Description

The Modified Ashworth Scale (MAS) is one of the most widely used standardized clinical instruments for assessing spasticity, defined as the abnormal increase in muscle tone resulting from lesions of the upper motor neuron. The scale is extensively employed in the evaluation of individuals with stroke, multiple sclerosis, spinal cord injury, traumatic brain injury, cerebral palsy, and other neurological disorders characterized by increased muscle tone. It serves as an essential outcome measure in neurology, physical therapy, occupational therapy, and rehabilitation medicine, providing clinicians with a simple, rapid, and reliable method for quantifying muscle spasticity and monitoring changes over time.

The MAS evaluates the resistance encountered during passive movement of a joint at a constant speed, allowing clinicians to estimate the severity of spasticity and its impact on motor performance.

The scale assesses several important aspects of neuromuscular function, including:

  • Muscle Tone – the degree of abnormal increase in resistance during passive movement.
  • Resistance to Passive Movement – the primary criterion used for grading spasticity.
  • Distribution of Resistance Throughout the Range of Motion – whether resistance occurs at the end, through part, or throughout the movement.
  • Functional Consequences of Spasticity – the influence of increased muscle tone on mobility, gait, and activities of daily living.
  • Response to Therapeutic Interventions – changes in spasticity following pharmacological treatment, physical therapy, occupational therapy, botulinum toxin injections, or other rehabilitation strategies.

The theoretical foundation of the MAS is based on Lance’s definition of spasticity, which describes it as a velocity-dependent increase in tonic stretch reflexes resulting from upper motor neuron lesions.

Analysis and Use of Data

The MAS provides clinicians and researchers with an objective method for quantifying the severity of spasticity and evaluating treatment outcomes in neurological rehabilitation. It is extensively used in both clinical practice and research involving motor disorders.

Statistical analyses commonly include:

  • Descriptive statistics (means, standard deviations, medians, and percentile distributions).
  • Reliability assessment, including inter-rater reliability and test–retest reliability.
  • Internal consistency assessment using Cronbach’s alpha and McDonald’s Omega when appropriate in research settings.
  • Construct validity evaluation through Exploratory Factor Analysis (EFA) and Confirmatory Factor Analysis (CFA) where applicable.
  • Assessment of convergent validity using instruments such as the Modified Tardieu Scale (MTS), Fugl-Meyer Assessment (FMA), Barthel Index, Functional Independence Measure (FIM), and other measures of motor function.
  • Correlation analyses using Pearson’s or Spearman’s correlation coefficients.
  • Group comparisons using independent-samples t-tests, ANOVA, ANCOVA, or appropriate non-parametric procedures.
  • Pre- and post-intervention analyses to evaluate treatment effectiveness.
  • Multivariate regression analyses to identify predictors of spasticity severity and rehabilitation outcomes.

The MAS is widely applied in:

  • Neurology
  • Physical therapy
  • Occupational therapy
  • Rehabilitation medicine
  • Pediatric neurorehabilitation
  • Clinical rehabilitation research
  • Stroke rehabilitation
  • Motor function assessment

Objective

The primary objective of the Modified Ashworth Scale (MAS) is to provide a reliable and objective assessment of the presence and severity of muscle spasticity and to monitor changes throughout the rehabilitation process. The instrument assists healthcare professionals in documenting clinical status, planning individualized rehabilitation programs, and evaluating the effectiveness of therapeutic interventions.

More specifically, the scale aims to:

  • Assess the presence and severity of muscle spasticity.
  • Quantify resistance during passive joint movement.
  • Monitor response to pharmacological and rehabilitation interventions.
  • Evaluate the effectiveness of physical and occupational therapy.
  • Assist in individualized rehabilitation planning.
  • Support evidence-based clinical decision-making.
  • Facilitate research on neurological rehabilitation and motor disorders.

Scoring

The Modified Ashworth Scale is administered by passively moving the patient’s joint through its range of motion at a standardized speed while assessing the resistance generated by the muscle. The examiner assigns one of six grades based on the observed resistance:

  • 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.
  • 1+: Slight increase in muscle tone, manifested by a catch followed by minimal resistance through less than half of the remaining range of motion.
  • 2: More marked increase in muscle tone through most of the range of motion, but the affected part is easily moved.
  • 3: Considerable increase in muscle tone, making passive movement difficult.
  • 4: The affected part is rigid in flexion or extension.

Higher scores indicate greater muscle spasticity, increased resistance to passive movement, and more severe functional impairment.

Psychometric evaluation of the MAS commonly includes:

  • Inter-rater reliability
  • Test–retest reliability
  • Convergent validity with other spasticity measures
  • Sensitivity to clinical changes following treatment
  • Criterion validity across neurological populations

References

Ansari, N. N., Naghdi, S., Arab, T. K., & Jalaie, S. (2008). The interrater and intrarater reliability of the Modified Ashworth Scale in the assessment of muscle spasticity. NeuroRehabilitation, 23(1), 31–35.

Ashworth, B. (1964). Preliminary trial of carisoprodol in multiple sclerosis. Practitioner, 192, 540–542.

Bohannon, R. W., & Smith, M. B. (1987). Interrater reliability of a modified Ashworth scale of muscle spasticity. Physical Therapy, 67(2), 206–207. https://doi.org/10.1093/ptj/67.2.206

Lance, J. W. (1980). The control of muscle tone, reflexes, and movement: Robert Wartenberg’s 1979 Lecture. Advances in Neurology, 26, 185–204.

Pandyan, A. D., Johnson, G. R., Price, C. I. M., Curless, R. H., Barnes, M. P., & Rodgers, H. (1999). A review of the properties and limitations of the Ashworth and Modified Ashworth Scales as measures of spasticity. Clinical Rehabilitation, 13(5), 373–383.