Gross Motor Function Measure (GMFM)

Therapists use the GMFM to:

• Monitor a child’s development
• Assist with goal setting and planning therapy
• Evaluate the outcome of motor interventions and therapies
• Assist with predicting motor outcomes at older ages, using Motor Growth Curves² (GMFM-66 version only – see below).

The assessments are most appropriate for children aged five-months- to 16-years and can be used to assess a child with any level of motor severity.

In this assessment, a physiotherapist will ask the child with cerebral palsy to complete a number of gross motor activities, depending on the child’s age and ability. These activities could include rolling, sitting, walking backwards, climbing stairs, and standing on one foot.

The GMFM takes roughly 45 to 60 minutes to complete.

You can ask your health care provider about how the GMFM will be included within your fees for ongoing assessment and intervention.

Check with your health care provider if you are eligible for funding to assist with the assessment and intervention fees. People with disability living in Australia may also be eligible for a health care rebate through Medicare or funding from the National Disability Insurance Scheme.

Training

The GMFM is administered by a physiotherapist who is skilled at assessing the motor skills of children with cerebral palsy. They should be familiar with the GMFM test manual and have practiced using this assessment with children¹.

Cost

The GMFM manual can be purchased from the publisher, Wiley.

Forms to record the assessment can be downloaded at CanChild.

Method

The GMFM is completed in a standardised environment according to the instructions outlined in the GMFM manual. The manual also lists the materials needed to administer the assessment – items like stairs, benches and mats. The environmental conditions must be as similar as possible each time an assessment is completed with a child, to limit the effect of any changes in environment on the scores.

Each item is scored on a four-point scale¹. When using the GMFM-88, the test manual is used to give a summary score for each of the dimensions (for example, dimension B – sitting). When using the GMFM-66, the Gross Motor Ability Estimator (GMAE) is used to convert the raw scores from the assessment into an overall score.

Things to note

The GMFM is a criterion-referenced observational assessment. There are two versions – GMFM-66 and GMFM-88. Both are widely used. The GMFM-66 is the most recent version and is a subset of the original GMFM-88. It has the same level of detail and ability to detect changes in gross motor function over time, but it is shorter than the GMFM-88.

There are several differences between the versions. The GMFM-88, which has 88 items, provides scores for each dimension, whereas the GMFM-66, with 66 items, provides a total score. The GMFM-66 is only used with children who have cerebral palsy, while the GMFM-88 can also be used with children who have Down Syndrome.

Shortened versions of GMFM-66 have also been developed. The shortened versions of GMFM-66 are called GMFM-66 Items Sets (IS)³ and GMFM- 66 Basal and Ceiling (B&C)^3,4. When using these assessments, a smaller sample of GMFM-66 items are completed and scores are derived by using the Gross Motor Ability Estimator (GMAE)⁴. Both tests accurately estimate GMFM-66 scores at a single time, but GMFM-66 (IS)⁴ is the preferred shortened measure for unilateral (hemiplegic) cerebral palsy⁴. The full GMFM-66⁴ is required if the aim of assessment is to measure change.

For more information on the different versions, see the childhood disability research website CanChild.

In addition, two related measures of gross motor ability are also available:

• Challenge Module – this tests the more advanced motor skills of children with cerebral palsy, who are six-years-old and over and able to walk without devices
• Quality Function Measure – this evaluates quality of movement in standing and walking for school-aged children with cerebral palsy.

Psychometric properties reviewed

Validity – research suggests that both the GMFM-66 and GMFM-88 have good longitudinal construct validity. That is, over time, the assessments measure what they aim to measure⁵.

Reliability – test-retest reliability of both versions of the GMFM is high (intraclass correlation coefficients = 0.99 and 0.99 respectively)⁶. This means the scores obtained from the tool on consecutive occasions remain stable.

Responsiveness – research in this area indicates both versions of the GMFM adequately measure change over time in gross motor function for children with cerebral palsy^7,8. However, the GMFM-88 appears to be more sensitive to change than the GMFM-66, but this shorter version is more accurate. In particular, the GMFM-66 shows a higher specificity at all GMFCS levels, meaning that it identifies children with gross motor difficulties more accurately. Likewise, in studies which assessed the GMFM-88 and GMFM-66 in comparison to scores from the child’s treating therapists, the GMFM-66 appeared to be more closely aligned with therapists’ scores⁸.