Tapping Into Skeletal Muscle Biomechanics for Design and Control of Lower Limb Exoskeletons: A Narrative Review.

Lower limb exoskeletons and exosuits ("exos") are traditionally designed with a strong focus on mechatronics and actuation, whereas the "human side" is often disregarded or minimally modeled. Muscle biomechanics principles and skeletal muscle response to robot-delivered loads should be incorporated in design/control of exos. In this narrative review, we summarize the advances in literature with respect to the fusion of muscle biomechanics and lower limb exoskeletons. We report methods to measure muscle biomechanics directly and indirectly and summarize the studies that have incorporated muscle measures for improved design and control of intuitive lower limb exos. Finally, we delve into articles that have studied how the human-exo interaction influences muscle biomechanics during locomotion. To support neurorehabilitation and facilitate everyday use of wearable assistive technologies, we believe that future studies should investigate and predict how exoskeleton assistance strategies would structurally remodel skeletal muscle over time. Real-time mapping of the neuromechanical origin and generation of muscle force resulting in joint torques should be combined with musculoskeletal models to address time-varying parameters such as adaptation to exos and fatigue. Development of smarter predictive controllers that steer rather than assist biological components could result in a synchronized human-machine system that optimizes the biological and electromechanical performance of the combined system.

Smoothness metrics for reaching performance after stroke. Part 1: which one to choose?

BACKGROUND: Smoothness is commonly used for measuring movement quality of the upper paretic limb during reaching tasks after stroke. Many different smoothness metrics have been used in stroke research, but a 'valid' metric has not been identified. A systematic review and subsequent rigorous analysis of smoothness metrics used in stroke research, in terms of their mathematical definitions and response to simulated perturbations, is needed to conclude whether they are valid for measuring smoothness. Our objective was to provide a recommendation for metrics that reflect smoothness after stroke based on: (1) a systematic review of smoothness metrics for reaching used in stroke research, (2) the mathematical description of the metrics, and (3) the response of metrics to simulated changes associated with smoothness deficits in the reaching profile. METHODS: The systematic review was performed by screening electronic databases using combined keyword groups Stroke, Reaching and Smoothness. Subsequently, each metric identified was assessed with mathematical criteria regarding smoothness: (a) being dimensionless, (b) being reproducible, (c) being based on rate of change of position, and (d) not being a linear transform of other smoothness metrics. The resulting metrics were tested for their response to simulated changes in reaching using models of velocity profiles with varying reaching distances and durations, harmonic disturbances, noise, and sub-movements. Two reaching tasks were simulated; reach-to-point and reach-to-grasp. The metrics that responded as expected in all simulation analyses were considered to be valid. RESULTS: The systematic review identified 32 different smoothness metrics, 17 of which were excluded based on mathematical criteria, and 13 more as they did not respond as expected in all simulation analyses. Eventually, we found that, for reach-to-point and reach-to-grasp movements, only Spectral Arc Length (SPARC) was found to be a valid metric. CONCLUSIONS: Based on this systematic review and simulation analyses, we recommend the use of SPARC as a valid smoothness metric in both reach-to-point and reach-to-grasp tasks of the upper limb after stroke. However, further research is needed to understand the time course of smoothness measured with SPARC for the upper limb early post stroke, preferably in longitudinal studies.

Smoothness metric during reach-to-grasp after stroke: part 2. longitudinal association with motor impairment.

BACKGROUND: The cause of smoothness deficits as a proxy for quality of movement post stroke is currently unclear. Previous simulation analyses showed that spectral arc length (SPARC) is a valid metric for investigating smoothness during a multi-joint goal-directed reaching task. The goal of this observational study was to investigate how SPARC values change over time, and whether SPARC is longitudinally associated with the recovery from motor impairments reflected by the Fugl-Meyer motor assessment of the upper extremity (FM-UE) in the first 6 months after stroke. METHODS: Forty patients who suffered a first-ever unilateral ischemic stroke (22 males, aged 58.6 ± 12.5 years) with upper extremity paresis underwent kinematic and clinical measurements in weeks 1, 2, 3, 4, 5, 8, 12, and 26 post stroke. Clinical measures included amongst others FM-UE. SPARC was obtained by three-dimensional kinematic measurements using an electromagnetic motion tracking system during a reach-to-grasp movement. Kinematic assessments of 12 healthy, age-matched individuals served as reference. Longitudinal linear mixed model analyses were performed to determine SPARC change over time, compare smoothness in patients with reference values of healthy individuals, and establish the longitudinal association between SPARC and FM-UE scores. RESULTS: SPARC showed a significant positive longitudinal association with FM-UE (B: 31.73, 95%-CI: [27.27 36.20], P < 0.001), which encompassed significant within- and between-subject effects (B: 30.85, 95%-CI: [26.28 35.41], P < 0.001 and B: 50.59, 95%-CI: [29.97 71.21], P < 0.001, respectively). Until 5 weeks post stroke, progress of time contributed significantly to the increase in SPARC and FM-UE scores (P < 0.05), whereafter they levelled off. At group level, smoothness was lower in patients who suffered a stroke compared to healthy subjects at all time points (P < 0.05). CONCLUSIONS: The present findings show that, after stroke, recovery of smoothness in a multi-joint reaching task and recovery from motor impairments are longitudinally associated and follow a similar time course. This suggests that the reduction of smoothness deficits quantified by SPARC is a proper objective reflection of recovery from motor impairment, as reflected by FM-UE, probably driven by a common underlying process of spontaneous neurological recovery early post stroke.

