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.     

Dynamically and statically determined low back moments during lifting

Assessment of the effects of lifting on the low back has most frequently been done with the aid of static models. Many lifting movements appear to have substantial inertial components. It was of interest, therefore, to determine the size of the difference between statically and dynamically calculated lumbar moments during a demanding but not unusual manual lift observed in a metal fabrication industry.

The results of several trials by four young men showed that the dynamic model resulted in peak L4 L5 moments 19% higher on average, with a maximum difference of 52%, than those determined from the static model. The technique adopted in the lift could minimize the difference. When the inertial forces of the load itself and the load weight were incorporated into an otherwise static model (quasi-dynamic) then the resulting L4/L5 moments exceeded those of the fully dynamic model by 25%.

In many industrial tasks static analyses may severely underestimate the demands of dynamic lifts. These results show that a reasonably inexpensive approach in lifting task analysis is to measure the dynamic forces of the load on the hands and to use these in an otherwise static model. This results in a conservative assessment of the injury risk of lifts at least of the type reported in this study.     

Bone position estimation from skin marker co-ordinates using global optimisation with joint constraints

Widespread use of gait or motion analysis in the diagnosis of patients with locomotor pathology and the subsequent planning and assessment of treatment has been limited because of its reliability, particularly in evaluating frontal and transverse plane components. This is because spatial reconstruction of the musculoskeletal system and calculation of its kinematics and kinetics via a skin marker-based multi-link model are subject to marker skin movement artefacts. Traditional methods treat each body segment separately without imposing joint constraints, resulting in apparent dislocations at joints predominantly because of skin movement artefacts. An optimisation method for the determination of the positions and orientations of multi-link musculoskeletal models from marker co-ordinates is presented. It is based on the minimisation of the weighted sum of squared distances between measured and model-determined marker positions. The model imposes joint constraints. Numerical experiments were performed to show that the new method is capable of eliminating joint dislocations and giving more accurate model position and orientation estimations. It is suggested that, with joint constraints and a global error compensation scheme, the effects of measurement errors on the reconstruction of the musculoskeletal system and subsequent mechanical analyses can be reduced globally. The proposed method minimises errors in axial rotation and ab/adduction at the joints and may extend the applicability of gait analysis to clinical problems.     

Biomechanical analysis of manual lifting tasks

This paper presents the findings of a study conducted to determine peak forces generated in the human spine while the individual is engaged in lifting maximum acceptable weight. Calculations of forces and moments, acting on each body segment, were based on film data collected on four individuals for twelve variations of the manual lifting task. The variations were defined by: box-size (three different boxes were used), presence or absence of handles, and symmetry and asymmetry of the lifting task (sagittal and nonsagittal lifting). In general, lower loads were accepted for lift when lifting asymmetrically or when lifting boxes without handles or when lifting bigger boxes. However, peak forces (compressive and shear forces in the spine and ground reaction forces) for these situations were not always lower than those generated when handling either compact boxes or boxes with handles or when lifting boxes symmetrically in the sagittal plane. On the basis of these results, it was concluded that lifting loads asymmetrically or in boxes without handles or in bulky boxes is relatively much more stressful than lifting the same load symmetrically or in boxes with handles or in compact boxes.     

Combining position and acceleration measurements for joint force estimation

The calculation of joint forces in biomechanics is usually based on the measurements of the kinematics of a given body segment, the estimation of the inertial properties of that segment and the solution of the ‘inverse dynamics problem’. Such a process results in estimates of the joint forces and moments needed to sustain the monitored motion. This paper presents a new approach that combines position and acceleration measurements for the purpose of deriving high-quality joint force estimates. An experimental system that is based on an instrumented compound pendulum was designed and tested. The joint forces necessary to maintain a swinging motion of the pendulum were measured by an array of strain gauges, and were compared to the forces estimated by the integrated kinematic segment that measured the position and acceleration of the pendulum. The joint force measurements were also compared to the force estimates that were based on the calculated segmental acceleration generated by the differentiation of the segmental position alone. The results show a high degree of correlation between the forces estimated by the integrated segment and those measured by the strain gauges. The force estimates based on the position measurements alone were less accurate and noisier. The application of the integrated segment to the study of human kinetics is discussed and illustrated by the ankle and knee forces during slow walking. The results suggest that the use of accelerometers is necessary for the estimation of transients and high-frequency components of joint forces.     

