Fig. 3.

Effect of walking speed on the relative errors in a step duration, b CAD and c step length estimations. The empty shaded circles (n) represent the relative error for each walking bout when the selected algorithms are used (ICD_A for all cohorts in blue; CAD_B for the congestive heart failure (CHF), chronic obstructive pulmonary disease (COPD), healthy adults (HA), multiple sclerosis (MS) and Parkinson’s disease (PD) cohorts in red; CAD_C for the proximal femoral fracture (PFF) cohort in blue; SL_A for CHF, COPD, HA, PFF and PD in blue; and SL_B for MS in red). The filled circles indicate the median relative errors quantified in consecutive walking speed (ws) windows of 0.05 m/s. The sizes of the filled circles have been calculated as the ratio between the number of empty shaded circles in a given walking speed window and the total number of empty shaded circles (i.e., all observations). The obtained exponential curves (represented in blue and red continuous lines) and equations are the result of a best-fit approach used to determine the association between walking speed and the calculated median errors; R² values are also shown. The horizontal black dash-dotted lines visually indicate the relative error thresholds of 10 and 20%