Portable Gait Lab: Estimating Over-Ground 3D Ground Reaction Forces Using Only a Pelvis IMU.

As an alternative to force plates, an inertial measurement unit (IMU) at the pelvis can offer an ambulatory method for measuring total center of mass (CoM) accelerations and, thereby, the ground reaction forces (GRF) during gait. The challenge here is to estimate the 3D components of the GRF. We employ a calibration procedure and an error state extended Kalman filter based on an earlier work to estimate the instantaneous 3D GRF for different over-ground walking patterns. The GRF were then expressed in a body-centric reference frame, to enable an ambulatory setup not related to a fixed global frame. The results were validated with ForceShoesTM, and the average error in estimating instantaneous shear GRF was 5.2 ± 0.5% of body weight across different variable over-ground walking tasks. The study shows that a single pelvis IMU can measure 3D GRF in a minimal and ambulatory manner during over-ground gait.

Phytochemical analysis of Convolvulus hystrix Vahl and its biological effects in rats.

"Convolvulus hystrix Vahl" is a plant that has been known to Ancient Egyptians and to Arabs and its root was used traditionally as a purgative. Our attention was directed to the root bark as we observed that the largest part of the plant is deeply impeded underground. The work plan involved testing experimental animals for the influence of aqueous root bark extract on carbohydrate, fat and protein metabolisms as reflected on the growth and relevant laboratory metabolic assessment parameters. Proximate analysis showed high percentages of moisture (85%) and total lipids (7.2%) and surprising amounts of elements such as barium, strontium, rhodium and tellurium (1.7 mg, 3.1 mg, 8 mg and 9.1 mg/g ash, respectively). Random serum glucose value showed a significant decrease in the treated female group (p < 0.05). Serum total proteins of treated female group were found to be increased significantly (p < 0.001), while it was found to be decreased in the relevant treated male group (p < 0.01), together with a significant decrease in blood urea nitrogen (p < 0.05), with a significant increase in the serum creatinine (p < 0.05). Concerning serum fat metabolic parameters, a significant decrease in the serum triglycerides and high-density lipoproteins (p < 0.01 and p < 0.01, respectively) were found. We concluded that the presence of huge amount of polyphenolics such as tannins is responsible for the overall results documented as growth retarding and antinutritional factors. The results were motivating and pointed out to the possible opening of vast areas of research in the field of natural products. We recommend a series of biochemical and pharmacological studies concerning different parts of the plant as well.

Electromyography-driven musculoskeletal models with time-varying fatigue dynamics improve lumbosacral joint moments during lifting.

Muscle fatigue is prevalent across different aspects of daily life. Tracking muscle fatigue is useful to understand muscle overuse and possible risk of injury leading to musculoskeletal disorders. Current fatigue models are not suitable for real-world settings as they are either validated using simulations or non-functional tasks. Moreover, models that capture the changes to muscle activity due to fatigue either assume a linear relationship between muscle activity and muscle force or utilize a simple muscle model. Personalised electromygraphy (EMG)-driven musculoskeletal models (pEMS) offer person-specific approaches to model muscle and joint kinetics during a wide repertoire of daily life tasks. These models utilize EMG, thus capturing central fatigue-dependent changes in multi-muscle bio-electrical activity. However, the peripheral muscle force decay is missing in these models. Thus, we studied the influence of fatigue on a large scale pEMS of the trunk. Eleven healthy participants performed functional asymmetric lifting task. Average peak body-weight normalized lumbosacral moments (BW-LM) were estimated to be 2.55 ± 0.26 Nm/kg by reference inverse dynamics. After complete exhaustion of the lower back, the pEMS overestimated the peak BW-LM by 0.64 ± 0.37 Nm/kg. Then, we developed a time-varying muscle force decay model resulting in a time-varying pEMS (t-pEMS). This reduced the difference between BW-LM estimated by the t-pEMS and reference to 0.49 ± 0.14 Nm/kg. We also showed that five fatiguing contractions are sufficient to calibrate the t-pEMS. Thus, this study presents a person and muscle specific model to track fatigue during functional tasks.