A comparison of metatarsophalangeal joint center locations on estimated joint moments during running

The forefoot functions as the base of support during late stance, rotating about the dual-axis of the metatarsophalangeal joints. Previous research has shown that joint axis definition affects estimated joint moments about the forefoot. However, little is known about how metatarsophalangeal joint center definition affects estimated joint kinetics. This study compared moments about the metatarsophalangeal joint using four different defined joint centers. There was a significant difference (p < .001) in peak moments between joint center definitions, differing by up to 0.488 N-m/kg for the slow and 0.878 N-m/kg for the fast running speeds tested. Additionally, there was a significant difference (p < .001) for when peak plantar flexor moment occurred during the slower running condition. The more posteriorly oriented joint centers resulted in higher moments and earlier onset of the plantar flexor moment. In addition to careful modeling of the metatarsophalangeal joint axis, it is recommended that joint center definition should be considered as well.     

A biomechanical model of the lumbosacral joint during lifting activities

A biomechanical model of the lumbosacral region was constructed for the purpose of systematically studying the combined stresses and strains on the local ligaments, muscles and disc tissue during sagittal plane two-handed lifting. The model was validated in two ways. The first validation was a comparison of experimental study results with model predictions. In general predictions compared very reasonably with observed values of several authors with the exception of strain predictions on the articular ligaments. Second, a sensitivity analysis was performed over a wide range of lifting tasks. The predicted stress/strain values followed anticipated patterns and were of reasonable magnitudes. On the basis of the results of the sensitivity analysis it was concluded that typical lifting tasks can lead to excessive disc compressive forces, muscle moment generation requirements, and possibly lumbodorsal fascia strains. Conversely, annulus rupture of a healthy disc due to overstrain appears very unlikely.     

Characterization of the shoulder net joint moment during manual wheelchair propulsion using four functional axes

Understanding how individuals distribute mechanical demand imposed on their upper extremity during physically demanding activities provides meaningful insights to preserve function and mitigate detrimental mechanical loading of the shoulder. In this study, we hypothesized that parameterization of the shoulder net joint moment using four functional axes could characterize distribution tendencies about the shoulder during manual wheelchair propulsion and that regardless of demographics, a shoulder flexor dominant NJM distribution would be predominantly used by individuals with paraplegia (n = 130). Forces and kinematics of the upper extremity and trunk were quantified using motion capture and an instrumented wheel during steady state manual wheelchair propulsion at self-selected fast speeds on a stationary ergometer. The results indicate that parsing out the internal/external rotation component of the shoulder net joint moment about the upper arm and distributing the remainder across the three orthogonal axes of the torso was successful in identifying common shoulder net joint moment distribution techniques used across individuals with paraplegia during manual wheelchair propulsion. Distribution tendencies were predominantly flexor dominant across injury level, gender, time since injury, body mass index, and height demographics. The 4-axis parameterization of the shoulder NJM effectively differentiated moment distribution tendencies used by individuals during manual wheelchair propulsion using a functionally relevant representation of shoulder kinetics. Use of the four-axis parameterization of joint kinetics in future studies is expected to provide important insights that can advance knowledge, preserve function, and inform clinical decisions.     

Lower extremity joint moments during carrying tasks in children

Farm youth often carry loads that are proportionally large and/or heavy, and field measurements have determined that these tasks are equivalent to industrial jobs with high injury risks. The purpose of this study was to determine the effects of age, load amount, and load symmetry on lower extremity joint moments during carrying tasks. Three age groups (8-10 years, 12-14 years, adults), three load amounts (0%, 10%, 20% BW), and three load symmetry levels (unilateral large bucket, unilateral small bucket, bilateral small buckets) were tested. Inverse dynamics was used to determine maximum ankle, knee, and hip joint moments. Ankle dorsiflexion, ankle inversion, ankle eversion, knee adduction, and hip extension moments were significantly higher in 8-10 and 12-14 year olds. Ankle plantar flexion, ankle inversion, knee extension, and hip extension moments were significantly increased at 10% and 20% BW loads. Knee and hip adduction moments were significantly increased at 10% and 20% BW loads when carrying a unilateral large bucket. Of particular concern are increased ankle inversion and eversion moments for children, along with increased knee and hip adduction moments for heavy, asymmetrical carrying tasks. Carrying loads bilaterally instead of unilaterally avoided increases in knee and hip adduction moments with increased load amount.     

