Ashworth Scale / Modified Ashworth Scale (AS/MAS)

Abstract

The Ashworth Scale (AS) and its revision, the Modified Ashworth Scale (MAS), are clinical measures designed to assess the degree of muscle tone and resistance to passive movement in patients exhibiting spasticity. The original scale utilized a 5-point grading system (0 to 4), while the MAS, developed by Richard Bohannon and Melissa Smith (1987), incorporated a 1+ score to better differentiate between minimal resistance encountered early in the range of motion (ROM) and resistance present only at the end range. The MAS is widely used in rehabilitation settings, particularly for individuals with lesions of the central nervous system, such as those recovering from stroke or spinal cord injury.

Keywords

Ashworth Scale, Modified Ashworth Scale, MAS, Spasticity, Muscle Tone, Passive Movement, Physical Therapy, Rehabilitation, Central Nervous System Lesion, Range of Motion.

Authors

Richard Bohannon PT, PhD, Melissa Smith, PT.

Purpose

The primary objective of the original Ashworth Scale was pharmaceutical evaluation—specifically, to quantify the efficacy of anti-spasticity medications in patients diagnosed with Multiple Sclerosis (MS). This initial application focused on standardized measurement of resistance changes following drug intervention.

The Modified Ashworth Scale (MAS) expanded this utility and is now predominantly used as a standardized clinical tool to measure the severity of spasticity in individuals who have sustained damage to the upper motor neurons, typically resulting from conditions like stroke, traumatic brain injury, or spinal cord injury. It serves as a rapid, accessible measure for clinicians to track changes in muscle tone over time or across different treatment modalities.

Construct

The core construct measured by both the AS and MAS is hypertonia, specifically the velocity-dependent increase in muscle tone known as spasticity. It is an ordinal scale that quantifies the resistance encountered by an examiner during rapid, passive movement of a joint.

The scoring system reflects the level of resistance, ranging from no resistance (score 0) to severe rigidity (score 4). The critical addition of the 1+ category in the MAS allows for a finer distinction in mild presentations of hypertonia, separating minimal resistance that catches and releases quickly from resistance that persists throughout a larger portion of the ROM.

Validity

While the MAS is widely applied clinically, its construct validity—the extent to which it truly measures only spasticity independent of other factors like contracture or soft tissue stiffness—remains a topic of academic discussion. Generally, the scale is accepted as a reliable measure of resistance to passive movement, which is a key clinical manifestation of spasticity.

Studies often evaluate the scale’s concurrent validity by comparing MAS scores against more objective biomechanical measures (e.g., electromyography or dynamometry). However, due to its simplicity and ease of use, the MAS is primarily valued for its strong face validity and clinical utility in quick, bedside assessments within rehabilitation settings.

Reliability

Extensive psychometric evaluations, detailed in studies by Bohannon & Smith (1987), Brashear et al. (2002), and Gregson et al. (1999; 2000), primarily address the interrater reliability and intrarater reliability of the MAS. The original study by Bohannon and Smith (1987) established the interrater reliability of the MAS as acceptable, particularly when standardized testing procedures are rigorously followed.

Reliability findings can vary significantly depending on the joint tested (e.g., lower vs. upper extremities), the patient population (e.g., stroke vs. spinal cord injury), and the experience level of the examiner. For instance, Blackburn et al. (2002) specifically examined the reliability of MAS measurements in the lower extremities of stroke survivors, reinforcing its use in this population. Haas et al. (1996) also contributed significantly to the understanding of reliability in patients with spinal cord injury.

Factor Analysis

As the Ashworth Scale and the Modified Ashworth Scale are single-item, ordinal clinical rating instruments designed to assess one dimension (resistance to passive movement), they are not appropriate candidates for traditional exploratory or confirmatory factor analysis. Factor analysis is generally reserved for multi-item questionnaires designed to determine underlying latent constructs or factors.

Instrument

Test Type: Clinical Observational Rating Scale; Physical Assessment.

Format: Ordinal scale (6 points: 0, 1, 1+, 2, 3, 4) based on manual passive movement assessment.

Language Available: Non-language dependent (Physical movement assessment).

Population Group: Clinical population exhibiting hypertonia or spasticity.

Age Group: Adolescents and Adults (used widely across clinical populations, generally post-neurological event).

Population Details: Patients with lesions of the central nervous system, including stroke survivors, spinal cord injury patients, traumatic brain injury patients, and those with Multiple Sclerosis (MS).

Test Methodology: Passive movement of a joint through its full range of motion at a standardized speed (counted as “one thousand one”) to elicit and grade the resistance experienced by the examiner.

Keywords

Hypertonia, Neurological Assessment, Stroke Rehabilitation, Spine Injury, Ordinal Scale, Bohannon, Smith, Muscle Rigidity, Passive ROM.

Authors

Author ORCID Identifier: N/A

Affiliation Email addresses: N/A

Correspondence Address: N/A (Refer to original publications for current contact information for Richard Bohannon PT, PhD and Melissa Smith, PT).

Permissions & Fee and Test Year

The Modified Ashworth Scale (MAS) is a widely utilized clinical assessment tool published in 1987. It involves a physical examination technique and is generally considered to be in the public domain for clinical use and research purposes, requiring no specific license fees for administration.

Test Year (MAS): 1987 (Modification published by Bohannon & Smith).

Reference’s

Blackburn, M., van Vliet, P., et al. (2002). “Reliability of measurements obtained with the modified Ashworth scale in the lower extremities of people with stroke.” Physical Therapy 82(1): 25.

Bohannon, R. and Smith, M. (1987). “Interrater reliability of a modified Ashworth scale of muscle spasticity.” Physical Therapy 67(2): 206.

Brashear, A., Zafonte, R., et al. (2002). “Inter-and intrarater reliability of the Ashworth Scale and the Disability Assessment Scale in patients with upper-limb poststroke spasticity* 1.” Archives of physical medicine and rehabilitation 83(10): 1349-1354.

Gregson, J., Leathley, M., et al. (1999). “Reliability of the Tone Assessment Scale and the modified Ashworth scale as clinical tools for assessing poststroke spasticity.” Archives of physical medicine and rehabilitation 80(9): 1013-1016.

Gregson, J., Leathley, M., et al. (2000). “Reliability of measurement of muscle tone and muscle power in stroke patients.” Age and Ageing 29(3): 223.

Haas, B., Bergström, E., et al. (1996). “The inter rater reliability of the original and of the modified Ashworth scale for the assessment of spasticity in patients with spinal cord injury.” Spinal Cord 34(9): 560-564.

Items of the Ashworth Scale /Modified Ashworth Scale (AS/MAS)

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

Modified Ashworth Scale Instructions

General Information (derived Bohannon and Smith, 1987):

• Place the patient in a supine position
• If testing a muscle that primarily flexes a joint, place the joint in a maximally flexed position and move to a position of maximal extension over one second (count “one thousand one”)
• If testing a muscle that primarily extends a joint, place the joint in a maximally extended position and move to a position of maximal flexion over one second (count “one thousand one”)
• Score based on the classification below

Scoring (taken from Bohannon and Smith, 1987):

• 0: No increase in muscle tone
• 1: Slight increase in muscle tone, manifested by a catch and release or by minimal resistance at the end of the range of motion when the affected part(s) is moved in flexion or extension
• 1+: Slight increase in muscle tone, manifested by a catch, followed by minimal resistance throughout the remainder (less than half) of the ROM
• 2: More marked increase in muscle tone through most of the ROM, but affected part(s) easily moved
• 3: Considerable increase in muscle tone, passive movement difficult
• 4: Affected part(s) rigid in flexion or extension