals to track change following injury, surgery or intervention.
Goniometric measurement has notable inter- and intra-rater variability, so small differences between sessions may reflect measurement error rather than real change unless the same rater and technique are used consistently. ROM alone says nothing about pain, quality of movement, strength or functional capacity, so a joint can have full ROM and still be clinically impaired, or restricted ROM may not correlate with disability. It is also commonly overused as a stand-alone outcome measure without being tied back to a functional goal relevant to the patient.