Benchmarking commercially available soft and rigid passive back exoskeletons for an industrial workplace.

Low-back pain is a common occupational hazard for industrial workers. Several studies show the advantages of using rigid and soft back-support passive exoskeletons and exosuits (exos) to reduce the low-back loading and risk of injury. However, benefits of using these exos have been shown to be task-specific. Therefore, in this study, we developed a benchmarking approach to assess exos for an industrial workplace at Hankamp Gears B.V. We assessed two rigid (Laevo Flex, Paexo back) and two soft (Auxivo Liftsuit 1.0, and Darwing Hakobelude) exos for tasks resembling the workplace. We measured the assistive moment provided by each exo and their respective influence on muscle activity as well as the user's perception of comfort and exertion. Ten participants performed four lifting tasks (Static hold, Asymmetric, Squat, and Stoop), while their electromyography and subjective measures were collected. The two rigid exos provided the largest assistance during the Dynamic tasks. Reductions in erector spinae activity were seen to be task-specific, with larger reductions for the two rigid exos. Overall, Laevo Flex offered a good balance between assistive moments, reductions in muscle activity, as well as user comfort and reductions in perceived exertion. Thus, we recommend benchmarking exos for intended use in the industrial workplace. This will hopefully result in a better adoption of the back-support exoskeletons in the workplace and help reduce low-back pain.

Machine learning and analytic hierarchy process integration for selecting a sustainable tractor.

Selecting the appropriate tractor for small-scale farms is a complex process due to the multitude of technical, environmental, and economic criteria that must be evaluated. This study addresses this challenge by integrating the Analytic Hierarchy Process (AHP) with machine learning (ML) to reduce the number of criteria and simplify the decision-making process. The research aims to determine the most relevant criteria aligned with sustainable development goals for selecting the right tractor, focusing on small farms in the Egyptian Delta. Four tractors, with horsepower ranging from 55 to 95, were evaluated based on inputs from forty-two governmental service providers in the study area. Initially, nine criteria were identified, encompassing key technical, environmental, and economic factors. These criteria were reduced to three-price, power, and maintenance costs by weights 0.142, 0.334, and 0.525, respectively-using Hierarchical Agglomerative Clustering with Euclidean distance. This reduction streamlined the selection process, making it more practical for farmers. Results show that the second tractor (T2), with a priority score of 0.326 and a normalized value of 33.4%, emerged as the optimal choice for small-scale farmers, outperforming the first tractor (T1) (28.7%) and third tractor (T3) (21%). Integrating AHP and ML simplifies tractor selection, ensuring sustainability, cost-efficiency, and operational effectiveness.

FibroScan as a surveillance marker post-cavopulmonary anastomosis for single-ventricle physiology.

Purpose: Single-ventricle physiology encompasses a group of congenital cardiac malformations with only one functional ventricle. The Fontan procedure is the final palliation of this pathway and has its complications. One of these is Fontan-associated liver disease (FALD). It is known that all patients with Fontan will have FALD, due to the physiology of the Fontan circuit, and only the severity will vary. The pathophysiology of hepatic damage in FALD is unique and not easily detectable by routine non-invasive investigations. Therefore, this study is aimed to identify if FibroScan can be used as a surveillance marker to detect and assess the progression of FALD. Methods: Patients who attended the Cardiothoracic and Vascular Surgery Outpatient Department (OPD) for follow-up post-cavopulmonary anastomosis (bidirectional Glenn and Fontan) were enrolled in this study. They underwent routine examinations and tests, and in addition a FibroScan was performed. Results: FibroScan showed that the liver stiffness measurement (LSM) was increased in all patients who had undergone Fontan and a couple of patients who had undergone bidirectional (BD) Glenn. The LSM was 12.29 (± 3.59) kPa in patients post-Fontan and 6.64 (± 4.24) kPa in patients post-BD Glenn. This raised LSM was not associated with a parallel rise in liver enzymes or other laboratory markers associated with liver function. This emphasizes the suitability of FibroScan as an early and non-invasive surveillance tool for monitoring the progression of hepatic venous congestion and FALD. Conclusion: We have found that LSM via FibroScan can effectively be a surveillance or screening test for FALD. Serial FibroScans can be used to monitor the progress of liver disease. Raised LSM may also have a role in predicting the morbidity for completion of Fontan post-BD Glenn operation. Large-scale studies are needed to validate our findings.

