Spasticity is tested by moving a joint passively while the person stays relaxed, then grading how much the muscle resists that movement. The hallmark of spasticity is that resistance increases with speed: the faster you stretch the muscle, the stronger it pushes back. This velocity-dependent quality is what separates spasticity from other forms of muscle tightness, and every clinical test for it is built around that principle.
What Examiners Are Looking For
Spasticity results from damage to the nerve pathways that normally keep reflexes in check. When that braking system is lost, the spinal cord’s stretch reflex becomes hypersensitive, so muscles contract too forcefully whenever they’re lengthened. During a physical exam, the clinician moves the affected limb at different speeds. At slow speeds, the limb may feel relatively normal. At faster speeds, they’ll feel a sudden “catch,” a moment where the muscle abruptly locks up before releasing. That catch is the signature finding.
Beyond the catch, examiners also look for clonus, a rhythmic bouncing of the muscle that alternates between contraction and relaxation when you hold a joint in a stretched position. The ankle is the most common place to check for it. A few beats of clonus can be normal, but sustained clonus points to significant spasticity.
The Modified Ashworth Scale
The Modified Ashworth Scale (MAS) is the most widely used bedside tool for grading spasticity. The examiner moves the joint through its full range of motion over about one second, then assigns a score from 0 to 4:
- 0: No increase in muscle tone.
- 1: Slight increase, with a catch and release or minimal resistance at the end of the range.
- 1+: A catch followed by minimal resistance through less than half of the range.
- 2: Marked increase in tone through most of the range, but the limb can still be moved easily.
- 3: Considerable increase in tone, and passive movement is difficult.
- 4: The limb is rigid in a fixed position.
The MAS is quick and requires no equipment, which is why it dominates clinical practice. Its main weakness is consistency between examiners. Studies report inter-rater reliability ranging from slight to moderate depending on the joint tested, with the ankle plantar flexors performing worst. The descriptions for grades 1, 1+, and 2 are close enough that two clinicians testing the same patient will disagree by one grade roughly 40% of the time. A large part of the problem is that the scale doesn’t specify exactly how fast the examiner should move the limb, so each clinician’s “one second” differs slightly.
The Modified Tardieu Scale
The Modified Tardieu Scale (MTS) tries to solve the speed problem by testing at two distinct velocities. First, the examiner moves the joint slowly (V1) through its full range to establish a baseline. Then they move it as fast as possible (V3). During the fast stretch, the examiner stops at the exact point where the muscle reacts, the “angle of muscle reaction.” The difference between the resting range found at slow speed and the catch angle found at fast speed reflects how much of the tightness is truly spasticity versus structural shortening of the muscle or joint.
This distinction matters for treatment planning. If the range of motion is limited even at slow speeds, the problem is likely a contracture (permanent shortening of soft tissue), which won’t respond to treatments that target nerve-driven spasticity. If the range is full at slow speed but catches early at fast speed, spasticity is the primary issue. The Tardieu Scale captures this nuance in a way the Ashworth Scale does not.
The Pendulum Test
The pendulum test, originally introduced by neurologist Robert Wartenberg, offers a more hands-off assessment of knee extensor spasticity. The person sits in a semi-reclined position with their legs hanging freely over the edge of the table. The examiner lifts the lower leg to horizontal, then releases it and lets gravity take over. In someone without spasticity, the leg swings back and forth like a pendulum, gradually losing momentum until it hangs still. In someone with spasticity, the leg barely swings. It may stop after one incomplete arc or reverse direction abruptly.
Clinicians quantify this by tracking the peak angles of each swing. The “relaxation index” compares the first swing’s amplitude to the final resting angle. A lower relaxation index indicates more resistance and more spasticity. Because the test relies on gravity rather than the examiner’s hand, it removes some of the human variability that plagues manual scales.
Telling Spasticity Apart From Rigidity
One of the most important parts of testing for spasticity is making sure it’s actually spasticity and not rigidity, which feels similar but comes from a completely different cause. Rigidity, commonly seen in Parkinson’s disease, produces constant resistance throughout the entire range of motion regardless of speed. You can move the joint as slowly as you like and the stiffness stays the same, often described as a “lead pipe” quality. If a tremor is also present, the resistance takes on a ratcheting quality called “cogwheeling.”
Spasticity, by contrast, is asymmetric. It typically affects one group of muscles more than their opposites (flexors in the arm, extensors in the leg), and the resistance only kicks in once you move the joint quickly enough to trigger the stretch reflex. This speed-dependent catch is the clearest way to distinguish the two at the bedside.
Surface Electromyography
For research settings or cases where precise measurement matters, surface electromyography (sEMG) provides an objective layer on top of manual scales. Electrodes placed on the skin over the muscle record electrical activity during passive stretching. In spastic muscles, certain electrical signals correlate strongly with Ashworth scores. Time-based measures of muscle activation show strong positive correlations with spasticity grades, while frequency-based measures trend in the opposite direction. Automated classification systems using data from multiple electrode channels can now grade spasticity with accuracy that matches or exceeds manual assessment. These tools aren’t part of routine clinical exams, but they’re increasingly used in rehabilitation research and to track treatment response in specialized centers.
How to Prepare for a Spasticity Assessment
Accurate results depend heavily on conditions at the time of testing. Several factors can temporarily worsen spasticity and inflate scores: a full bladder, constipation, pain, infection, tight clothing, emotional stress, and even the temperature of the room. Clinicians following current best practices from the American Academy of Physical Medicine and Rehabilitation are advised to ensure patients are medically stable and to address any reversible triggers before testing.
Positioning also matters. The person being tested needs to be as relaxed as possible, since voluntary muscle activation will confuse the results. For upper limb testing, lying on your back with the arm supported is standard. For lower limb testing, lying flat or semi-reclined with the leg off the edge of the table works for most muscle groups. The joint should start in a consistent position each time, especially if the goal is to track changes over weeks or months of treatment.
Current consensus guidelines emphasize that the same measurement tool should be used at every visit. Switching from the Ashworth Scale to the Tardieu Scale mid-treatment makes it impossible to compare scores meaningfully. Reassessment should happen before or at the time of each treatment session, and results should be tied to specific, patient-centered goals rather than just a number on a scale.