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 and CanChild, based on work with children receiving physical therapy at the Chedoke-McMaster Hospital in Hamilton, Ontario. It was 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

Items the child cannot attempt are recorded using the separate "Not tested" category rather than simply scored as zero. CanChild advises scoring the GMFM-88 with the Not tested category so the results can be entered into the GMAE scoring program later. The evaluator scores what the child actually does, not what they think the child could do with encouragement. Items are scored by direct observation of the child, either in a clinic or from video.

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, so a child who cannot stand or walk at all still receives a percent score based on the dimensions they can attempt.

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.

The GMFM-88 evaluates a broader range of ability, from a very young infant who can barely lift their head to a school-age child who can run and jump. The GMFM-66 is better suited for children with CP who are actively working on higher-level motor skills.

For the DMI trial, the outcome measure listed in the protocol is the GMFM-88. That choice is worth noting, because the GMFM-88 includes items across all five dimensions and therefore captures change across a wider range of ability levels than the 66-item version.

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. A child classified at Level II at age 5 is expected to remain at Level II throughout childhood. The GMFCS level does not change with therapy in most children after about age 5.

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 recommends using the GMFM-88 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 a trial-specific tool called 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-88 helps you interpret that number. A five-point change on the GMFM-88 total score may or may not be clinically meaningful depending on where your child starts. Published thresholds for meaningful change are smaller than most people expect, and they vary by GMFCS level. Oeffinger and colleagues reported that on the GMFM-66 a change of about 1.7 points represents a medium effect at GMFCS level I and 2.7 points a large one, while at level II the equivalent figures are about 1.0 and 1.5 points. Thresholds rise as motor function becomes more limited. Ask your therapist which threshold applies to your child, because a gain that looks small on paper can be a large effect at some levels.

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. Not every clinic does, and the assessment takes about 45 to 60 minutes to administer properly. A clinic that uses it is demonstrating a commitment to measuring outcomes objectively.

You can also ask for your child's GMFM-88 score to be measured before and after an intensive or a course of treatment. Video of the assessment is acceptable for scoring, so you do not necessarily need a clinic visit. That gives you a number you can compare yourself when the DMI trial publishes its results.

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, Rosenbaum PL, Avery LM, Lane M. Gross Motor Function Measure (GMFM-66 & GMFM-88) User's Manual. 2nd ed. Mac Keith Press; 2013. 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