Objective. To determine the natural variability and symmetry of force platf
orm parameters in normal and cerebral palsy gait.
Design. Force platform data has been analysed using coefficient of variatio
n, analysis of variances and symmetry index.
Background. It is important to establish the natural variability of force p
latform data so that changes in gait due to natural variability and those d
ue to intervention can be determined.
Methods. Force platform data and walking speed were recorded in 15 normal v
olunteers and 11 children with cerebral palsy on 3 consecutive days. Five r
ecordings were made of each leg on each day.
Results. The force platform parameters in both groups showed greater asymme
try in the horizontal plane. In the cerebral palsy group significant asymme
try was found in all 3 directions. The variation of the vertical ground rea
ction force peaks (Fz(1) and Fz(3)) and of the anterior-posterior negative
peak (Fy(3)) for both groups was low. Fz(3) was the most reproducible force
parameter. The other force parameters showed high variability and are not
considered reliable measures of gait. The temporal parameters and the walki
ng speed were reproducible measures.
Conclusions. Only selected ground reaction force parameters showed acceptab
le stability and reproducibility. Therefore caution has to be taken in the
selection of these parameters. when assessing the effects of any interventi
on on cerebral palsy gait.