Ambulatory Measurement System Research Articles

Validation of a wearable system for 3D ambulatory L5/S1 moment assessment during manual lifting using instrumented shoes and an inertial sensor suit

This study aimed to evaluate the accuracy of 3D L5/S1 moment estimates from an ambulatory measurement system consisting of a wearable inertial motion capture system (IMC) and instrumented force shoes (FSs), during manual lifting. Reference L5/S1 moments were calculated using an inverse dynamics bottom-up laboratory model (buLABmodel), based on data from a measurement system comprising optical motion capture (OMC) and force plates (FPs). System performance of (1) a bottom-up ambulatory model (buAMBmodel) using lower-body kinematic IMC and FS data, and (2) a top-down ambulatory model (tdAMBmodel) using upper-body kinematic IMC data and hand forces (HFs) were compared. HFs were estimated using full-body kinematic IMC data and FS forces.Eight males and eight females lifted a 10-kg box from different initial vertical/horizontal positions using either a free or an asymmetric lifting style. As a measure of system performance, root-mean-square (RMS) errors were calculated between the reference (buLABmodel) and ambulatory (tdAMBmodel &buAMBmodel) moments.The results showed two times smaller errors for the tdAMBmodel (averaged RMS errors < 20 Nm or 10% of peak extension moment) than for the buAMBmodel (average RMS errors < 40 Nm or 20% of peak extension moment). In conclusion, for ambulatory L5/S1 moment assessment with an IMC + FS system, using a top-down inverse dynamics approach with estimated hand forces is to be preferred over a bottom-up approach.

Continuous ambulatory hand force monitoring during manual materials handling using instrumented force shoes and an inertial motion capture suit

Hand forces (HFs) are commonly measured during biomechanical assessment of manual materials handling; however, it is often a challenge to directly measure HFs in field studies. Therefore, in a previous study we proposed a HF estimation method based on ground reaction forces (GRFs) and body segment accelerations and tested it with laboratory equipment: GFRs were measured with force plates (FPs) and segment accelerations were measured using optical motion capture (OMC). In the current study, we evaluated the HF estimation method based on an ambulatory measurement system, consisting of inertial motion capture (IMC) and instrumented force shoes (FSs).Sixteen participants lifted and carried a 10-kg crate from ground level while 3D full-body kinematics were measured using OMC and IMC, and 3D GRFs were measured using FPs and FSs. We estimated 3D hand force vectors based on: (1) FP+OMC, (2) FP+IMC and (3) FS+IMC. We calculated the root-mean-square differences (RMSDs) between the estimated HFs to reference HFs calculated based on crate kinematics and the GRFs of a FP that the crate was lifted from.Averaged over subjects and across 3D force directions, the HF RMSD ranged between 10-15N when using the laboratory equipment (FP + OMC), 11-18N when using the IMC instead of OMC data (FP+IMC), and 17-21N when using the FSs in combination with IMC (FS + IMC). This error is regarded acceptable for the assessment of spinal loading during manual lifting, as it would results in less than 5% error in peak moment estimates.

Modular finger and hand motion capturing system based on inertial and magnetic sensors

Abstract: The assessment of hand posture and kinematics is increasingly important in various fields. This includes the rehabilitation of stroke survivors with restricted hand function. This paper presents a modular, ambulatory measurement system for the assement of the remaining hand function and for closed-loop controlled therapy. The device is based on inertial sensors and utilizes up to five interchangeable sensor strips to achieve modularity and to simplify the sensor attachment. We introduce the modular hardware design and describe algorithms used to calculate the joint angles. Measurements with two experimental setups demonstrate the feasibility and the potential of such a tracking device.