Gradual correction of idiopathic genu varum deformity using the Ilizarov technique.

PURPOSE: Proximal tibial osteotomy is an effective treatment option for genu varum deformity among the many other described techniques. The purpose of this study is to evaluate the clinical and radiological outcomes and the complications in gradual correction of idiopathic genu varum deformity using Ilizarov frame. METHODS: Proximal tibial medial opening wedge osteotomy was performed in 21 lower limbs of 11 patients, with whom the Ilizarov external fixator was used for gradual correction of the varus deformity. The mean age of the patients was 24.8 years (SD, 5.3). Deformity measurements of conventional mechanical axis deviation, mechanical medial proximal tibial angle, mechanical lateral distal femoral angle, posterior proximal tibial angle, joint conversion angle, tibio-femoral angle and tibial slope were compared. RESULTS: The mean time for removal of the Ilizarov fixator was 24.7 weeks. At the last follow-up, the mean of Hospital for Special Surgery knee score increased, and the mean mechanical medial proximal tibial angle, tibio-femoral angle and conventional mechanical axis deviation improved. The differences between preoperative and postoperative posterior proximal tibial angle, mechanical lateral distal femoral angle, joint conversion angle and tibial slope were not significant. Ten complications were observed, of which 8 were minor complications and 2 were minor complications. CONCLUSION: With a few complications, normal alignment and orientation of lower extremity can be established in patients with idiopathic genu varum deformity through gradual correction using a Ilizarov fixator. LEVEL OF EVIDENCE: Retrospective case series, Level IV.

A Neuromechanical Model-Based Strategy to Estimate the Operator's Payload in Industrial Lifting Tasks.

One of the main technological barriers hindering the development of active industrial exoskeleton is today represented by the lack of suitable payload estimation algorithms characterized by high accuracy and low calibration time. The knowledge of the payload enables exoskeletons to dynamically provide the required assistance to the user. This work proposes a payload estimation methodology based on personalized Electromyography-driven musculoskeletal models (pEMS) combined with a payload estimation method we called "delta torque" that allows the decoupling of payload dynamical properties from human dynamical properties. The contribution of this work lies in the conceptualization of such methodology and its validation considering human operators during industrial lifting tasks. With respect to existing solutions often based on machine learning, our methodology requires smaller training datasets and can better generalize across different payloads and tasks. The proposed payload estimation methodology has been validated on lifting tasks with 0kg, 5kg, 10kg and 15kg, resulting in an average MAE of about 1.4 Kg. Even if 5kg and 10Kg lifting tasks were out of the training set, the MAE related to these tasks are 1.6 kg and 1.1 kg, respectively, demonstrating the generalizing property of the proposed methodology. To the best of the authors' knowledge, this is the first time that an EMG-driven model-based approach is proposed for human payload estimation.

Flat micro heat pipe-based shell and tube storage unit for indirect solar dryer: a pilot study.

Poria cocos has been dried in an indirect solar drying system composed of a roughened solar air heater (RSAH), a shell and tube storage unit assisted with flat micro heat pipes fins, and a drying chamber. The main novelty in this study is using FMHPs as fins in shell and tube storage unit with paraffin wax and lack of investigations on Poria cocos solar drying as medicinal material used in Chinese medicine. First and second laws of thermodynamics are used to assess the performance of the system and the results indicated that the RSAH average thermal ([Formula: see text]) and exergy efficiency ([Formula: see text]) were 73.9% and 5.1%, respectively, with averaged incident solar radiation of 671 W/m2 under airflow rate of 0.0381 m3/s. Furthermore, the storing system showed 37.6% as averaged overall [Formula: see text] and 17.2% as averaged overall [Formula: see text], as well as, discharging prolonged to 4 h with effective drying temperature. The overall [Formula: see text] of the dryer was 27.6% with specific energy consumption (SEC) of 8.629 kWh/kg moisture. The payback period of the system is 1.7 years.

Does a Soft Actuated Back Exosuit Influence Multimodal Physiological Measurements and User Perception During an Industry Inspired Task?

