1st Joint ESMAC-GCMAS Meeting - Análise de Marcha

O-45
ASSESSING THE REGULATORY ACTIVITY OF THE PARETIC LEG IN BALANCE
CONTROL
Van Asseldonk, Edwin H. F., M.Sc 1 , Buurke, Jaap H., PhD 2,3 , Renzenbrink, Gerbert. J. PhD, 2,3 ,
Van der Helm, Frans C.T. PhD 1,4 , Van der Kooij, Herman, PhD 1
1 Institute for Biomedical Technology (BMTI), Dept of Biomechanical Engineering, Enschede.
The Netherlands
2 Roessingh Research and Development, Enschede, The Netherlands
3 Roessingh Rehabilitation Centre, Enschede, The Netherlands
4 Man-Machine Systems & Control group Biomedical Engineering Group, Delft University of
Technology, Delft, The Netherlands
Summary/conclusions
We measured the regulating activity of the paretic leg during quiet stance and perturbations,
using CoP movements and ankle torques. We showed that the contribution of the paretic leg
assessed during quiet stance, either based on torques or CoP movements, overestimates the
contribution during perturbations, especially in the patients with a clear asymmetric weight
distribution.
Introduction
When studying the impact of pathology on balance control, Centre of Pressure (CoP)
movements obtained during quiet stance are often used to quantify the regulating activity of the
paretic and non-paretic leg. The Centre of Pressure is assumed to reflect the generated ankle
torque and as such the generated regulating activity [1]. However, apart of the CoP, also the
magnitude and direction of the ground reaction force is an important factor in the calculation of
the ankle torque. For pathologies which are characterized by an asymmetry in weight bearing,
like stroke, ignoring the ground reaction force might lead to overestimation of the regulating
activity. Furthermore, Van der Kooij et al. [2] showed that balance perturbations are necessary
in a closed-loop control system in order to distinguish between control activity that truly
restores balance and activity which is the consequence of sensory and motor noise.
Statement of clinical significance
For the evaluation of treatments and assessment of the impairments in balance control one
needs appropriate descriptors of the regulating activity in the paretic leg. This study compared
three different methods to calculate the regulating activity in the paretic leg of stroke patients.
Methods
Nine chronic stroke patients participated in the study. Balance responses were studied during
quiet stance and during continuous quasi-random platform movements in forward-backward
direction. We recorded body motion and ground reaction forces below each foot to calculate
the CoP movements, ankle torques and body sway. The regulating activity was calculated in
three different ways. To be able to make a comparison we quantified the paretic regulating
activity with respect to the total generated activity. The first two measures were obtained from
quiet stance data. First, the Static Balance Contribution based on CoP (SBCCoP) was
determined by dividing the root mean square of the CoP velocity (RMSVCoP) of the paretic leg
by the sum of the RMSVCoP of the paretic and non-paretic leg. Second, the Static Balance
Contribution based on ankle torques (SBCTorque) was determined by using the derivative of the
ankle torque, calculated from the ground reaction force vector instead of the CoP velocity in
the preceding calculation. The third measure was derived from the data of the platform
perturbations. The dynamic balance contribution (DBC) [3] of the paretic leg was determined
by using a system identification technique to relate the generated ankle torque to the sway
movements obtained during quasi-random platform perturbations. By using closed-loop system
- 158 -