Introduction: Gait initiation is a sequence of stereotypical postural shifts culminating in a forward step. Muscular and gravitational forces interact leading to appropriate dynamic conditions that allow progression. This requires a complicated system of neural and muscular control. Derangement of ground reaction forces during gait initiation may be a more specific indicator of neuromuscular disease than steady state gait.

Little work has been done on gait initiation in children and there is no published data on gait initiation with cerebral palsy. The aim of this study was to examine the ground reaction forces and centre of pressure in normal children during gait initiation, to compare these to similar values in hemiplegic children and to try to identify differences between the two which may be diagnostic for hemiplegia.

Patients and methods: Five normal and five hemiplegic children were studied. Kinematic and dynamic data were collected using a CodaTM motion analysis system and KestlerTM force plate. All subjects stood with one foot on and one foot off the force plate and walked off upon hearing an audible cue. Tests were repeated measuring right and left, normal and hemiplegic legs as both stance and swing legs. Ground reaction forces in the X,Y and Z axes, centre of pressure and kinematic data were collected and studied.

Results: 1) Normal children. In the vertical direction for the stance leg there is an initial fall in GRF, followed by a bimodal peak in GRF. In the fore-aft direction the GRF is initially directed backwards and subsequently has a bimodal forward force.

Medio-laterally the stance GRF tending to adduct falls initially and subsequently rises with a bimodal peak. The forces in the swing leg reciprocate these forces.

2) Hemiplegic children. The overall pattern seen when the normal leg is the stance leg are similar to those in normal children with certain specific variations in force development and magnitude. When the hemiplegic leg is the stance leg the overall patterns are again similar but considerably less smooth with characteristic changes indicative of neuro-muscular disturbance. The initial “adjusting” forces tend to be larger indicating the greater force required for control.

Discussion: The pattern and relative magnitude of forces measured for normal children are identical to those previously reported for adults. This validates our study design and indicates that central programming for gait initiation develops early in life. It is therefore an early developmental skill and may be used as a diagnostic test in childhood. Significant variations are seen in cerebral palsy. Knowledge of these specific changes may allow earlier and more accurate diagnosis of cerebral palsy in children under investigation for movement disorders. Normal GRF patterns during gait initiations may provide early reassurance for parents of children suspected of having cerebral palsy.