Estimating mechanical cost in subjects with myelomeningocele.

An attempt was made to validate a system of calculating mechanical cost using 3-D motion analysis by using Oxygen cost measurements in 26 subjects with myelomeningocele. The three models investigated were (i) vertical excursion of the centre of mass (model 1), (ii) external work done by the centre of mass (CM) (model 2) and (iii) a full body model allowing energy transfers between segments within limbs (model 3). Oxygen cost, and models 1 and 3 all demonstrated significant differences between S1 and L4/L5 level involvement (P=0.001, 0.002 and 0.01, respectively). No significant differences were observed between subjects who had L4 and L5 level involvement. While further analysis showed a moderate correlation between Oxygen cost and the vertical excursion of CM model (R2=0.60), a lack of correlation for the more sophisticated models 2 and 3 questions their use as a method of assessing the energy cost of locomotion in this population.