Eveline Graf

The shifting of the torsion axis of the foot during the stance phase of lateral cutting movements

Previously, foot torsion has been studied with respect to peak angles during athletic movements. Athletic footwear often contains a torsion element that dictates a torsion axis of the shoe. The location of the axis of rotation of the foot is, however, unknown. Therefore, the purpose of this study was to describe the torsion axis location during the stance phase of lateral cutting movements. Thirty-nine subjects performed a barefoot lateral jab and 19 subjects performed a barefoot shuffle cut. Markers were placed on the fore- and rearfoot and their movement was quantified using a 3-D video system. The torsion axis location was determined using a modified finite helical axis approach during the stance phase while the torsion angle was calculated as the amount of rotation around the torsion axis. At the beginning of the stance phase, the axis was located on the medial aspect of the foot. During the stance phase, the axis shifted towards the lateral side of the foot before the axis moved back to the medial aspect of the foot at the end of stance. For both movements significant correlations between the axis location in the vertical and medio-lateral directions and the torsion angle were found. With larger torsion (forefoot inversion) angles the axis was in a more lateral and plantar location within the foot. With this knowledge, a shoe torsion system where the shoe torsion axis location is in agreement with the foot axis location could be developed.

Effect of Relative Marker Movement on the Calculation of the Foot Torsion Axis Using a Combined Cardan Angle and Helical Axis Approach

The two main movements occurring between the forefoot and rearfoot segment of a human foot are flexion at the metatarsophalangeal joints and torsion in the midfoot. The location of the torsion axis within the foot is currently unknown. The purpose of this study was to develop a method based on Cardan angles and the finite helical axis approach to calculate the torsion axis without the effect of flexion. As the finite helical axis method is susceptible to error due to noise with small helical rotations, a minimal amount of rotation was defined in order to accurately determine the torsion axis location. Using simulation, the location of the axis based on data containing noise was compared to the axis location of data without noise with a one-sample t-test and Fishers combined probability score. When using only data with helical rotation of seven degrees or more, the location of the torsion axis based on the data with noise was within 0.2 mm of the reference location. Therefore, the proposed method allowed an accurate calculation of the foot torsion axis location.

Evaluation of a passive exoskeleton for static upper limb activities

The aim of this study was to evaluate the effect of a passive upper body exoskeleton on muscle activity, perceived musculoskeletal effort, local perceived pressure and subjective usability for a static overhead task. Eight participants (4 male, 4 female) held a load (0 kg and 2 kg) three times overhead for a duration of 30 s each, both with and without the exoskeleton. Muscle activity was significantly reduced for the Biceps Brachii (49%) and Medial Deltoid (62%) by the device for the 2 kg load. Perceived effort of the arms was significantly lower with the device for the 2 kg load (41%). The device did not have a significant effect on trunk or leg muscle activity (for the 2 kg load) or perceived effort. Local perceived pressure was rated below 2 (low pressure levels) for all contact areas assessed. Half of the participants rated the device usability as acceptable. The exoskeleton reduced muscle activity and perceived effort by the arms, and had no significant negative effect on the trunk and lower body with regards to muscle activity, perceived effort and localised discomfort.

Between-day reliability of three-dimensional motion analysis of the trunk: A comparison of marker based protocols

Motion capture of the trunk using three-dimensional optoelectronic systems and skin markers placed on anatomical landmarks is prone to error due to marker placement, thus decreasing between-day reliability. The influence of these errors on angular output might be reduced by using an overdetermined number of markers and optimization algorithms, or by defining the neutral position using a reference trial. The purpose of this study was to quantify and compare the between-day reliability of trunk kinematics, when using these methods. In each of two sessions, 20 subjects performed four movement tasks. Trunk kinematics were established through the plug-in-gait protocol, the point cloud optimization algorithm, and by defining upright standing as neutral position. Between-day reliability was analyzed using generalizability theory and quantified by indexes of dependability. Across all movement tasks, none of the methods was superior in terms of between-day reliability. The point cloud algorithm did not improve between-day reliability, but did result in 24.3% greater axial rotation angles. The definition of neutral position by means of a reference trial revealed 5.8% higher indexes of dependability for lateral bending and axial rotation angles, but 13.7% smaller indexes of dependability for flexion angles. Further, using a reference trial resulted in 8.3° greater trunk flexion angles. Therefore, the selection of appropriate marker placement and the corresponding calculation of angular output are dependent on the movement task and the underlying research question.