Back support soft exosuits are promising solutions to reduce risk of musculoskeletal injuries at workplaces resulting from physically demanding and repetitive lifting tasks. Design of novel active exosuits address the impact on the muscle activity and metabolic costs but do not consider other critical aspects such as comfort and user perception during the intended tasks. Thus, in this study, we describe a novel soft active exosuit in line with its impact on physiological and subjective measures during lifting. We tested four healthy participants who performed repetitive lifting tasks with and without this exosuit. The exosuit provided assistance proportional to the lumbar flexion angle measured using an inertial measurement unit. We measured the participant's multimodal physiological measures including surface electromyography, metabolic cost, heart rate, and skin temperature. We also measured subjective scores on user exertion, task load, and device acceptability. All participants perceived a reduction in task load when using the exosuit. Three participants showed reduction of muscle activity for the erector spinae muscles. The metabolic costs and heart rate reserve reduced for two participants, with similar trends for skin temperature. For future development of workplace exosuits, we recommend incorporating assessments of both physiological and subjective measures, considering the user-dependent response to the exosuit.

Does short-term application of an Ilizarov frame with transfixion pins correct relapsed clubfoot in children?

BACKGROUND: Treatment of relapsed clubfoot after soft tissue release in children is difficult because of the high recurrence rate and related complications. Even though the Ilizarov method is used for soft tissue distraction, there is a high incidence of recurrence after removal of the Ilizarov frame owing to previous contracture of soft tissue and a skin scar. QUESTIONS/PURPOSES: We asked (1) whether transfixation of midfoot joints by temporary K wires during the consolidation stage after short-term application of an Ilizarov frame would maintain correction of the relapsed clubfoot clinicoradiologically and (2) whether this method would reduce the rate of recurrence and related complications in patients with a skin scar from previous surgery. METHODS: We retrospectively reviewed 18 patients (19 feet) with relapsed clubfeet who underwent correction by soft tissue distraction using an Ilizarov ring fixator, between March 2005 and June 2008. The mean age of the patients was 8 ± 2 years (range, 4-15 years). K wire fixation for the midfoot joints combined with a below-knee cast were used during the consolidation stage. The minimum followup was 2 years (mean, 4.5 years; range, 2-6 years). RESULTS: The average duration of frame application was 5 weeks; the mean duration of treatment was 11 weeks. At last followup, 16 of 19 feet were painless and plantigrade and only three of 19 feet had recurrence. The mean preoperative clinical American Foot and Ankle Society (AOFAS) score had increased at last followup (57 versus 81). The values of the AP talocalcaneal, AP talo-first metatarsal, and lateral calcaneo-first metatarsal angles improved after treatment. The three recurrent clubfeet were treated by corrective osteotomies and Ilizarov frame application. CONCLUSION: This method could maintain the correction of relapsed clubfoot in children and reduce the recurrence rate and complications regardless of the presence of a skin scar owing to previous surgery.

Centroidal Moment Pivot for ambulatory estimation of relative feet and CoM movement post stroke: Portable Gait Lab.

Measuring gait and balance recovery is necessary post stroke. In an earlier study, we developed a minimal three Inertial Measurement Units (IMUs) system called Portable Gait Lab (PGL). The PGL used the Centroidal Moment Pivot (CMP) assumption to estimate relative foot and centre of mass (CoM) positions, and thereby estimate gait parameters in healthy participants. In this study, we validate the feasibility of the PGL to track foot and CoM trajectory during gait in four persons with chronic stroke. Spatiotemporal gait and balance measures were estimated from the foot and CoM trajectories, and compared with the reference ForceShoes™. Each participant made at least 20 steps, and the PGL was able to track foot and CoM trajectories with a root mean square of the differences with the reference of 2.9 ± 0.2 cm and 4.6 ± 3.6 cm. The distances between either foot at the end of the walking task, and step lengths were estimated by PGL with an average error with the reference of 1.98 ± 2.2 cm and 7.8 ± 0.1 cm respectively across participants. We show that our approach was able to estimate spatiotemporal and balance parameters related to gait quality in a clinically useful manner. We recommend conducting further studies to study the feasibility of using the PGL system for variable gait patterns measured post stroke.

Portable Gait Lab: Tracking Relative Distances of Feet and CoM Using Three IMUs.

