Elsevier

Gait & Posture

Volume 51, January 2017, Pages 239-246
Gait & Posture

25 years of lower limb joint kinematics by using inertial and magnetic sensors: A review of methodological approaches

https://doi.org/10.1016/j.gaitpost.2016.11.008Get rights and content

Highlights

  • A 25-years report of methodological contributions for the estimate of lower limb joint kinematics by using inertial sensors is presented.

  • Basic prerequisites for a reliable estimate of joint kinematics are discussed.

  • Contributions are classified according to the computational approach and the relevant instrumental technique.

  • These methodological approaches are discussed from the point of view of their usability in a practical clinical context.

Abstract

Joint kinematics is typically limited to the laboratory environment, and the restricted volume of capture may vitiate the execution of the motor tasks under analysis. Conversely, clinicians often require the analysis of motor acts in non-standard environments and for long periods of time, such as in ambulatory settings or during daily life activities. The miniaturisation of motion sensors and electronic components, generally associated with wireless communications technology, has opened up a new perspective: movement analysis can be carried out outside the laboratory and at a relatively lower cost. Wearable inertial measurement units (embedding 3D accelerometers and gyroscopes), eventually associated with magnetometers, allow one to estimate segment orientation and joint angular kinematics by exploiting the laws governing the motion of a rotating rigid body. The first study which formalised the problem of the estimate of joint kinematics using inertial sensors dates back to 1990. Since then, a variety of methods have been presented over the past 25 years for the estimate of 2D and 3D joint kinematics by using inertial and magnetic sensors. The aim of the present review is to describe these approaches from a purely methodological point of view to provide the reader with a comprehensive understanding of all the instrumental, computational and methodological issues related to the estimate of joint kinematics when using such sensor technology.

Section snippets

Lower limb joint angular kinematics in gait analysis: aims, current practice and new trends

Cappozzo and colleagues stated that “Human movement analysis aims at gathering quantitative information about the mechanics of the musculo-skeletal system during the execution of a motor task” [1]. When the latter refers to human gait, a variety of kinematic variables and related parameters can be used for characterising this motor task [2]. One of these variables is represented by joint angular kinematics (simply “joint kinematics” from now on), which is considered a key descriptor for

Inertial sensors for estimating a body segment’s orientation: a brief “historical” perspective

A common way to introduce inertial sensors in research papers proposing novel methodologies for human movement analysis (including the present paper) is to present inertial sensors as a recent alternative to standard laboratory-based motion analysis technologies. Inertial sensors started to make their appearance, instead, in parallel to camera-based approaches [19]: the first studies on the estimate of segmental orientation indeed date back to 1973 when Morris used six uniaxial accelerometers

On the estimate of the sensor’s orientation

Since joint kinematics has been defined as the relative orientation of two adjacent body segments, its estimate first requires the knowledge of the orientation of each body segment by using inertial sensors. In a bi-dimensional (2D) (i.e., planar) case, joint kinematics is, then, usually computed as the difference between the planar orientation of the adjacent body segments. In the 3D case, just as in stereophotogrammetry, the 3D orientation of the two adjacent body segments is needed. Both in

Segment-to-sensor alignment

When estimating joint kinematics by using inertial sensors, a sensor-to-segment axis alignment is a crucial factor to take into account. As previously said, obtaining the orientation of the body segment from the known orientation of a sensor fixed on the segment is not straightforward. Sensor-to-segment axes alignment is needed for the sake of the functional readability of the measured or derived information content: to be called “joint kinematics”, it has to be the relative orientation between

Estimating joint kinematics by using inertial sensors

The first study which formalised the problem of the estimate of joint kinematics by using inertial sensors dates back to 1990 [28]. Since then, a variety of methodological approaches have been presented over the past 25 years to estimate 2D and 3D joint kinematics by using wearable inertial sensors. Several levels of classification are used in the present paper for classifying the relevant research from 1990 to the present day (Fig. 1). A first level consists in distinguishing between the 2D

Discussion and conclusions

A 25 year methodological review of studies related to the estimation of joint kinematics by means of inertial sensors has been performed. A list of the methodological contributions, along with their relevant main peculiarities and distinctiveness, can be found in Table 1.

Generally, all of the analysed approaches were found to be accurate with respect to standard motion analysis techniques. For this reason, the following debate is going to be addressed more on the practical and “ecological”

Conflicts of interest

The author declare no conflict of interest.

Acknowledgments

No funding were received for the preparation of this paper.

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