Validation of a Step Detection Algorithm during Straight Walking and Turning in Patients with Parkinson's Disease and Older Adults Using an Inertial Measurement Unit at the Lower Back

Abstract

Introduction: Inertial measurement units (IMUs) positioned on various body locations allow detailed gait analysis even under unconstrained conditions. From a medical perspective, the assessment of vulnerable populations is of particular relevance, especially in the daily-life environment. Gait analysis algorithms need thorough validation, as many chronic diseases show specific and even unique gait patterns. The aim of this study was therefore to validate an acceleration-based step detection algorithm for patients with Parkinson's disease (PD) and older adults in both a lab-based and home-like environment.

Methods: In this prospective observational study, data were captured from a single 6-degrees of freedom IMU (APDM) (3DOF accelerometer and 3DOF gyroscope) worn on the lower back. Detection of heel strike (HS) and toe off (TO) on a treadmill was validated against an optoelectronic system (Vicon) (11 PD patients and 12 older adults). A second independent validation study in the home-like environment was performed against video observation (20 PD patients and 12 older adults) and included step counting during turning and non-turning, defined with a previously published algorithm.

Results: A continuous wavelet transform (cwt)-based algorithm was developed for step detection with very high agreement with the optoelectronic system. HS detection in PD patients/older adults, respectively, reached 99/99% accuracy. Similar results were obtained for TO (99/100%). In HS detection, Bland-Altman plots showed a mean difference of 0.002 s [95% confidence interval (CI) -0.09 to 0.10] between the algorithm and the optoelectronic system. The Bland-Altman plot for TO detection showed mean differences of 0.00 s (95% CI -0.12 to 0.12). In the home-like assessment, the algorithm for detection of occurrence of steps during turning reached 90% (PD patients)/90% (older adults) sensitivity, 83/88% specificity, and 88/89% accuracy. The detection of steps during non-turning phases reached 91/91% sensitivity, 90/90% specificity, and 91/91% accuracy.

Conclusion: This cwt-based algorithm for step detection measured at the lower back is in high agreement with the optoelectronic system in both PD patients and older adults. This approach and algorithm thus could provide a valuable tool for future research on home-based gait analysis in these vulnerable cohorts.

Keywords: Parkinson’s disease; accelerometer; gait analysis; home-like activities; older adults; turning.

Figure 1

Experimental setting of the lab assessment showing the inertial measurement unit (IMU) position on the lower back, and the heel and toe markers to identify heel strike and toe off using the optoelectronic motion capture system.

Figure 2

Heel strike (HS) and toe off (TO) detection using continuous wavelet transform (cwt) algorithm. IMU, inertial measurement unit; LPF, low-pass filter.

Figure 3

(A) Heel strike (HS) and toe off (TO) were detected from the anterior–posterior (AP) coordinates of the heel and toe markers (gold standard). (B) Event detection from both feet, from AP acceleration (dashed line), its first-order differential continuous wavelet transform (dcwt) (dotted line, dcwt1) and its second-order dcwt (solid line, dcwt2). Black stars indicate HS, and black circles indicate TO. Dashed and solid vertical lines enable the comparison of the two methods to detect HS and TO, showing an overall good correspondence between them.

Figure 4

(A) Bland–Altman plot illustrating the agreement for time of heel strike detection between the algorithm and the gold standard. The continuous line is the mean, and dashed lines are the 95% confidence intervals (CIs) of step observation difference (in seconds). (B) Bland–Altman plot illustrating the agreement for time of toe off detection between the algorithm and the gold standard. The continuous line represents the mean, and dashed lines are the 95% CI of step observation difference (in seconds). IMU, inertial measurement unit.