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Joint kinematics estimate using wearable inertial and magnetic sensing modules

BACKGROUND AND AIMS In many applications, it is essential that the evaluation of a given motor task is not affected by the restrictions of the laboratory environment. To accomplish this requirement, miniature triaxial inertial and magnetic sensors can be used. This paper describes an anatomical calibration technique for wearable inertial and magnetic sensing modules based on the direct measure of the direction of anatomical axes using palpable anatomical landmarks. An anatomical frame definition for the estimate of joint angular kinematics of the lower limb is also proposed. METHODS The performance of the methodology was evaluated in an upright posture and a walking trial of a single able-bodied subject. The repeatability was assessed with six examiners performing the anatomical calibration, while its consistency was evaluated by comparing the results with those obtained using stereophotogrammetry. RESULTS Results relative to the up-right posture trial revealed an intra- and inter-examiner variability which is minimal in correspondence to the flex-extension angles (0.2-2.9 degrees ) and maximal to the internal-external rotation (1.6-7.3 degrees ). For the level walking, the root mean squared error between the kinematics estimated with the two measurement techniques varied from 2.5% to 4.8% of the range of motion for the flex-extension, whereas it ranged from 13.1% to 41.8% in correspondence of the internal-external rotation. CONCLUSION The proposed methodology allowed for the estimate of lower limb joint angular kinematics in a repeatable and consistent manner, enabling inertial and magnetic sensing based systems to be used especially for outdoor human movement analysis applications.

An optimized Kalman filter for the estimate of trunk orientation from inertial sensors data during treadmill walking

The aim of this study was the fine tuning of a Kalman filter with the intent to provide optimal estimates of lower trunk orientation in the frontal and sagittal planes during treadmill walking at different speeds using measured linear acceleration and angular velocity components represented in a local system of reference. Data were simultaneously collected using both an inertial measurement unit (IMU) and a stereophotogrammetric system from three healthy subjects walking on a treadmill at natural, slow and fast speeds. These data were used to estimate the parameters of the Kalman filter that minimized the difference between the trunk orientations provided by the filter and those obtained through stereophotogrammetry. The optimized parameters were then used to process the data collected from a further 15 healthy subjects of both genders and different anthropometry performing the same walking tasks with the aim of determining the robustness of the filter set up. The filter proved to be very robust. The root mean square values of the differences between the angles estimated through the IMU and through stereophotogrammetry were lower than 1.0° and the correlation coefficients between the corresponding curves were greater than 0.91. The proposed filter design can be used to reliably estimate trunk lateral and frontal bending during walking from inertial sensor data. Further studies are needed to determine the filter parameters that are most suitable for other motor tasks.

Wearable inertial sensors for human movement analysis

ABSTRACT Introduction: The present review aims to provide an overview of the most common uses of wearable inertial sensors in the field of clinical human movement analysis. Areas covered: Six main areas of application are analysed: gait analysis, stabilometry, instrumented clinical tests, upper body mobility assessment, daily-life activity monitoring and tremor assessment. Each area is analyzed both from a methodological and applicative point of view. The focus on the methodological approaches is meant to provide an idea of the computational complexity behind a variable/parameter/index of interest so that the reader is aware of the reliability of the approach. The focus on the application is meant to provide a practical guide for advising clinicians on how inertial sensors can help them in their clinical practice. Expert commentary: Less expensive and more easy to use than other systems used in human movement analysis, wearable sensors have evolved to the point that they can be considered ready for being part of routine clinical routine.

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

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.

Acute kinematic adaptations to running on a centrifugal track: A pilot study

The centrifugal track, a basin-shaped track characterised by a platform with a parabolic section, exploits the centripetal acceleration to increase the bodyweight of the athlete during the foot contact phase of running. Because this overload is produced by an inertial force that is equally distributed to the infinitesimal point masses of the body, no postural changes are expected with respect to level running. This pilot study aimed to compare some selected key kinematic quantities of running on the centrifugal track with respect to level running. A video-based three-dimensional (3D) motion analysis was performed on five sprinters and used to compute spatio-temporal variables, frontal and sagittal trunk kinematics and knee sagittal kinematics at footstrike, midstance and foot-off over two consecutive steps at similar speeds. No significant changes were found in spatio-temporal variables and knee kinematics between the right and the left leg during running on the centrifugal track. Neither step length nor step duration was found statistically different between the two running typologies. Trunk flexion was not altered during the stance phase of running on the centrifugal track. Knee angle at footstrike was found similar to level running. A slightly larger but statistically significant knee flexion at midstance and knee extension at foot-off were found with respect to flat-track running, but these findings appear more beneficial for strength training rather than detrimental for the running technique. The centrifugal track was found to be a viable alternative to the common resisted sprint training techniques as the training effect is produced without localised overloads on the musculoskeletal system and detrimental postural changes.