Bone orientation and position estimation errors using Cosserat point elements and least squares methods: Application to gait

The aim of this study was to analyze the accuracy of bone pose estimation based on sub-clusters of three skin-markers characterized by triangular Cosserat point elements (TCPEs) and to evaluate the capability of four instantaneous physical parameters, which can be measured non-invasively in vivo, to identify the most accurate TCPEs. Moreover, TCPE pose estimations were compared with the estimations of two least squares minimization methods applied to the cluster of all markers, using rigid body (RBLS) and homogeneous deformation (HDLS) assumptions. Analysis was performed on previously collected in vivo treadmill gait data composed of simultaneous measurements of the gold-standard bone pose by bi-plane fluoroscopy tracking the subjects' knee prosthesis and a stereophotogrammetric system tracking skin-markers affected by soft tissue artifact. Femur orientation and position errors estimated from skin-marker clusters were computed for 18 subjects using clusters of up to 35 markers. Results based on gold-standard data revealed that instantaneous subsets of TCPEs exist which estimate the femur pose with reasonable accuracy (median root mean square error during stance/swing: 1.4/2.8 deg for orientation, 1.5/4.2 mm for position). A non-invasive and instantaneous criteria to select accurate TCPEs for pose estimation (4.8/7.3 deg, 5.8/12.3 mm), was compared with RBLS (4.3/6.6 deg, 6.9/16.6 mm) and HDLS (4.6/7.6 deg, 6.7/12.5 mm). Accounting for homogeneous deformation, using HDLS or selected TCPEs, yielded more accurate position estimations than RBLS method, which, conversely, yielded more accurate orientation estimations. Further investigation is required to devise effective criteria for cluster selection that could represent a significant improvement in bone pose estimation accuracy.     

Comparison of 3D dynamic virtual model to link segment model for estimation of net L4/L5 reaction moments during lifting

The purpose of this study was to validate a 3D dynamic virtual model for lifting tasks against a validated link segment model (LSM). A face validation study was conducted by collecting x, y, z coordinate data and using them in both virtual and LSM models. An upper body virtual model was needed to calculate the 3D torques about human joints for use in simulated lifting styles and to estimate the effect of external mechanical devices on human body. Firstly, the model had to be validated to be sure it provided accurate estimates of 3D moments in comparison to a previously validated LSM. Three synchronised Fastrak units with nine sensors were used to record data from one male subject who completed dynamic box lifting under 27 different load conditions (box weights (3), lifting techniques (3) and rotations (3)). The external moments about three axes of L4/L5 were compared for both models. A pressure switch on the box was used to denote the start and end of the lift. An excellent agreement [image omitted] was found between the two models for dynamic lifting tasks, especially for larger moments in flexion and extension. This virtual model was considered valid for use in a complete simulation of the upper body skeletal system. This biomechanical virtual model of the musculoskeletal system can be used by researchers and practitioners to give a better tool to study the causes of LBP and the effect of intervention strategies, by permitting the researcher to see and control a virtual subject's motions.     

