Passive range of motion (PROM) is the movement a joint can achieve when someone or something else moves it for you, without any effort from your own muscles. A therapist lifts your arm, a family member bends your knee, or a machine moves your ankle through its arc. Your muscles stay completely relaxed while the joint travels through its available movement. This distinguishes it from active range of motion, where you power the movement yourself.
How PROM Differs From Active and Active-Assisted Motion
Range of motion falls into three categories, and the difference comes down to who is doing the work. Active range of motion (AROM) is any movement you perform independently, using your own muscle contraction. Active-assisted range of motion (AAROM) is a hybrid: you contract your muscles as much as you can, and an outside force picks up the slack, whether that’s a therapist’s hands, a pulley system, or even gravity. Passive range of motion removes your effort entirely. The movement comes from an external source while your muscles stay inactive.
This distinction matters clinically because the three types reveal different things about a joint. If your passive range is significantly greater than your active range, the joint itself is structurally fine but the muscles around it are too weak, too painful, or neurologically unable to move it through its full arc. If passive range is also restricted, the problem is more likely in the joint structure itself, the surrounding soft tissue, or both.
Why PROM Is Used in Rehabilitation
Passive range of motion exercises serve people who cannot move a joint on their own. This includes patients recovering from surgery on tendons, ligaments, or joints, people with paralysis or severe weakness after a stroke, and individuals on prolonged bed rest. The primary goal is to maintain or increase joint mobility by influencing the flexibility of the soft tissues surrounding the joint, including muscles, tendons, and the joint capsule itself.
When a joint stays still for too long, the tissues around it begin to stiffen and shorten. This leads to contractures, a condition where the joint loses its ability to fully extend or bend because the overlying soft tissue has become rigid. Passive movement is thought to prevent this by keeping collagen fibers from forming sticky cross-bridges that bind tissues together. It may also help maintain the natural length and pliability of muscles and tendons. In people with neurological conditions like stroke, passive movement can reduce spasticity, the excessive muscle tightness that resists any attempt to move a limb, by calming the overexcitable nerve signals driving that tension.
After total knee replacement, for example, passive and active-assisted exercises typically begin within the first three days. A common early goal is reaching at least 80 degrees of knee bend through both passive and active motion, enough to stand up from a seated position without compensating with other parts of your body.
How PROM Is Performed and Measured
During a passive range of motion exercise, the person performing it stabilizes the upper part of the joint, then slowly moves the lower part through the joint’s full available arc until reaching what clinicians call the “end feel,” the natural resistance at the limit of movement. The movement should be smooth and controlled. You should not feel sharp pain.
To measure PROM precisely, a clinician uses a goniometer, a protractor-like tool with two arms that align along the bones on either side of a joint. The therapist identifies bony landmarks by touch, aligns the device, moves the joint passively to its end range, and reads the angle. This measurement provides a baseline and tracks progress over weeks of rehabilitation. The numbers also help identify whether a restriction is getting better, staying the same, or worsening.
Continuous Passive Motion Machines
A continuous passive motion (CPM) machine is a motorized device that moves a joint back and forth through a preset arc without any effort from the patient. Introduced in the early 1980s, these machines became common after knee replacement surgery. The idea was straightforward: if immobility causes stiffness, then continuous gentle movement should prevent it.
The evidence, however, is mixed. A Cochrane review found that CPM combined with physical therapy produced slightly better short-term range of motion compared to physical therapy alone. But when researchers followed patients out to six weeks and three months, those short-term gains disappeared. No lasting differences in range of motion or functional ability were detected between patients who used CPM and those who didn’t. Because of this, many clinicians have moved away from routine CPM use, favoring hands-on therapy and early active movement instead.
When Passive Movement Should Be Avoided
Passive range of motion is not appropriate for every situation. It is contraindicated immediately following a tear to a ligament, tendon, or muscle, since moving the joint could disrupt healing tissue. The same applies near an unhealed fracture (unless specifically directed by an orthopedic surgeon) and right after surgical repair of tendons, ligaments, the joint capsule, or surrounding skin.
If a joint appears hot, red, or swollen, passive movement should be paused. These are signs of active inflammation or possible infection, and moving the joint can make things worse. When performing PROM, you should only move the joint within its currently available range. Pushing past a restriction without specific guidance from a physical or occupational therapist risks damaging the structures you’re trying to protect.
PROM for Spasticity After Stroke
Stretching through passive movement is the most widely used physical technique for managing spasticity after a stroke. The goal is to reduce pain, maintain soft tissue flexibility, and normalize muscle tone in limbs that have become stiff due to overactive nerve signals. Several small studies have shown that passive stretching can temporarily reduce spasticity and improve joint range, but the effects tend to be short-lived. In one study, spasticity improved significantly during a course of passive dynamic stretching but increased again within a week after treatment stopped.
A systematic review and meta-analysis looking across multiple studies found no statistically significant overall benefit of stretching for spasticity after stroke. This doesn’t mean it’s useless. Individual studies do show improvements in specific patients, and maintaining joint mobility remains important for preventing contractures in paralyzed or weakened limbs. The takeaway is that passive movement for spasticity works best as one component of a broader rehabilitation program rather than a standalone treatment.