Figure 1. Model to identify a cut-off value of Energy Cost of walk (CW).

The CW is the energy cost per kilogram per unit of distance covered (mlO₂*Kg⁻¹*min⁻¹ ). C is the criterion. J = sensitivity (C)+specificity (C). J finding the best cut-off point that is equivalent to measuring the J of Youden Index. Youden Index is the greatest vertical distance between ROC curve and the diagonal line.