Push Characteristics in Wheelchair Court Sport Sprinting

Short sprints are important components of most wheelchair court sports, since being faster than the opponent often determines keeping ball possession or not. Sprinting capacity is best measured during a field test, allowing the athlete to freely choose push strategies adapted to their own wheelchair setting, physical ability, classification and speed changes during a sprint. The key test outcome is sprint duration, but there are various ways to accomplish the same sprint time. So can different push strategies be identified in a wheelchair sport and how do they relate to athlete level/classification and wheelchair configuration? These relationships were investigated by field tests of 30 male wheelchair basketball athletes during a 12 meter sprint in their own wheelchair. A recently developed method for ambulatory measurement was used to calculate wheelchair kinematics [1], providing outcomes on displacement, speed, acceleration and pushes. Additionally maximal isometric push force was recorded and rear seat height was noted. Within the measured athletes, internationals were expected to be faster due to a better physical training status and technique, allowing them to sprint with fewer (but more powerful) pushes. Likewise, athletes of higher classification were expected to be faster due their superior physical capacity, but the effect on the number of pushes used was not that evident. Video analysis was added to validate push detection of the ambulatory measurement system. Mutual correlations and competition level differences of sprint characteristics were calculated. General Linear Models (GLM) were drawn to determine the effect of competition level and classification on sprint time and number of pushes.In the overall dataset sprint characteristics did not correlate significantly with classification, but if split by competition level, there were significant correlations with sprint time (r=-0.715, p=0.006) and number of pushes (r=-0.647, p= 0.017) in the national level athletes. Sprint time, number of pushes and isometric push force differed significantly between national and international level wheelchair basketball athletes. Competition level showed to be a significant (p<0.05) factor in univariate GLMs for sprint time and number of pushes, whereas classification did not. The interaction of competition level and classification as a factor in univariate GLMs was significant.As hypothesized, international level athletes were faster with fewer pushes, even though their higher average seat height was less optimal for propulsion [2]. The interaction effect of competition level and classification in the GLM indicates that the effect of classification on sprint time and number of pushes is different between competition levels. Indeed, in the national level athletes there was a clear relationship between classification and sprint time / number of pushes, but not in internationals. This difference is pointing at a more professional level of wheelchair configuration or better technique of the international athletes regarding sprint performance. Given the correlation between seat height and classification, the seat height of lowly classified athletes seemed optimized for sprinting, whereas seat height of highly classified athletes with already adequate sprinting capacity was optimized for upward reach. Future research based on larger groups with more even distribution over classifications could provide more solid models and reveal more detailed insight in push strategy efficacy. Given the proven reliability of the inertial sensor based method [1] and the proven reliability for push detection in sprinting, this research could well be performed using this easy to use ambulatory method. Although more challenging than well controlled experimental research, the field based setting in this research revealed additional information not only describing the relation between wheelchair setting and performance, but also describing its practical applications if other game demands were taken into account. The results of this approach is believed to assist athletes, coaches and wheelchair experts in decision making concerning wheelchair configuration and athlete training.

Noninvasive ambulatory measurement system of cardiac activity.

This work implements a noninvasive system that measures the movements caused by cardiac activity. It uses unobtrusive Electro-Mechanical Films (EMFi) on the seat and on the backrest of a regular chair. The system detects ballistocardiogram (BCG) and respiration movements. Real data was obtained from 54 volunteers. 19 of them were measured in the laboratory and 35 in a hospital waiting room. Using a BIOPAC acquisition system, the ECG was measured simultaneously to the BCG for comparison. Wavelet Transform (WT) is a better option than Empirical Mode Decomposition (EMD) for signal extraction and produces higher effective measurement time. In the laboratory, the best results are obtained on the seat. The correlation index was 0.9800 and the Bland-Altman limits of agreement were 0.7136 ± 4.3673 [BPM]. In the hospital waiting room, the best results are also from the seat sensor. The correlation index was 0.9840, and the limits of agreement were 0.4386 ± 3.5884 [BPM]. The system is able to measure BCG in an unobtrusive way and determine the cardiac frequency with high precision. It is simple to use, which means the system can easily be used in non-standard settings: resting in a chair or couch, at the gym, schools or in a hospital waiting room, as shown.

Pre-operative ambulatory measurement of asymmetric lower limb loading during walking in total hip arthroplasty patients

