GMFM-88: What the Gross Motor Function Measure Means

If you have read the cerebral palsy pages on this site, you have seen references to the GMFM-88 as a primary outcome measure in the completed clinical trial comparing DMI and the Bobath approach. This post explains what the GMFM-88 is, how it is scored, what it tells you, and how it differs from the GMFCS classification system.

What is the GMFM-88?

The Gross Motor Function Measure is a standardized clinical assessment designed to measure gross motor function in children with cerebral palsy. It was developed by a team led by Dianne Russell and Peter Rosenbaum at McMaster University in Hamilton, Ontario, and first published in 1989 in Developmental Medicine and Child Neurology.

The GMFM-88 contains 88 items grouped into five dimensions of motor function. The full edition is called the GMFM-88 because it contains all 88 original items. A shorter 66-item version (GMFM-66) was later developed using Rasch analysis for use specifically with children who have cerebral palsy.

The five dimensions

Each item in the GMFM-88 belongs to one of five dimensions, arranged from easiest to hardest:

How is it scored?

Each of the 88 items is scored on a four-point ordinal scale:

• 0 = does not initiate the movement
• 1 = initiates the movement (completes less than 10 percent of the item)
• 2 = partially completes the item (completes 10 to 99 percent)
• 3 = completes the item independently

A child who does not initiate an item scores 0. That is different from an item that was not tested at all, which is marked "Not tested" rather than scored. The official score sheet stresses keeping the two apart, and CanChild advises using the Not tested category so the results can later be entered into the GMFM-66 scoring program. The evaluator scores what the child actually does during the assessment, following the detailed item guidelines in the GMFM manual.

The raw scores are converted into dimension percentage scores (actual points divided by maximum points in that dimension, multiplied by 100), and the overall total score is the average of the five dimension percentages. This means each dimension contributes equally to the total regardless of how many items it contains. A child who cannot yet stand or walk scores low in those two dimensions, which pulls the total down. Clinicians can also calculate a goal total score that averages only the dimensions chosen as goal areas.

GMFM-88 versus GMFM-66

The GMFM-66 is a subset of 66 items selected through Rasch analysis to best describe gross motor function specifically in children with cerebral palsy. The GMFM-66 uses a more complex scoring method that produces interval-level scores (equal distances between points on the scale have the same meaning) rather than the ordinal-level scores of the GMFM-88.

CanChild says the GMFM-88 gives more descriptive information for very young children and for children with more complex motor disability, such as those at GMFCS level V, because it has more items describing early motor skills. It is also the version to use for children with Down syndrome, and when testing with walking aids, orthoses, or shoes, because GMFM-66 scores are based on barefoot testing. The GMFM-66 takes less time to give, and CanChild considers it the more meaningful measure of a child's change over time, because its items are ordered by difficulty.

For the DMI trial, the outcome measure listed in the trial registration is the GMFM-88.

How is the GMFM-88 different from the GMFCS?

These two measures are frequently confused because they share initials and come from the same research group, but they serve completely different purposes.

The GMFCS classifies a child into one of five stable categories (I through V) based on their self-initiated mobility in daily life. CanChild, which publishes the GMFCS, reports that levels are quite stable after 2 years of age and that children are not likely to change levels even following intervention.

The GMFM-88 produces a numerical score that can improve, stay the same, or decline over time. A child at GMFCS Level III who starts with a GMFM-88 total score of 40 percent and improves to 55 percent after an intervention has made real progress, even though their GMFCS classification has not changed.

In practice, the GMFCS tells you what category your child fits into, and the GMFM-88 tells you how their motor skills are changing within that category. Researchers use both: the GMFCS to describe who was studied, and the GMFM-88 to measure whether the intervention changed anything.

What does the GMFM-88 not tell you?

The GMFM-88 measures what a child can do in a structured assessment setting. It does not measure how often they use those skills in daily life, nor how efficiently or comfortably they move. A child who scores well on the GMFM-88 may still have difficulty keeping up with peers on the playground, may tire quickly, or may need help navigating uneven surfaces.

The GMFM-88 also does not measure fine motor skills, communication, social function, or quality of life. It is specific to gross motor function, and that limitation is important when you read study results: a change in GMFM-88 score tells you about motor change only, which is valuable but partial.

Finally, the GMFM-88 was developed and validated primarily for children with cerebral palsy. It has also been studied in children with Down syndrome, acquired brain injury, and a few other conditions, but less is known about its measurement properties in those populations. The CanChild research group at McMaster University says the GMFM-88 can be used for children with Down syndrome but considers the GMFM-66 valid only for cerebral palsy.

Why it matters for the research on this site

The completed clinical trial comparing DMI to the Bobath approach (NCT07238634) used the GMFM-88 as a primary outcome measure, alongside the Trunk Impairment Scale and the Shoaib Sensorimotor Development Tool. When the results are published, the GMFM-88 score will be one of the main numbers researchers and families will look at.

Understanding the GMFM helps you interpret that number, but there is no single cut-off for a meaningful change. The best-known published thresholds come from Oeffinger and colleagues, who followed 381 walking children aged 4 to 18 at GMFCS levels I to III. On the GMFM-66, they calculated that a change of about 1.7 points was a medium effect and 2.7 points a large one at level I, 1.0 and 1.5 points at level II, and 0.7 and 1.2 points at level III. The thresholds were smaller, not larger, for children with more limited motor function. Those figures are for the GMFM-66, not the GMFM-88 total score the DMI trial reports, and they come from older children than the trial enrolled. Ask your therapist what change would be meaningful for your child, because a gain that looks small on paper can matter.

When the trial results appear, you can look at the reported GMFM-88 scores and ask: did the change exceed what would be expected from typical development or practice alone? Was the difference between the DMI group and the Bobath group large enough to be clinically important? Those questions give you more information than a simple "did it work or not" answer.

What you can do with this information

If your child has cerebral palsy and you are considering DMI or any other gross motor intervention, ask your therapist whether they use the GMFM-88 or GMFM-66 to track progress. The GMFM-66 takes less time to give than the GMFM-88, because not every item has to be tested. Either one gives you a standardized measure rather than an impression.

You can also ask for your child's GMFM score to be measured before and after an intensive or a course of treatment. That gives you a standardized way to see how your child's gross motor function changed.

Where it appears on this site

The GMFM-88 is referenced on our cerebral palsy guide as a primary outcome measure in the completed DMI clinical trial, and it is contrasted with the GMFCS in our GMFCS explainer.

Sources

• Russell DJ, Rosenbaum PL, Cadman DT, Gowland C, Hardy S, Jarvis S. The Gross Motor Function Measure: A means to evaluate the effects of physical therapy. Developmental Medicine and Child Neurology. 1989;31(3):341-352. PubMed
• Russell DJ, Wright M, Rosenbaum PL, Avery LM. Gross Motor Function Measure (GMFM-66 & GMFM-88) User's Manual. 3rd ed. London: Mac Keith Press; 2021. CanChild
• CanChild Centre for Childhood Disability Research. FAQ's about Measures. CanChild
• Oeffinger D, Bagley A, Rogers S, et al. Outcome tools used for ambulatory children with cerebral palsy: responsiveness and minimum clinically important differences. Developmental Medicine and Child Neurology. 2008;50(12):918-925. PubMed
• CanChild Centre for Childhood Disability Research. GMFCS – Expanded & Revised (GMFCS-E&R). CanChild
• Gross Motor Function Measure (GMFM) Score Sheet (GMFM-88 and GMFM-66 scoring), CanChild, McMaster University. CanChild