Sit-stand and stand-sit transitions in older adults and patients with Parkinson's disease: event detection based on motion sensors versus force plates

Abstract

Background: Motion sensors offer the possibility to obtain spatiotemporal measures of mobility-related activities such as sit-stand and stand-sit transitions. However, the application of new sensor-based methods for assessing sit-stand-sit performance requires the detection of crucial events such as seat on/off in the sensor-based data. Therefore, the aim of this study was to evaluate the agreement of detecting sit-stand and stand-sit events based on a novel body-fixed-sensor method with a force-plate based analysis.

Methods: Twelve older adults and 10 patients with mild to moderate Parkinson's disease with mean age of 70 years performed sit-stand-sit movements while trunk movements were measured with a sensor-unit at vertebrae L2-L4 and reaction forces were measured with separate force plates below the feet and chair. Movement onsets and ends were determined. In addition, seat off and seat on were determined based on forces acting on the chair. Data analysis focused on the agreement of the timing of sit-stand and stand-sit events as detected by the two methods.

Results: For the start and end of standing-up, only small delays existed for the start of forward trunk rotation and end of backward trunk rotation compared to movement onset/end as detected in the force-plate data. The end of forward trunk rotation had a small and consistent delay compared to seat off, whereas during sitting-down, the end of forward trunk rotation occurred earlier in relation to seat on. In detecting the end of sitting-down, backward trunk rotation ended after reaching the minimum in the below-feet vertical force signal. Since only small time differences existed between the two methods for detecting the start of sitting-down, longer movement durations were found for the sensor-based method. Relative agreement between the two methods in assessing movement duration was high (i.e. ICCs ≥ 0.75), except for duration of standing-up in the Parkinson's patients (ICC = 0.61).

Conclusions: This study demonstrated high agreement of body-fixed-sensor based detection of sit-stand and stand-sit events with that based on force plates in older adults and patients with mild to moderate Parkinson's disease. Further development and testing is needed to establish reliability for unstandardized performance in clinical and home settings.

Figure 1

Event detection in sit-stand-sit transitions. a Trunk angle in the sagittal plane and events T1-T6 for a sit-stand-sit movement performed with arms crossed in front of the trunk by an older subject. b Vertical force signal below feet (black, solid line) and chair (grey, dashed line) and events t1-t6 for the same sit-stand-sit movement. See section ‘data analysis’ for a description of the events.

Figure 2

Movement durations estimated from body-fixed-sensor (BFS) data are plotted against those estimated from force-plate data.

Figure 3

Bland-Altman plots showing the differences in movement duration between the body-fixed-sensor (BFS) and force-plate method. a-d A reference line (solid) for the mean of difference between the two methods, lines for plus (upper, dashed) and minus (lower, dashed) 1.96 times the standard deviation of differences, and a linear trend line with the coefficient of determination (R²) are given.

Figure 4

Time differences between body-fixed-sensor (T) and force-plate (t) method for detecting sit-stand-sit events (1–6). a-b Older subjects (white boxes), patients with PD (grey boxes). Boxes denote median value, first and third quartile and whiskers denote minimum and maximum value.