BackgroundTotal hip arthroplasty is a successful surgical procedure to treat hip osteoarthritis. Clinicians use different questionnaires to assess the patient’s pain and functional capacity. Furthermore, they assess the quality of gait in a very global way.This clinical evaluation usually shows significant improvement after total hip arthroplasty, however, does not provide objective, quantifiable information about the movement patterns underlying the functional capacity, which can currently only be obtained in a gait laboratory. Instrumented force shoes can quantify gait velocity, ground reaction forces and the gait pattern easily in an outpatient setting.The main goal of this study was to investigate how mobility characteristics during walking, relate to gait velocity and questionnaire outcomes of patients with hip osteoarthritis in an outpatient setting.Methods22 patients with primary osteoarthritis of the hip selected for a total hip arthroplasty participated in this study. For each patient the Harris Hip Score, the Traditional Western Ontario and the McMaster Universities osteoarthritis index were administered. Subsequently, the patients were instructed to walk through the corridor while wearing instrumented shoes. The gait velocity estimated with the instrumented force shoes was validated measuring the time required to walk a distance of 10 m using a stopwatch and a measuring tape as a reference system. A regression analysis between spatial, temporal, ground reaction force parameters, including asymmetry, and the gait velocity and the questionnaires outcomes was performed.ResultsThe velocity estimated with the instrumented shoes did not differ significantly from the velocity measured independently. Although gait parameters correlated significantly with velocity, symmetry index parameters were not correlated with velocity. These symmetry index parameters show significant inter-limb asymmetry during walking. No correlation was found between any of the variables studied and questionnaires outcomes.ConclusionInter-limb asymmetry can be evaluated with the instrumented shoes supplying important additional information about the individual gait pattern, which is not represented by gait velocity and questionnaires usually used. Therefore, this new ambulatory measurement system is able to provide complementary information to gait velocity and questionnaires outcomes to assess the functional capacity of patients with hip osteoarthritis.

Characterization of gait pattern by 3D angular accelerations in hemiparetic and healthy gait

Characterization of gait pattern is of interest for clinical gait assessment. Past developments of ambulatory measurement systems have still limitations for daily usage in the clinical environment. This study investigated the potential of 3D angular accelerations of foot, shank, and thigh to characterize gait events and phases of ten healthy and ten hemiparetic subjects. The key feature of the system was the use of angular accelerations obtained by differential measurement. Further, the effect of sensor position and walking cadence on the signal was investigated. We found that gait phases are characterized as modulated amplitudes of angular accelerations of foot, shank, and thigh. Increasing the gait cadence from 70steps/min to 100steps/min caused an amplitude increase of the magnitude of the vector, summing all 3D angular accelerations on the sensor position (p<0.001). Comparison of healthy and hemiparetic gait showed a lower mean of the magnitude of the vector during the loading response in the hemiparetic gait (p<0.05), while during pre-swing and swing no significant differences between healthy and hemiparetic gait were observed. A comparison of the tangential acceleration component in the frontal plane showed no statistically significant difference between healthy and hemiparetic gait. Further, no statistically significant difference between the tangential components was found for both groups. This method demonstrated promising results for a possible use for gait assessment.

Ambulatory estimation of foot placement during walking using inertial sensors

This study proposes a method to assess foot placement during walking using an ambulatory measurement system consisting of orthopaedic sandals equipped with force/moment sensors and inertial sensors (accelerometers and gyroscopes). Two parameters, lateral foot placement (LFP) and stride length (SL), were estimated for each foot separately during walking with eyes open (EO), and with eyes closed (EC) to analyze if the ambulatory system was able to discriminate between different walking conditions. For validation, the ambulatory measurement system was compared to a reference optical position measurement system (Optotrak). LFP and SL were obtained by integration of inertial sensor signals. To reduce the drift caused by integration, LFP and SL were defined with respect to an average walking path using a predefined number of strides. By varying this number of strides, it was shown that LFP and SL could be best estimated using three consecutive strides. LFP and SL estimated from the instrumented shoe signals and with the reference system showed good correspondence as indicated by the RMS difference between both measurement systems being 6.5±1.0 mm (mean ±standard deviation) for LFP, and 34.1±2.7 mm for SL. Additionally, a statistical analysis revealed that the ambulatory system was able to discriminate between the EO and EC condition, like the reference system. It is concluded that the ambulatory measurement system was able to reliably estimate foot placement during walking.

Ambulatory Estimation of Center of Mass Displacement During Walking

The center of mass (CoM) and the center of pressure (CoP) are two variables that are crucial in assessing energy expenditure and stability of human walking. The purpose of this study is to estimate the CoM displacement continuously using an ambulatory measurement system. The measurement system consists of instrumented shoes with 6 DOF force/moment sensors beneath the heels and the forefeet. Moreover, two inertial sensors are rigidly attached to the force/moment sensors for the estimation of position and orientation. The estimation of CoM displacement is achieved by fusing low-pass filtered CoP data with high-pass filtered double integrated CoM acceleration, both estimated using the instrumented shoes. Optimal cutoff frequencies for the low-pass and high-pass filters appeared to be 0.2 Hz for the horizontal direction and 0.5 Hz for the vertical direction. The CoM estimation using this ambulatory measurement system was compared to CoM estimation using an optical reference system based on the segmental kinematics method. The rms difference of each component of the CoM displacement averaged over a hundred trials obtained from seven stroke patients was ( 0.020 +/-0.007 ) m (mean +/- standard deviation) for the forward x-direction, ( 0.013 +/-0.005) m for the lateral y-direction, and ( 0.007 +/-0.001) m for the upward z-direction. Based on the results presented in this study, it is concluded that the instrumented shoe concept allows accurate and continuous estimation of CoM displacement under ambulatory conditions.

