In the field of physical therapy, a patient’s ability to move their joints is a primary metric for evaluating health and recovery. This ability is quantified as Range of Motion (ROM), which measures how far a joint can move in various directions before being stopped by surrounding tissue or pain. Assessing ROM is a fundamental step for physical therapists as it provides objective data about the functional capacity of muscles and joints.
What Active Range of Motion Means
Active Range of Motion (AROM) is the degree of movement a person can achieve at a joint solely through the contraction of their own muscles. This movement is performed completely independently, requiring the patient to voluntarily engage the muscles responsible for moving the joint through its available arc, without assistance from external forces.
This measurement provides a direct reflection of several factors, including the patient’s willingness to move, the coordination of muscle groups, and the strength of contractile tissues (muscles and tendons). AROM is often one of the first parameters evaluated to establish a baseline for treatment and track progress.
How AROM Differs from Other Movements
To fully understand AROM, it is useful to compare it with the other two primary categories of joint movement assessment used in physical therapy: Passive Range of Motion (PROM) and Active Assisted Range of Motion (AAROM). The distinction between these three measurements lies entirely in the source of the force that moves the body segment.
Passive Range of Motion (PROM) occurs when an external force, such as a physical therapist or a specialized machine, moves the joint while the patient’s muscles remain completely relaxed. The therapist is essentially doing all the work, which allows the measurement to test the mechanical integrity of the joint capsule, ligaments, and cartilage. Since the muscles are not contracting, PROM generally reflects the maximum possible flexibility of the joint and is typically greater than AROM in a healthy individual.
Active Assisted Range of Motion (AAROM) is the middle ground between the two, used when a patient can initiate movement but cannot complete the full range on their own. In AAROM, the patient actively contracts their muscles to move the joint as far as they can, and an external force then provides the necessary supplemental support to finish the movement. This technique is often used early in rehabilitation to allow the patient to engage their muscles while protecting a healing structure from excessive strain.
The comparison between AROM and PROM is particularly diagnostic for a therapist, forming what is known as the “ROM arc.” If AROM is limited but PROM is full, the problem is likely related to muscle weakness, pain inhibition, or a neurological issue rather than a structural joint limitation. Conversely, if both AROM and PROM are limited, the restriction is often due to a non-contractile issue, such as joint stiffness, capsular tightness, or bony block.
Assessing AROM and Its Diagnostic Value
The assessment of AROM in a clinical setting provides objective data that directs the rehabilitation plan. Physical therapists primarily use a tool called a goniometer to precisely measure the joint angles achieved during active movement. This instrument features a stationary arm, a movable arm, and a central fulcrum, which is aligned over the joint’s axis of rotation to measure movement in degrees.
The therapist positions the patient in a standardized anatomical position and asks them to move the joint through its full available range without assistance. The resulting angle is recorded and compared against established normative values for that specific joint, age, and gender. Testing the unaffected side first provides an immediate benchmark for comparison against the injured or problematic side.
A restricted AROM is diagnostically significant because it suggests a problem with the structures responsible for generating motion, specifically the contractile tissues (muscles and tendons). Limitations may be caused by muscle weakness, nerve impairment that prevents full muscle activation, or pain that inhibits the patient from attempting the full motion.