Differences between measured and resultant joint moments during isometric contractions at the ankle joint

The purpose of this study was to examine two hypotheses: (a) during voluntary and electrically induced isometric contractions the moments measured at the dynamometer are different from the resultant moments in the same plane around the ankle joint and (b) at a given resultant moment during electrically induced isometric contractions the ankle angle while loading is different from the ankle angle while unloading. Twenty-seven long distance runners participated in the study. All subjects performed isometric maximal voluntary contractions (MVC) and contractions induced by electrostimulation at four different ankle-knee angle combinations on a Biodex-dynamometer. The kinematics of the leg were recorded using the vicon 624 system with eight cameras operating at 120 Hz. The main findings were: (a) the resultant moment at the ankle joint and the moment measured by the Biodex-dynamometer during isometric contractions are different, (b) during a plantar flexion effort the ankle angle changes significantly, whereas the knee angle shows only small and in most cases not significant changes, and (c) at identical resultant ankle joint moments the ankle angles are different between the loading and the unloading phases. The observed differences may lead to erroneous conclusions concerning the following: (a) diagnostic of muscle architecture, (b) estimation of the moment-ankle angle relationship and (c) estimation of the strain and hysteresis of tendons and aponeuroses.     

The influence of dynamic factors on triaxial net muscular moments at the L5/S1 joint during asymmetrical lifting and lowering.

Asymmetrical lifting and lowering are predominant activities in the workplace. Mechanical causes are suggested for many back injuries and the dynamic conditions within which spine loading occurs are related to spine loading increase. More data on tridimensional biomechanical lumbar spine loading during asymmetrical lifting and lowering are needed. A tridimensional dynamic multisegment model was developed to compute spinal loading for asymmetrical box-handling situations. The tridimensional positions of the anatomical markers were generated by a direct linear transformation algorithm adapted for the processing of data from two real and two virtual views (mirrors). Two force platforms measured the external forces. Five male subjects performed three variations (slow, fast and accelerated) of asymmetric lifting and two variations (slow and fast) of asymmetric lowering. The torsional, extension/flexion and lateral bending net muscular moments at the L5/S1 joint were computed and peak values selected for statistical analysis. For the lifting task, the fast and accelerated conditions showed significant increases over the slow condition for torsion, extension/flexion and lateral-bending moments. The accelerated condition also showed significant increases over the fast condition for extension. A comparison between lifting and lowering tasks showed equivalent loadings for torsion and extension. The moments were compared to average maximal values measured on equivalent male subject populations by isokinetic dynamometry. This showed torsional and extension values of 30 and 83% of the maximal possible subject capacity, respectively. These results demonstrated that dynamic factors do influence the load on the spine and highlighted the influence of both lifting and lowering on the loading of the spine. This suggested that for a more complete analysis of asymmetrical handling, the maximal velocity and acceleration produced during lifting should be included.     

Effects of vibration intensity on lower limb joint moments during standing

Muscle activity and joint moment of the lower limbs can provide different information about the stimulation of controlled whole-body vibration (CWBV) on human body. Previous studies investigated the immediate effects of the intensity of CWBV on enhancing lower-limb muscle activity. However, no study has examined the possible influence of CWBV intensity on joint loading. It remains unexplored how CWBV intensity impacts joint loading. This study was carried out (1) to quantify the effects of CWBV intensity in terms of vibration frequency and amplitude on the lower limb joint moments and (2) to examine the relationship between leg joint moments and vibration intensity characterized by the platform’s acceleration, that is determined by frequency and amplitude, during standing among young adults. Thirty healthy young adults participated in this study. Each participant experienced nine vibration intensity levels dependent upon the frequency (10, 20, and 30 Hz) and amplitude (1, 2, and 3 mm) while standing on a side-alternating vibration platform. Their body kinematics and vertical reaction forces between the feet and platform were collected. Inverse dynamics was employed to calculate the resultant moment for the ankle, knee, and hip joints in the sagittal plane. Our results revealed that the root-mean-square moment significantly increases with increasing vibration frequency or amplitude for all three joints. Further, all joint moments are strongly and positively correlated with the platform acceleration.     