Energy Efficiency Analysis and Design Optimization of an Actuation System in a Soft Modular Lower Limb Exoskeleton

One of the critical aspects in the design of an assistive wearable robot is the energy efficiency of the actuation system, since it significantly affects the weight and consequently the comfort of the system. Several strategies have been used in previous research, mostly based on energy harvesting, compliant elements for mechanical energy accumulation (springs or elastic cords), ratchets, and clutches. However, the design of the optimal actuator arrangement is highly dependent on the task, which increases significantly the complexity of the design process. In this letter, we present an energy efficiency analysis and design optimization of an actuation system applied to a soft module lower limb exoskeleton. Instead of performing a comparison between predefined mechanism arrangements, we solve a full optimization problem that includes not only the mechanism parameters, but also the mechanism architecture itself. The optimization is performed for a walking task using gait data from a stroke subject, and the result is a set of actuator arrangements with optimal parameters for the analyzed task and selected user. The optimized mechanism is able to reduce the energy requirements by 20–65%, depending on the joint. The proposed mechanism is currently under development within the XoSoft EU project, a modular soft lower-limb exoskeleton to assist people with mobility impairments.

The effect of footwear torsional stiffness on lower extremity kinematics and kinetics during lateral cutting movements

Purpose: Footwear torsional stiffness affects ankle kinematics during cutting movements. The influence of torsional stiffness on lower extremity kinetics has not been studied. It was hypothesised that footwear with high torsional stiffness increases the ankle eversion, knee abduction and internal rotation moments in cutting movements. Methods: Nineteen participants performed seven repetitions of a lateral jab and a shuffle cut in two shoes with different torsional stiffness. Markers placed on forefoot, rearfoot and shank of the right leg were used to determine the kinematics. Simultaneous recordings of the ground reaction forces allowed the calculation of ground reaction impulses and internal joint moments using an inverse dynamics approach. Results: Peak torsion angles (frontal plane rotation between fore- and rearfoot) were reduced in the torsional stiff shoe (shuffle cut: 22.0° vs. 18.5°, p < 0.001; lateral jab: 22.8° vs. 20.1°, p = 0.020 flexible vs. stiff shoe). For the shuffle cut, the peak ankle eversion moment (52.9 Nm vs. 63.0 Nm, p = 0.003) and inversion angle (25.9° vs. 28.5°, p < 0.001) were higher in the stiff shoe. For the lateral jab no differences between footwear were found for the ankle kinematics or kinetics. No differences between footwear were found for knee kinematics. The ground reaction impulses were not different between shoes. Conclusions: Increased footwear torsional stiffness causes higher ankle eversion moments which may increase the risk for ankle injuries. Knee moments were not affected by footwear torsional stiffness; therefore, footwear torsional stiffness seems to have no effect on the risk for anterior cruciate ligament (ACL) injuries.

The effect of lateral banking on the kinematics and kinetics of the lower extremity during lateral cutting movements

There are many aspects of cutting movements that can limit performance, however, the implementation of lateral banking may reduce some of these limitations. Banking could provide a protective mechanism, placing the foot and ankle in orientations that keep them out of dangerous positions. This study sought to determine the effect of two banking angles on the kinematics and kinetics of the lower extremity during two athletic maneuvers. Kinematic and kinetic data were collected on 10 recreational athletes performing v-cuts and side shuffle movements on different banked surfaces (0°, 10°, 20°). Each sample surface was rigidly attached to the force platform. Joint moments were calculated and compared between conditions using a repeated measures ANOVA. Banking had a pronounced effect on the ankle joint. As banking increased, the amount of joint loading in the transverse and frontal planes decreased likely leading to a reduction in injury risk. Also an increase in knee joint loading in the frontal plane was seen during the 20° bank during the v-cut. Conversely loading in the sagittal plane at the ankle joint increased with banking and coupled with a reorientation of the ground reaction vector may facilitate a performance increase. The current study indicates that the 10° bank may be the optimal bank, in that it decreases ankle joint loading, as well as increases specific performance variables while not increasing frontal plane knee joint loading. If banking could be incorporated in footwear it may be able to provide a protective mechanism for athletes.

