Test-retest reliability of hand-held dynamometric strength testing in young people with cerebral palsy.

Objective: To evaluate the test-retest reliability of measuring lower-limb strength with a hand-held dynamometer in young people with cerebral palsy (CP).
Design: One rater measured the isometric strength of the lower limbs in 10 participants with CP on 2 occasions separated by 6 weeks.
Setting: University movement rehabilitation laboratory in Australia.
Participants: Ten young people (mean age +/- standard deviation, 13.5+/-3.4 y) with spastic diplegic CP. Eight of the participants walked independently and 2 walked with assistive devices.
Interventions: Not applicable.
Main Outcome Measures: Retest reliability of lower-limb strength, expressed in the units of measurement for the interpretation of group mean and individual scores and as intraclass correlation coefficients (ICC(2,1)).
Results: For groups, mean lower-limb strength increases of 7 kg (30%) could be interpreted as real change using 95% confidence intervals (CIs). For individuals, for strength gains to be interpreted as real change using 95% CIs, strength increases would need to be greater than 16.8 kg (70%) for the measurement of knee extension and to be greater than 4.3 kg (25%) for ankle plantarflexion. Measurement of hip extension strength was not reliable for group mean or individual scores. All reliability coefficients were greater than.80.
Conclusion: A hand-held dynamometer can reliably measure changes in lower-limb strength for groups of young people with CP. It is uncertain whether this method is useful for evaluating change in individuals. Relying only on a coefficient of reliability to decide the usefulness of a measurement can be misleading.