Reliability of IMU-Derived Static Balance Parameters in Neurological Diseases

Abstract

Static balance is a commonly used health measure in clinical practice. Usually, static balance parameters are assessed via force plates or, more recently, with inertial measurement units (IMUs). Multiple parameters have been developed over the years to compare patient groups and understand changes over time. However, the day-to-day variability of these parameters using IMUs has not yet been tested in a neurogeriatric cohort. The aim of the study was to examine day-to-day variability of static balance parameters of five experimental conditions in a cohort of neurogeriatric patients using data extracted from a lower back-worn IMU. A group of 41 neurogeriatric participants (age: 78 ± 5 years) underwent static balance assessment on two occasions 12–24 h apart. Participants performed a side-by-side stance, a semi-tandem stance, a tandem stance on hard ground with eyes open, and a semi-tandem assessment on a soft surface with eyes open and closed for 30 s each. The intra-class correlation coefficient (two-way random, average of the k raters’ measurements, ICC2, k) and minimal detectable change at a 95% confidence level (MDC95%) were calculated for the sway area, velocity, acceleration, jerk, and frequency. Velocity, acceleration, and jerk were calculated in both anterior-posterior (AP) and medio-lateral (ML) directions. Nine to 41 participants could successfully perform the respective balance tasks. Considering all conditions, acceleration-related parameters in the AP and ML directions gave the highest ICC results. The MDC95% values for all parameters ranged from 39% to 220%, with frequency being the most consistent with values of 39–57%, followed by acceleration in the ML (43–55%) and AP direction (54–77%). The present results show moderate to poor ICC and MDC values for IMU-based static balance assessment in neurogeriatric patients. This suggests a limited reliability of these tasks and parameters, which should induce a careful selection of potential clinically relevant parameters.

Reliability of IMU-Derived Temporal Gait Parameters in Neurological Diseases

“…The systematic reliability assessment of the parameters allows to distinguish between values within the MDC range or values representing a real effect of a clinical intervention. In comparison to previously published research highlighting the day-to-variability of balance parameters [ 9 ], the gait parameters extracted in this study indicate higher relative reliability values (ICC) and lower absolute reliability values (MDC%) emphasizing the potential of gait as a tool for reliable clinical assessment on the ward. Hence, our results provide a benchmark when putting gait parameters into perspective and designating a change as clinically relevant.…”

“…Consequently, we encourage the evaluation of parameters that are extracted from other IMU positions such as the feet or even comparing multiple analysis algorithms, to understand how the algorithm choice influences reliability. Day-to-day variabilities in sit-to-stand motions [ 15 ], balance aspects [ 9 ] and ambulation [ 30 ] have been described to occur in patients with neurological/neurodegenerative diseases (especially in PD [ 31 ]). It may thus be that gait changes between two consecutive days due to clinical reasons.…”

“…IMUs usually contain accelerometers, gyroscopes and magnetometers, and the subsequent extraction of spatiotemporal gait parameters [ 4 , 5 ] is often based on sensor fusion algorithms [ 6 , 7 ]. While the validity of marker-based motion capture is rarely questioned [ 8 ], the reliability and validity of IMU-based motion capture is under constant evaluation [ 9 ] and the reliability of IMU-based gait parameters is rarely reported.…”

Postural Sway in Parkinson's Disease and Multiple Sclerosis Patients During Tasks With Different Complexity

“…Since we are basically presenting an intra-individual comparison of static balance across different difficulty levels, we do not assume that the preceding information is relevant to this study. Moreover, number of patients were relatively small and the day-to-day variability in the static sway parameters can be relatively high in neurological patients ( 6 ), therefore the results need to be interpreted with caution especially concerning sensitivity. Vice versa, it is very likely that the detected significances actually represent true differences.…”

“…A wearable sensor, worn on the lower back, can provide indirect information on even small movements of the COM. Inertial measurement units (IMUs) have shown to be a valid and reliable tool to quantify static postural sway ( 4 , 5 ), although the extractable variables show markedly different reliabilities ( 6 ). Sway parameters that can be extracted with IMUs are e.g., area, velocity, acceleration and jerk (quick compensatory movements) ( 7 ).…”