Modified Ashworth Scale

Abstract

The Modified Ashworth Scale (MAS) is a widely utilized clinical tool designed to objectively assess the degree of spasticity in patients suffering from central nervous system lesions. The MAS primarily quantifies the level of hypertonia, specifically by measuring resistance encountered during rapid, standardized passive movement of specific joints.

Assessments are typically focused on major joints, such as the left and right elbow and knee. The clinician rates the muscle tone based on the resistance felt over five repetitions per joint area, utilizing a 6-point ordinal scale ranging from 0 (no increase in muscle tone) to 4 (limb rigid in flexion or extension, meaning it cannot be moved).

Keywords

Modified Ashworth Scale, MAS, spasticity, hypertonia, muscle tone, physical therapy, neurological assessment, rehabilitation.

Authors

Bohannon RW, Smith MB (1987); Dutch Version: de Jong K, Sanderink T, Heesbeen I (2001).

Purpose

The primary purpose of the MAS is to provide a quick, simple, and clinically practical method for grading the severity of muscle spasticity. It serves as a fundamental screening tool in clinical settings to monitor changes in tone over time, particularly in response to pharmacological, surgical, or physical therapy interventions aimed at reducing hypertonia.

It is specifically employed to measure the resistance to rapid, passive stretch in key muscle groups, providing a quantitative score that assists clinicians in developing appropriate treatment plans for individuals with neurological deficits, such as those resulting from stroke, multiple sclerosis, or spinal cord injury. The assessment focuses on both the upper extremity and lower extremity.

Construct

The central construct measured by the MAS is muscle tone, specifically focusing on the pathological increase in tone known as hypertonia or spasticity. Spasticity is defined as a velocity-dependent increase in tonic stretch reflexes resulting from hyperexcitability of the stretch reflex, often a component of the Upper Motor Neuron Syndrome.

The scale operationalizes this construct by measuring the resistance felt by the examiner during an imposed, rapid stretch maneuver. A higher score reflects greater resistance, which is interpreted as a higher degree of spasticity affecting the mobility and function of the extremities.

Validity

The validity of the MAS has been a subject of extensive research due to its subjective nature. Early studies indicated questionable construct validity, particularly when attempting to correlate MAS scores directly with electrophysiological measures of reflex hyperexcitability. However, the scale demonstrates adequate face validity as a measure of resistance to passive movement, which is a key clinical manifestation of spasticity.

Concurrent validity has shown mixed results. While some research supports correlation between MAS scores and quantitative biomechanical measures (e.g., torque measurements), others suggest that the MAS primarily measures overall stiffness rather than the specific, velocity-dependent component of true spasticity. Its utility is generally accepted in tracking patient status over time within a clinical setting, provided the same rater is used consistently.

Reliability

The Reliability of the MAS, particularly its inter-rater Reliability (consistency between different raters), is often cited as a significant limitation. Studies have shown that inter-rater reliability can range from poor to moderate, depending on the joint tested, the patient population, and the training of the assessors. However, intra-rater Reliability (consistency of the same rater) is generally reported as good to excellent.

The 1987 modification by Bohannon and Smith, which introduced the 6-point ordinal scale (0 to 4, with 1+), was an attempt to improve the reliability of the original Ashworth Scale. Despite ongoing debates, the MAS remains widely used because it is non-invasive, quick, and requires no specialized equipment, making it highly practical for routine clinical assessment.

Factor Analysis

As the Modified Ashworth Scale is a single-item, observational rating applied separately to various joints and muscle groups, it does not typically undergo traditional psychometric factor analysis designed for multi-item questionnaires. The score assigned (0–4) is a direct measure of the observed resistance rather than a latent factor derived from multiple questions.

However, when considered across multiple joints (e.g., bilateral elbow and knee scores), researchers may analyze correlations to determine if spasticity presents as a unitary phenomenon across the body. Clinically, the MAS operates on the assumption of a single underlying construct, hypertonia, manifesting locally at the assessed joint.

Instrument

Test Type: Observational Clinical Assessment

Format: 6-point Ordinal Scale (0, 1, 1+, 2, 3, 4)

Language Available: English (Original), Dutch, and widely used internationally.

Population Group: Patients presenting with neurological conditions resulting in spasticity (Nervous system and senses).

Age Group: Children, Adults, Elderly

Population Details: Individuals diagnosed with conditions such as stroke (CVA), multiple sclerosis, cerebral palsy, traumatic brain injury, and spinal cord injury.

Test Methodology: The therapist performs five rapid, passive stretches on the specified limb segment (upper extremity or lower extremity). The highest level of resistance encountered during the movement is recorded as the score.

Keywords

Neurology, stroke, cerebral palsy, muscle stiffness, assessment scale, physical examination, rehabilitation outcome measure.

Authors

Author ORCID Identifier: Not specified in source.

Affiliation Email addresses: Not specified in source.

Correspondence Address: Not specified in source.

Permissions & Fee and Test Year

The Modified Ashworth Scale is a non-proprietary, public domain clinical measure. There are generally no fees or permissions required for its use in research or clinical practice.

The original Ashworth Scale was developed by Ashworth in 1964. The critical modification (MAS) used today was published by Bohannon RW and Smith MB in 1987. The Dutch version was established in 2001.

Reference’s

• Bohannon, R. W., & Smith, M. B. (1987). Interrater reliability of a modified Ashworth scale of muscle spasticity. Physical Therapy, 67(2), 206-207.
• Ashworth, B. (1964). Preliminary trial of carisoprodol in multiple sclerosis. Practitioner, 192, 540-542.
• De Jong, K., Sanderink, T., & Heesbeen, I. (2001). Nederlandse vertaling en handleiding van de Modified Ashworth Scale. [Dutch translation and manual of the Modified Ashworth Scale].

The original PDF documentation for the explanation form can be downloaded here: MAS Explanation Form (PDF).

The original PDF documentation for the measurement instrument can be downloaded here: MAS Measurement Instrument (PDF).

Items of the Modified Ashworth Scale

IMPORTANT: The following scale items must be preserved in their original language and must not be changed in any way.

The MAS uses a 6-point scale (scores 0 to 4):

1. 0 = Geen verhoogde spiertonus.
2. 1 = Lichte verhoogde spiertonus, zich uitend in een ‘catch’ en ‘release’ of minimale weerstand aan het einde van de bewegingsuitslag wanneer het aangedane segment in flexie of extensie wordt bewogen.
3. 1+ = Lichte verhoogde spiertonus, zich uitend in een ‘catch’, gevolgd door minimale weerstand gedurende de rest van de bewegingsuitslag (minder dan de helft).
4. 2 = Duidelijke toename van de spiertonus, maar het aangedane deel kan gemakkelijk worden bewogen.
5. 3 = Aanzienlijke toename van de spiertonus; passieve beweging is moeilijk.
6. 4 = Het aangedane deel is rigide in flexie of extensie.