The Modified Ashworth Scale (MAS) is a 6-point clinical tool used to grade muscle spasticity during passive movement. It requires no equipment, takes only a few minutes per muscle group, and remains the most widely used bedside measure of muscle tone in rehabilitation settings. Performing it correctly depends on understanding the movement technique, the scoring criteria, and the subtle differences between grades.
What the Scale Measures
The MAS measures resistance to passive movement. When you move a limb through its range of motion, you’re feeling for how much the muscle “fights back.” This resistance reflects increased muscle tone, which is common after stroke, spinal cord injury, traumatic brain injury, and in conditions like multiple sclerosis and cerebral palsy. The scale doesn’t measure strength, voluntary movement, or function. It only captures what happens when the examiner moves the limb while the patient stays relaxed.
Step-by-Step Administration
Start by positioning the patient comfortably, typically supine or seated depending on the muscle group being tested. The limb should be resting and fully supported so the patient isn’t actively contracting any muscles. Ask the patient to relax as much as possible before you begin.
To test a specific muscle group, move the limb passively through its full available range of motion. The movement should take about one second, roughly the count of “one-one-thousand.” This speed matters because spasticity is velocity-dependent: moving too slowly can mask tone that would appear at a normal pace. You’re looking for resistance, catches (a sudden brief increase in tone at a specific point), or rigidity as you move the joint.
For elbow flexors, for example, you would start with the elbow fully flexed and extend it through the full range. For knee extensors, start with the knee bent and straighten the leg. The key principle is that you move the limb in the direction that stretches the muscle group you’re assessing. Perform the movement a small number of times to get a clear sense of the resistance pattern, then assign a score.
The Scoring Criteria
The MAS uses six grades: 0, 1, 1+, 2, 3, and 4. Each describes a specific quality and amount of resistance you feel during the passive movement.
- Grade 0: No increase in muscle tone. The limb moves freely with no resistance beyond its normal weight.
- Grade 1: Slight increase in tone, with a catch and release or minimal resistance at the end of the range of motion. You feel something brief near the end of the movement, but it doesn’t persist.
- Grade 1+: Slight increase in tone, manifested as a catch followed by minimal resistance through less than half of the remaining range. The catch doesn’t simply release. Instead, you feel light resistance that continues but doesn’t last through the majority of the movement.
- Grade 2: A marked increase in tone through most of the range of motion, but the limb is still easily moved. You feel clear resistance throughout, yet you can complete the movement without much effort.
- Grade 3: Considerable increase in tone. Passive movement is difficult. You have to apply real force to move the limb through range.
- Grade 4: The affected part is rigid in flexion or extension. You cannot move the limb passively, or movement is negligible.
Distinguishing a 1 From a 1+
The difference between grades 1 and 1+ is the most common source of scoring confusion. Both involve slight increases in tone, but the pattern of resistance is different. With a grade of 1, you feel a brief catch or minimal resistance only at the very end of the range. It appears and then disappears quickly. With a 1+, you feel a catch at some point during the movement, and after that catch, light resistance lingers through a portion of the remaining range, but that portion is less than half the total movement. If the resistance continues through more than half the range, you’re looking at a grade 2.
Think of it this way: grade 1 is a bump at the finish line, while 1+ is a bump followed by a short drag. Grade 2 is resistance you feel nearly the whole way through.
Tips for Consistent Testing
Consistency across assessments matters, especially when tracking a patient’s progress over time. Several practical steps help improve accuracy.
Always test the same muscle group in the same position. Changing the patient’s posture between sessions can alter tone and make scores unreliable. Keep the speed of movement as consistent as possible, aiming for that one-second count through the full range each time. If the patient is anxious, in pain, or cold, tone can increase artificially, so try to standardize the testing environment. Document which muscle groups you tested and the position used so future assessments match.
It also helps to test the unaffected side first when possible. This gives you a baseline for what that patient’s normal resistance feels like, making increased tone on the affected side easier to detect.
Reliability of the Scale
When the same examiner tests the same patient on separate occasions, reliability is generally strong. A study of stroke patients across 13 muscle groups found intrarater reliability (same tester, different sessions) was good to excellent for the upper limb, with kappa values ranging from 0.71 to 0.94, and moderate to excellent for the lower limb (kappa 0.55 to 0.97).
When different examiners score the same patient, agreement drops. Interrater reliability was poor to good for the upper limb (kappa 0.25 to 0.66) and moderate for the lower limb (kappa 0.41 to 0.54). The highest agreement between examiners was found for the shoulder adductors and the soleus muscle. This means the MAS is most useful when the same clinician performs repeated assessments on a patient over time, rather than comparing scores between different clinicians.
What Counts as a Meaningful Change
Not every change in score reflects a real clinical difference. Research on stroke patients has established minimal clinically important difference (MCID) values for the MAS. For upper extremity muscles, an average change of about 0.5 points represents a moderate meaningful improvement, while a change of roughly 0.8 points reflects a large one. For lower extremity muscles, those thresholds are similar: approximately 0.45 and 0.73 points, respectively. The scale has been shown to be markedly responsive in detecting changes in muscle tone after treatment, with standardized response means between 0.89 and 1.09.
In practical terms, if you’re tracking a patient through a course of spasticity management and their average MAS score drops by half a point or more across the tested muscles, that likely represents a real and meaningful reduction in tone.
Limitations to Keep in Mind
The MAS is subjective. What you feel as resistance depends on your experience, hand sensitivity, and how consistently you move the limb. The scale also cannot distinguish between resistance caused by neural spasticity (overactive stretch reflexes) and resistance caused by soft tissue changes like contracture or fibrosis. A stiff joint from months of immobility will score high on the MAS even if the nervous system isn’t driving the resistance. This means a high score doesn’t automatically confirm spasticity in the neurological sense.
The scale also lacks true velocity standardization. The instruction to move “over one second” is a guideline, not a precise measurement. Faster movements will provoke more spasticity, and slower movements will provoke less, which introduces variability. For research or situations where precise measurement matters, instrumented tools like the Tardieu Scale or isokinetic dynamometry may provide more nuanced data. For routine clinical assessment and tracking changes within a single clinician’s caseload, the MAS remains practical and widely accepted.