Ambulatory estimation of gait and balance parameters requires knowledge of relative feet and centre of mass (CoM) positions. Inertial measurement units (IMU) placed on each foot, and on the pelvis are useful in tracking these segments over time, but cannot track the relative distances between these segments. Further, drift due to strapdown inertial navigation results in erroneous relative estimates of feet and CoM positions after a few steps. In this study, we track the relative distances using the assumptions of the Centroidal Moment Pivot (CMP) theory. An Extended Kalman filter approach was used to fuse information from different sources: strapdown inertial navigation, commonly used constraints such as zero velocity updates, and relative segment distances from the CMP assumption; to eventually track relative feet and CoM positions. These estimates were expressed in a reference frame defined by the heading of each step. The validity of this approach was tested on variable gait. The step lengths and step widths were estimated with an average absolute error of 4.6±1.5 cm and 3.8±1.5 cm respectively when compared against the reference VICON©. Additionally, we validated the relative distances of the feet and the CoM, and further, show that the approach proves useful in identifying asymmetric gait patterns. We conclude that a three IMU approach is feasible as a portable gait lab for ambulatory measurement of foot and CoM positions in daily life.

Portable Gait Lab: Estimating 3D GRF Using a Pelvis IMU in a Foot IMU Defined Frame.

Ground Reaction Forces (GRF) during gait are measured using expensive laboratory setups such as in-floor or treadmill force plates. Ambulatory measurement of GRF using wearables enables remote monitoring of gait and balance. Here, we propose using an Inertial Measurement Unit (IMU) mounted on the pelvis to estimate the GRF during gait in daily life. Calibration procedures and an Error State Extended Kalman filter (EEKF) were used to transform the accelerations at the center of mass (CoM) to the 3D GRF. The instantaneous 3D GRF was estimated for different overground walking patterns and compared with the 3D GRF measured using the reference ForceShoe™ system. Furthermore, we introduce a changing reference frame called the current step frame that followed the direction of each step made. The frame was defined using movement of the feet, and the estimated GRF were expressed in this new frame. This allowed direct comparison and validation with the reference. The mean and standard deviation of error between the estimated instantaneous 3D GRF and the reference, normalized against the range of the reference, was 12.1 ± 3.3% across all walking tasks, in the horizontal plane. The error margins show that a single pelvis IMU could be a minimal and ambulatory sensing alternative for estimating the instantaneous 3D components of GRF during overground gait.

Gait and Dynamic Balance Sensing Using Wearable Foot Sensors.

Remote monitoring of gait performance offers possibilities for objective evaluation and tackling impairment in motor ability, gait, and balance in populations, such as elderly, stroke, multiple sclerosis, and Parkinson's. This requires a wearable and unobtrusive system capable of estimating ambulatory gait and balance measures, such as the extrapolated center of mass (XCoM) and dynamicmargin of stability. These estimations require the knowledge of 3-D forces and moments (F&M) and accurate foot positions. Though an existing ambulatory gait and balance system (AGBS) consisting of 3-D F&M sensors and inertial measurement units can be used for the purpose, it is bulky and conspicuous. Resistive pressure sensorswere investigated as an alternative to the onboard 3-D F&M sensors. Subject-specific regression models were built to estimate 3-D F&M from 1-D plantar pressures. The model was applicable for different walking speeds. Different pressure sensor configurations were studied to optimize the system complexity and accuracy. Using resistive sensors only under the toe and heel, we were able to estimate the XCoM with a mean absolute rms error of 2.2 ±0.3 cm in the walking direction while walking at a preferred speed, when compared to the AGBS. For the same case, the XCoM was classified as ahead or behind the base of support correctly at 97.7±1.7%. In conclusion, this paper shows that pressure sensors, minimally under the heel and toe, offer a lightweight and inconspicuous alternative for F&M sensing, toward estimating ambulatory gait and dynamic balance.

Portable Gait Lab: Zero Moment Point for Minimal Sensing of Gait.

Ambulatory sensing of gait kinematics using inertial measurement units (IMUs) usually uses sensor fusion filters. These algorithms require measurement updates to reduce drift between segments. A full body IMU suit can use biomechanical relations between body segments to solve this. However, when minimising the sensor set, we lose a lot of this information. In this study, we explore the assumptions of zero moment point (ZMP) as a possible source of measurement updates for the sensor fusion filters. ZMP is otherwise utilised for humanoid gait in robots. In this study, first, the relation between the ZMP and centre of pressure (CoP) is studied using a GRAIL system, consisting of opto-kinetic measurements. We find that the mean distance over the gait cycle between ZMP and CoP is 10.5±1.2% of the foot length. Following this, we show how these results could be used to improve measurements in a minimal IMU based sensing setup.