Polymeric barrier membranes for device packaging, diffusive control and biocompatibility

Current state-of-the-art implantable micron feature electronic devices are capable of monitoring and stimulating functions in vivo. Within an EU Framework VI project a further step was taken in developing key microsystem technologies and communication methods that could bring intelligence directly to the human interface, in the form of reactive medical implants and ambulatory measurement systems. Information from these devices is planned to be transmitted out into the wider environment for remote processing. However, the packaging of such state-of-the-art devices to enhance tissue biocompatibility, and to protect conducting elements from in vivo corrosion during extended use, along with protecting the body from toxins leaching from implant components, remains a concern. Candidate polymeric barriers as hydration resistant and solute impermeable interfaces to mitigate such major problems of chronic implantation were investigated. Materials studied included silicone rubber, PVC, polyurethane, and diamond-like carbon (DLC). Polymer permeability to water solutes was marginally improved through incorporation of lipid into these structures. Surface biocompatibility was assessed on the basis of protein film deposition in vitro and by cell viability studies in tissue culture. Short-term toxicity was not observed for any of the tested materials, though there were substantial differences in hydration. Additionally, polypyrrole over active electrodes shows feasibility for controlled tissue interfacing whilst retaining electrical conductivity.

AMBULATORY MEASUREMENT OF GROUND REACTION FORCE AND ESTIMATION OF ANKLE AND FOOT DYNAMICS

INTRODUCTION Traditionally, human body movement analysis is done in so-called ‘gait laboratories’. In these laboratories, body movement is measured by a camera system using optical markers, the ground reaction force by a force plate fixed in the floor, and the muscle activity by EMG. From the body movements and ground reaction forces, joint moments and powers can be estimated by applying inverse dynamics methods. However, the main drawback is the restriction to the laboratory environment. In order to overcome this lab restriction, several research groups try to develop ambulatory measurement systems (e.g. [2]). This study presents an ambulatory measurement system for the measurement of the Ground Reaction Force (GRF), and the estimation of ankle and foot dynamics. METHODS The measurement system consisted of an orthopaedic sandal with two six degrees-of-freedom force/moment sensors beneath the heel and the forefoot (Figure 1). The position and orientation of heel and forefoot were estimated using the 3D accelerometer and 3D gyroscope of two miniature inertial ensors (Xsens Motion Technologies, http://www.xsens), rigidly attached to the force sensors. Moreover, a third inertial sensor was attached to the lower leg. The GRF was measured by the force/moment sensors beneath the shoe. A derivation of the calculation of the dynamics of ankle and foot can be found in [1]. The performance of the developed measurement system was evaluated by comparing the ambulatory measurement system with a reference measurement system, consisting of an optical measurement system (Vicon) and a force plate (AMTI). During the measurements, a healthy subject wearing the instrumented shoes, inertial sensors and optical markers, was asked to walk repeatedly over the force plate. In order to compare the signals measured with both measurement systems, a global coordinate system was defined with the x-axis pointing forward, the y-axis to the right, and the z-axis upward, resulting in a right-handed orthogonal coorinate system. RESULTS AND DISCUSSION The three components of the measured GRF of a healthy subject are shown in Figure 2. The signals measured with the instrumented shoe show good correspondence with the signals measured with the force plate, which is confirmed by the root-mean-square error between the magnitudes of the GRF, being 0.02 N/N or 1.8 % of the maximal magnitude. Figure 3 shows an integration of the measured GRF with the estimated position of the heel and forefoot sensor. The figure indicates the possibility of the ambulatory measurement system to measure several steps during a single measurement, which is not possible with the reference system. A detailed discussion about the performance of the ambulatory measurement system can be found in [1]. REFERENCES 1. Schepers HM, et al. IEEE Trans. Biomed. Eng., Accepted, 2007. 2.Baten CTM, et al. ISEK, Torino, Italy, 2006. ACKNOWLEDGEMENTS This research is part of the FreeMotion project, supported by the Dutch Ministry of Economic Affairs.