Full length articleValidation of a commercial inertial sensor system for spatiotemporal gait measurements in children
Introduction
The past several years have seen increased use of inertial sensors to analyze movement in laboratory, clinic, and daily living environments [1]. By utilizing accelerometers, gyroscopes, or magnetometers (or a combination of these), inertial sensors can provide a wealth of data regarding the characteristics of global and segment-specific movement during a variety of tasks. Additionally, the sensors and recording equipment are relatively compact, portable, and low cost compared to traditional laboratory-based equipment (such as multi-camera 3D motion capture or instrumented mats), and can be used to collect human movement data in environments and contexts where the use of traditional equipment is not possible. Inertial sensor technology that can be used in both laboratory and clinical environments has the potential to be a widely applicable method for researchers and clinicians to evaluate gait in a variety of healthy and clinical populations.
One widely-used inertial sensor system is the MobilityLab system (APDM, Portland, OR). This system utilizes six inertial sensors, each containing tri-axial accelerometers, gyroscopes, and magnetometers providing a comprehensive evaluation of the spatiotemporal characteristics of motion during a variety of pre-programmed testing protocols [2], [3], [4]. Data collected from these sensors is transmitted wirelessly to a software program, which uses algorithms based on aggregated reference data that have been validated against both 3D motion capture and force plate data to calculate the spatiotemporal characteristics (such as stride time, stride length, and velocity of each stride) of movement [3], [4], [5]. The system is also capable of discriminating between different movements associated with various mobility tests such as the sit-to-stand and turning phases of the timed-up-and-go test [6], and has been used in the evaluation of gait and mobility in clinical populations including persons with Parkinson’s disease and multiple sclerosis [7], [8].
While previous research has indicated that inertial sensor systems such as MobilityLab are a valid and reliable method of analyzing movement in adults [9], there has yet to be any research on the validity of their use in children. Since achieving functional gait and maximizing ambulatory independence are two of the most important functional outcomes for children suffering from musculoskeletal and neurological pathologies [10], it is crucial for clinicians to be able to analyze gait in children to recognize and attempt to correct any impairments and sub-optimal movement patterns that may be limiting functional capacity. Compared to traditional measurement tools used for gait analysis, inertial sensors offer several distinct benefits when working with children. The sensors are much easier to don and doff than reflective marker sets and use Velcro straps rather than adhesives, reducing the chances of skin irritation and/or discomfort during removal. Additionally, while most methods of gait analysis restrict movement to a given space or require the child to contact a target with their foot, the sensors allow the child to walk using their normal movement pattern with no environmental constraints.
While some research exists evaluating the use of inertial sensors as a tool for gait analysis in children with cerebral palsy [11], [12], [13], there are currently no data evaluating the validity of inertial sensor systems relative to 3D motion capture (the gold standard of gait analysis). Direct measurements of kinematic parameters like linear acceleration and angular velocity from inertial systems are fairly accurate; however indirect measures such as spatiotemporal parameters often rely on algorithms with assumptions and reference values based on adult data. It is unclear if these approaches will result in accurate data when applied to children.
The objective of this study is to validate the use of the MobilityLab inertial sensor system to obtain spatiotemporal parameters of gait in typically-developing children by comparing the level of agreement between data from the sensors and those obtained via 3D motion capture. We hypothesize that temporal data based on event detection will be accurate but estimations of spatial data may be influenced by adult-data assumptions inherent to the MobilityLab algorithms.
Section snippets
Methods
Ten typically-developing children (five males) participated in the study (mean age 5.1 yrs, range 3.0 yrs–8.3 yrs). Participants were eligible for the study if they were between the ages of three and 10, free of any neurological disorders or lower limb musculoskeletal injuries, and were full term (≥37 weeks gestational age) at birth. The study was approved by the institutional Research Ethics Board and informed consent was obtained from the children’s guardians. In addition to obtaining
Results
StnT and StrT were comparable between systems with little bias (Fig. 1). The LoA for StnT and StrT were approximately +/−0.05 s and +/−0.02 s respectively (Fig. 1). Even though the bias and LoA for the StrT were not constant, they were approximately equal to two motion capture sample point intervals. Examination of the raw foot fall data showed that 93% of initial contact and 68% of toe off identifications from the inertial system were within one frame of the motion capture system.
StrL showed a
Discussion
This study examined the accuracy of MobilityLab, a commercial inertial sensor system, for analyzing basic spatiotemporal gait parameters in young children. MobilityLab produced accurate results for temporal gait variables which were comparable to what can be obtained with a 3D motion capture system. For the spatial variable of StrL, the MobilityLab algorithm overestimated short strides and underestimated long strides. A regression analysis was used to generate a StrL correction formula based on
Conclusion
Although previous studies have confirmed the validity of inertial sensors for use during gait analysis in adults, our study represents the first instance where the validity of inertial sensor measurements have been evaluated in children. Although we found the MobilityLab system to be a valid measure for temporal gait parameters and event detection, the system demonstrated a consistent bias with respect to StrL. A regression equation was used to correct for the observed bias, resulting in a
Conflict of interest
The authors have no conflicts of interest.
Acknowledgements
Funding for this study was provided by the Spina Bifida and Hydrocephalus Association of Canada. The sponsor was not directly involved in the design or the study, the collection/analysis/interpretation of data, or the production of this manuscript. The authors would like to thank all of the participants.
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