Influence of IMU position and orientation placement errors on ground reaction force estimation

Wearable inertial measurement units (IMU) have been proposed to estimate GRF outside of specialized laboratories, however the precise influence of sensor placement error on accuracy is unknown. We investigated the influence of IMU position and orientation placement errors on GRF estimation accuracy. Methods: Kinematic data from twelve healthy subjects based on marker trajectories were used to simulate 1848 combinations of sensor position placement errors (range ± 100 mm) and orientation placement errors (range ± 25°) across eight body segments (trunk, pelvis, left/right thighs, left/right shanks, and left/right feet) during normal walking trials for baseline cases when a single sensor was misplaced and for the extreme cases when all sensors were simultaneously misplaced. Three machine learning algorithms were used to estimate GRF for each placement error condition and compared with the no placement error condition to evaluate performance. Results: Position placement errors for a single misplaced IMU reduced vertical GRF (VGRF), medio-lateral GRF (MLGRF), and anterior-posterior GRF (APGRF) estimation accuracy by up to 1.1%, 2.0%, and 0.9%, respectively and for all eight simultaneously misplaced IMUs by up to 4.9%, 6.0%, and 4.3%, respectively. Orientation placement errors for a single misplaced IMU reduced VGRF, MLGRF, and APGRF estimation accuracy by up to 4.8%, 7.3%, and 1.5%, respectively and for all eight simultaneously misplaced IMUs by up to 20.8%, 23.4%, and 12.3%, respectively. Conclusion: IMU sensor misplacement, particularly orientation placement errors, can significantly reduce GRF estimation accuracy and thus measures should be taken to account for placement errors in implementations of GRF estimation via wearable IMUs.     

Gait posture estimation using wearable acceleration and gyro sensors

A method for gait analysis using wearable acceleration sensors and gyro sensors is proposed in this work. The volunteers wore sensor units that included a tri-axis acceleration sensor and three single axis gyro sensors. The angular velocity data measured by the gyro sensors were used to estimate the translational acceleration in the gait analysis. The translational acceleration was then subtracted from the acceleration sensor measurements to obtain the gravitational acceleration, giving the orientation of the lower limb segments. Segment orientation along with body measurements were used to obtain the positions of hip, knee, and ankle joints to create stick figure models of the volunteers. This method can measure the three-dimensional positions of joint centers of the hip, knee, and ankle during movement. Experiments were carried out on the normal gait of three healthy volunteers. As a result, the flexion–extension (F–E) and the adduction–abduction (A–A) joint angles of the hips and the flexion–extension (F–E) joint angles of the knees were calculated and compared with a camera motion capture system. The correlation coefficients were above 0.88 for the hip F–E, higher than 0.72 for the hip A–A, better than 0.92 for the knee F–E. A moving stick figure model of each volunteer was created to visually confirm the walking posture. Further, the knee and ankle joint trajectories in the horizontal plane showed that the left and right legs were bilaterally symmetric.     

A fast estimation of biochemical oxygen demand using microbial sensors

Summary Microbial amperometric sensors for biochemical oxygen demand (BOD) determination using Bacillus subtilis or Trichosporon cutaneum cells immobilized in polyvinylalcohol have been developed. These sensors allow BOD measurements with very short response times (15–30s), a level of precision of ±5% and an operation stability of 30 days. A linear range was obtained for a B. subtilis-based sensor up to 20 mg/l BOD and for a T. cutaneum-based sensor up to 100 mg/l BOD using a glucose/glutamic acid standard.     

Relationship between moments at the L5/S1 level, hip and knee joint when lifting

A study was performed to determine the influence of load magnitude on the self selected technique of lifting. Specifically, it was hypothesized that with heavier weights a tendency would occur to lift more with the back and less with the legs. Flexion-extension moments at the L5/S1 level, hip and knee joints were calculated for subjects when lifting boxes weighing from 50 to 250 N. Lifts were performed using a freestyle technique at normal speed. The moment profiles (moment plotted vs time) were analyzed kinematically and as a function of the weight lifted. The kinematics of the lift changed as the weight increased. The moment at the L5/S1 level increased with increasing weight, however, the corresponding knee moment decreased. Thus, an inverse relationship was found between the moment at the L5/S1 level and the knee joint moment. An increase in weight lifted was also associated with an increase in the angular velocity at the knee while lifting. Apparently with heavier weights there is a tendency to extend the knees earlier during the lift than with lighter weights, confirming our hypothesis. This explains the reduced knee moment. Our findings lead to the hypothesis that quadriceps muscle strength limits the subjects' ability to lift with their knees flexed.