Gross Motor Function Measure

Abstract

The Gross Motor Function Measure (GMFM) is a standardized, observational clinical measure specifically designed to evaluate changes in gross motor function over time in children, particularly those diagnosed with cerebral palsy (CP). Developed initially by Russell et al. in 1990 (GMFM-88), the measure assesses how much of an activity a child can perform, rather than the quality of the movement. The GMFM-88 version comprises 88 items grouped into five distinct dimensions (Lying and Rolling, Sitting, Kneeling and Crawling, Standing, and Walking, Running, and Jumping), with each item scored on a four-point ordinal scale ranging from 0 (does not initiate) to 3 (completes the activity).

Keywords

Gross Motor Function Measure, GMFM-88, Cerebral Palsy, pediatric assessment, functional mobility, observational scale, psychometric properties, physical therapy.

Authors

Russell DJ, Rosenbaum PL, Avery LM, Lane M (Primary development, 1998); Ketelaar M, Vermeer A, Helders PJM (Dutch adaptation, 1999).

Purpose

The primary purpose of the GMFM is to measure quantitative changes in the functional gross motor skills of children with cerebral palsy. It is widely used in clinical settings and research trials to monitor progress following interventions, such as physical therapy, surgical procedures, or pharmacological treatments. The scale helps clinicians determine if a specific intervention is effective by providing an objective, standardized score of motor capability.

The GMFM is also essential for describing a child’s current level of motor performance and establishing treatment goals. While initially developed for children with CP, it has been validated and applied to other pediatric populations with movement disorders, including Down syndrome and traumatic brain injury, although its core strength remains its application to CP across various functional levels.

Construct

The GMFM measures the construct of functional gross motor performance. This construct encompasses the ability of the child to execute major bodily movements necessary for daily life, focusing on actions that involve large muscle groups. The scale is designed to measure capability (what the child can do) rather than typical performance (what the child usually does).

The GMFM-88 version is conceptually structured around five dimensions representing progressively complex motor tasks, aligning with typical developmental milestones. These dimensions capture movements from basic foundational skills (lying and rolling) to advanced locomotive skills (walking, running, and jumping). The GMFM is not intended to measure quality of movement, but rather the degree of successful completion of the task.

Validity

The GMFM demonstrates strong evidence of validity across multiple domains. Content validity is high, as the 88 items were derived from extensive clinical input and literature review, covering the full range of motor function seen in children with CP. The items are ordered by difficulty, reflecting developmental progression.

Construct validity is supported by its strong correlation with other measures of motor function and disability, such as the Pediatric Evaluation of Disability Inventory (PEDI) and the Gross Motor Function Classification System (GMFCS). The scale exhibits known-groups validity, successfully distinguishing between children classified at different levels of the GMFCS, with higher GMFM scores corresponding to lower GMFCS levels (better function).

Reliability

The GMFM possesses excellent reliability, which is critical for a measure used to track changes over time. Inter-rater reliability (consistency between different assessors) and intra-rater reliability (consistency of the same assessor over time) are reported as very high, typically exceeding intraclass correlation coefficients (ICCs) of 0.90 for total scores, provided raters are properly trained.

Test-retest reliability has also been established, confirming that the measure provides stable scores when administered to the same child under stable conditions over a short period. The internal consistency of the GMFM-88, assessed using Cronbach’s alpha, is consistently reported above 0.95, indicating that the items within the total scale reliably measure the same underlying construct of gross motor function.

Factor Analysis

Initial factor analysis of the GMFM-88 confirmed the intended five-dimensional structure, reflecting the hierarchical nature of gross motor skill development. However, subsequent research utilizing Rasch analysis led to the development of the shorter 66-item version (GMFM-66).

The GMFM-66 uses Item Response Theory (IRT) principles, specifically the Rasch model, which suggests that the 66 items measure a single, unidimensional construct of gross motor ability. This refinement allows for interval-level measurement and score conversion that accounts for item difficulty, making the GMFM-66 statistically superior for detecting small but clinically meaningful changes, particularly in research settings.

Instrument

Test Type: Observational performance measure

Format: Standardized observational scale administered by a trained clinician or therapist.

Language Available: Original English; validated Dutch version available (Ketelaar M, et al., 1999), and numerous other translations worldwide.

Population Group: Children.

Age Group: Typically 5 months to 16 years, depending on the child’s motor ability level.

Population Details: Primarily children diagnosed with cerebral palsy, classified across all levels of the GMFCS. Also applicable to other pediatric neuromuscular conditions.

Test Methodology: The child is asked to perform specific motor tasks. The assessor records the degree of completion for each task using a 4-point ordinal scale (0=cannot initiate, 3=completes the task). Scoring requires minimal or no assistance from the therapist. The assessment usually takes 45 to 60 minutes to administer.

Keywords

Pediatric physical therapy, measurement instrument, functional assessment, GMFM-66, mobility, developmental scale, outcome measure, Rasch analysis.

Authors

Author ORCID Identifier: N/A (Information not provided in source.)

Affiliation Email addresses: N/A (Information not provided in source.)

Correspondence Address: N/A (Information not provided in source.)

Permissions & Fee and Test Year

The GMFM was first published in its 88-item format in 1990, with the definitive publication by Russell et al. in 1998. The Dutch version was adapted in 1999. Usage often requires purchase of the manual and scoring forms from the copyright holders (usually CanChild Centre for Childhood Disability Research). Specific licensing fees may apply for commercial or large-scale research use.

The original PDF documentation for the explanatory form (Toelichtingsformulier) can be downloaded here: GMFM-form.pdf

The original PDF documentation for the measurement instrument (Meetinstrument) can be downloaded here: GMFM-meetinstr.pdf

Reference’s

• Russell, D. J., Rosenbaum, P. L., Avery, L. M., & Lane, M. (1998). Gross Motor Function Measure (GMFM-88) Manual. CanChild Centre for Childhood Disability Research.
• Ketelaar, M., Vermeer, A., & Helders, P. J. M. (1999). Functional motor abilities of children with cerebral palsy: A systematic review of the reliability and validity of the Gross Motor Function Measure (GMFM). Developmental Medicine & Child Neurology, 41(4), 273-279.
• Russell, D. J., Rosenbaum, P. L., Wright, V., Avery, L. M., & Lane, M. (2002). The Gross Motor Function Measure: a preliminary framework for interpreting change. Developmental Medicine & Child Neurology, 44(6), 405-412.

Items of the Gross Motor Function Measure

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

The GMFM-88 is structured around five dimensions that categorize 88 individual motor tasks. The scoring uses an ordinal scale ranging from 0 to 3:

• 0 = Does not initiate the activity (or completes less than 5% of the task).
• 1 = Initiates the activity (completes 5% to less than 50% of the task).
• 2 = Partially completes the activity (completes 50% to less than 100% of the task).
• 3 = Completes the activity (100% of the task).

The five dimensions (A-E) are:

• A = liggen en rollen (Lying and rolling)
• B = zitten (Sitting)
• C = knielen en kruipen (Kneeling and crawling)
• D = staan (Standing)
• E = lopen, rennen en springen (Walking, running, and jumping)