The effect of shoe torsional stiffness on lower extremity kinematics and biomechanical risk factors for patellofemoral pain syndrome during running

Objective: The effect of footwear torsional stiffness on lower extremity biomechanics is not well known, although there are indications that it could affect rearfoot and ankle kinematics. These variables have previously been linked to the development of patellofemoral pain syndrome (PFPS) in runners. Therefore, the aim of this study was to compare the rearfoot and ankle frontal plane kinematics and knee abduction angular impulse between shoes with different torsional stiffness during running. Methods: Nineteen experienced runners performed heel-toe running at 3.7 m s−1 in three running shoes with different torsional stiffness. Using surface-mounted markers and a force plate, the kinematics and kinetics of the rearfoot, ankle and knee were measured. Torsion, rearfoot and ankle eversion, tibial rotation, knee abduction impulse, and vertical ground reaction force (GRF) peak were compared between footwear conditions using repeated-measures ANOVA. Results: The torsion angle was significantly different between shoes but none of the other variables showed a difference between conditions. Focusing only on the part of the stance phase with forefoot–ground contact, significant differences were reported in the range of motion (ROM) of rearfoot and ankle eversion. The differences in torsional stiffness of the running shoes did not alter the rearfoot/ankle kinematics or the knee angular impulse, which are variables that have been described as risk factors for PFPS. Conclusions: During heel-toe running, the shoe torsional stiffness does not seem to have an effect on the injury risk for PFPS. However, there are indications that, for movements performed mainly on the forefoot, this shoe characteristic could have relevance.

Effect of torsional stiffness on biomechanical variables of the lower extremity during running

Torsion, the relative in-/eversion between forefoot and rearfoot, is a concept that has been incorporated into running shoes for almost 30 years. Studies have shown an influence of footwear torsional stiffness on lower extremity biomechanics during running but results are inconclusive. However, the influence of the torsion axis of the shoe on kinematics and kinetics of running has not been examined. Therefore, the goal was to examine the effect of shoes with a specially designed torsion element on running biomechanics of the lower extremities. Twenty runners performed heel–toe running at 4.0 ms−1 with three shoes and barefoot. All shoes had a torsion element based on a rearfoot and a forefoot element connected by bushings that had a defined rotation axis. The torsional stiffness was altered by modifications made to the torsion element and the surrounding midsole. A force plate and camera system were used to collect kinetics and kinematics. Foot torsion, ankle eversion, ankle and knee moments in the frontal and transverse plane and ground reaction forces were compared between conditions using paired t-tests. The shoe with the lowest torsional stiffness did not result in larger torsion range of motion compared to a stiffer shoe. Ankle eversion decreased with decreasing torsional stiffness while the changes in ankle kinetics were not consistent between the frontal and transverse plane. Torsional stiffness did not have a systematic influence on knee joint kinetics. While shoe torsional stiffness influences foot kinematics significantly, it does not affect lower extremity running biomechanics in a way that would alter the risk of running injuries.

Basic functionality of a prototype wearable assistive soft exoskeleton for people with gait impairments: a case study

XoSoft is a soft modular wearable assistive exoskeleton for people with mild to moderate gait impairments. It is currently being developed by a European Consortium (www.xosoft.eu) and aims to provide tailored and active lower limb support during ambulation. During development, user-centered design principles were followed in parallel with the aim of providing functional support during gait. A prototype was developed and was tested for practicability, usability, comfort and assistive function (summarized as basic functionality) with a potential end user. The prototype consisted of a garment, electromagnetic clutch-controlled elastic bands supporting knee- and hip flexion and a backpack containing the sensor and actuator control of the system. The participant had experienced a stroke and presented with unilateral impairment of the lower and upper extremities. In testing, he donned and doffed the prototype independently as far as possible, and performed walking trials with the system in both active (powered on) and passive (powered off) modes. Afterwards, the participant rated the perceived pressure and various elements of usability. Results highlighted aspects of the system for improvement during future phases of XoSoft development, and also identified useful aspects of prototype design to be maintained. The basic functionality of XoSoft could be assumed as satisfactory given that it was the first version of a working prototype. The study highlights the benefits of this participatory evaluation design approach in assistive soft robotics development.