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.

Correction to: Trunk, head and pelvis interactions in healthy children when performing seated daily arm tasks.

The authors inadvertently submitted a wrong figure part for publication. Figure 8b should be as follows.

Trunk, head and pelvis interactions in healthy children when performing seated daily arm tasks.

Development of trunk and head supportive devices for children with neuromuscular disorders requires detailed information about pelvis, trunk and head movement in interaction with upper extremity movement, as these are crucial for daily activities when seated in a wheelchair. Twenty-five healthy subjects (6-20 years old) were included to obtain insight in the physiological interactions between these segments and to assess maturation effects. Subjects performed a maximum range of trunk and head movement tasks and several daily tasks, including forward and lateral reaching. Movements of the arms, head, pelvis, and sub-sections of the trunk were recorded with an optical motion capture system. The range of motion of each segment was calculated. Contributions of individual trunk segments to the range of trunk motion varied with movement direction and therefore with the task performed. Movement of pelvis and all trunk segments in the sagittal plane increased significantly with reaching height, distance and object weight when reaching forward and lateral. Trunk movement in reaching decreased with age. Head movement was opposite to trunk movement in the sagittal (> 50% of the subjects) and transverse planes (> 75% of the subjects) and was variable in the frontal plane in most tasks. Both trunk and head movement onsets were earlier compared to arm movement onset. These results provide insight in the role of the upper body in arm tasks in young subjects and can be used for the design of trunk and head supportive devices for children with neuromuscular disorders.

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.

Is the Assessment of 5 Meters of Gait with a Single Body-Fixed-Sensor Enough to Recognize Idiopathic Parkinson's Disease-Associated Gait?

Quantitative assessment of gait in patients with Parkinson's disease (PD) is an important step in addressing motor symptoms and improving clinical management. Based on the assessment of only 5 meters of gait with a single body-fixed-sensor placed on the lower back, this study presents a method for the identification of step-by-step kinematic parameters in 14 healthy controls and in 28 patients at early-to-moderate stages of idiopathic PD. Differences between groups in step-by-step kinematic parameters were evaluated to understand gait impairments in the PD group. Moreover, a discriminant model between groups was built from a subset of significant and independent parameters and based on a 10-fold cross-validated model. The discriminant model correctly classified a total of 89.5% participants with four kinematic parameters. The sensitivity of the model was 95.8% and the specificity 78.6%. The results indicate that the proposed method permitted to reasonably recognize idiopathic PD-associated gait from 5-m walking assessments. This motivates further investigation on the clinical utility of short episodes of gait assessment with body-fixed-sensors.

Estimating 3D L5/S1 moments and ground reaction forces during trunk bending using a full-body ambulatory inertial motion capture system.

Inertial motion capture (IMC) systems have become increasingly popular for ambulatory movement analysis. However, few studies have attempted to use these measurement techniques to estimate kinetic variables, such as joint moments and ground reaction forces (GRFs). Therefore, we investigated the performance of a full-body ambulatory IMC system in estimating 3D L5/S1 moments and GRFs during symmetric, asymmetric and fast trunk bending, performed by nine male participants. Using an ambulatory IMC system (Xsens/MVN), L5/S1 moments were estimated based on the upper-body segment kinematics using a top-down inverse dynamics analysis, and GRFs were estimated based on full-body segment accelerations. As a reference, a laboratory measurement system was utilized: GRFs were measured with Kistler force plates (FPs), and L5/S1 moments were calculated using a bottom-up inverse dynamics model based on FP data and lower-body kinematics measured with an optical motion capture system (OMC). Correspondence between the OMC+FP and IMC systems was quantified by calculating root-mean-square errors (RMSerrors) of moment/force time series and the interclass correlation (ICC) of the absolute peak moments/forces. Averaged over subjects, L5/S1 moment RMSerrors remained below 10Nm (about 5% of the peak extension moment) and 3D GRF RMSerrors remained below 20N (about 2% of the peak vertical force). ICCs were high for the peak L5/S1 extension moment (0.971) and vertical GRF (0.998). Due to lower amplitudes, smaller ICCs were found for the peak asymmetric L5/S1 moments (0.690-0.781) and horizontal GRFs (0.559-0.948). In conclusion, close correspondence was found between the ambulatory IMC-based and laboratory-based estimates of back load.

Working height, block mass and one- vs. two-handed block handling: the contribution to low back and shoulder loading during masonry work.

The goal of this study was to compare the effects of the task variables block mass, working height and one- vs. two-handed block handling on low back and shoulder loading during masonry work. In a mock-up of a masonry work site, nine masonry workers performed one- and two-handed block-lifting and block-placing tasks at varying heights (ranging from floor to shoulder level) with blocks of varying mass (ranging from 6 to 16 kg). Kinematics and ground reaction forces were measured and used in a 3-D linked segment model to calculate low back and shoulder loading. Increasing lifting height appeared to be the most effective way to reduce low back loading. However, working at shoulder level resulted in relatively high shoulder loading. Therefore, it was recommended to organise masonry work in such a way that blocks are handled with the hands at about iliac crest height as much as possible.

Effect of block weight on work demands and physical workload during masonry work.

The effect of block weight on work demands and physical workload was determined for masons who laid sandstone building blocks over the course of a full work day. Three groups of five sandstone block masons participated. Each group worked with a different block weight: 11 kg, 14 kg or 16 kg. Productivity and durations of tasks and activities were assessed through real time observations at the work site. Energetic workload was also assessed through monitoring the heart rate and oxygen consumption at the work site. Spinal load of the low back was estimated by calculating the cumulated elastic energy stored in the lumbar spine using durations of activities and previous data on corresponding compression forces. Block weight had no effect on productivity, duration or frequency of tasks and activities, energetic workload or cumulative spinal load. Working with any of the block weights exceeded exposure guidelines for work demands and physical workload. This implies that, regardless of block weight in the range of 11 to 16 kg, mechanical lifting equipment or devices to adjust work height should be implemented to substantially lower the risk of low back injuries.

The effects of ergonomic interventions on low back moments are attenuated by changes in lifting behaviour.

This study investigated the effects of ergonomic interventions involving a reduction of the mass (from 16 to 11 and 6 kg) and an increase in the initial lifting height (from pallet height to 90 cm above the ground) of building blocks in a mock-up of an industrial depalletizing task, investigating lifting behaviour as well as low back moments (calculated using a 3-D linked segment model). Nine experienced construction workers participated in the experiment, in which they removed building blocks from a pallet in the way they normally did during their work. Most of the changes in lifting behaviour that were found would attenuate the effect of the investigated interventions on low back moments. When block mass was reduced from 16 to 6 kg, subjects chose to lift the building block from a 10 (SD 10) cm greater distance from the front edge of the pallet and with a 100 (SD 66) degrees/s(2) higher trunk angular acceleration. When initial lifting height was increased, subjects chose to shift the building blocks less before actually lifting them, resulting in a 10.7 (SD 10) cm increase in horizontal distance of the building blocks relative to the body at the instant of peak net total moment. Despite these changes in lifting behaviour, the investigated ergonomic interventions still reduced the net total low back moment (by 4.9 (SD 2.0) Nm/kg when block mass was reduced and 53.6 (SD 41.0) Nm when initial lifting height was increased).