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Purpose To determine how sex and fatigue affect lower limb kinematics, kinetics, and muscle activity during unanticipated side-step cutting. Methods Twenty-three physically active subjects (men 11, women 12) performed 10 successful trials of cutting manoeuvres each to either side under unanticipated conditions in response to 2 light emitting diodes before and after fatigue conditions. Data were analysed and compared regarding sex and fatigue conditions using two-way repeated measures analysis of variance. Results After fatigue-inducing exercise, women demonstrated larger impulses of ground reaction force (IGRF) during the first 50 ms (2.4 ± 0.8 vs. 2.1 ± 0.9, P  < 0.05) than did men. Significant primary effects of sex indicated that women showed a smaller hip flexion angle at initial contact (40.4 ± 6.9° vs. 49.7 ± 9.1°, P  < 0.05) and at maximum flexion angle (41.3 ± 7.7° vs. 51.4 ± 9.0°, P  < 0.05) compared with men. Significant primary effects of fatigue were observed in the gluteus maximus muscle during 50 ms before initial contact (+21.5 ± 48.3 %, P  < 0.05) and in the semimembranosus muscle during 50 ms before initial contact (−6.2 ± 20.1 %, P  < 0.05) and the first 50 ms of side-step cutting (−7.9 ± 26.6 %, P  < 0.05). Conclusions Our results suggest that sex differences, especially larger IGRF in a fatigue state combined with less hip flexion angle, lead to women having a higher risk for anterior cruciate ligament (ACL) injury. These findings may contribute to understanding the underlying mechanism of injury and development of preventive exercises against ACL injury. Level of evidence Prospective comparative study, Level II.

Lower-limb wearable robotic devices can improve clinical gait and reduce energetic demand in healthy populations. To help enable real-world use, we sought to examine how assistance should be applied in variable gait conditions and suggest an approach derived from knowledge of human locomotion mechanics to establish a 'roadmap' for wearable robot design. We characterized the changes in joint mechanics during walking and running across a range of incline/decline grades and then provide an analysis that informs the development of lower-limb exoskeletons capable of operating across a range of mechanical demands. We hypothesized that the distribution of limb-joint positive mechanical power would shift to the hip for incline walking and running and that the distribution of limb-joint negative mechanical power would shift to the knee for decline walking and running. Eight subjects (6M,2F) completed five walking (1.25 m s-1) trials at -8.53°, -5.71°, 0°, 5.71°, and 8.53° grade and five running (2.25 m s-1) trials at -5.71°, -2.86°, 0°, 2.86°, and 5.71° grade on a treadmill. We calculated time-varying joint moment and power output for the ankle, knee, and hip. For each gait, we examined how individual limb-joints contributed to total limb positive, negative and net power across grades. For both walking and running, changes in grade caused a redistribution of joint mechanical power generation and absorption. From level to incline walking, the ankle's contribution to limb positive power decreased from 44% on the level to 28% at 8.53° uphill grade (p < 0.0001) while the hip's contribution increased from 27% to 52% (p < 0.0001). In running, regardless of the surface gradient, the ankle was consistently the dominant source of lower-limb positive mechanical power (47-55%). In the context of our results, we outline three distinct use-modes that could be emphasized in future lower-limb exoskeleton designs 1) Energy injection: adding positive work into the gait cycle, 2) Energy extraction: removing negative work from the gait cycle, and 3) Energy transfer: extracting energy in one gait phase and then injecting it in another phase (i.e., regenerative braking).

In the study of balance and postural control the (Single) Inverted Pendulum model (SIP) has been taken for a long time as an acceptable paradigm, with the implicit assumption that only ankle rotations are relevant for describing and explaining sway movements. However, more recent kinematic analysis of quiet standing revealed that hip motion cannot be neglected at all and that ankle-hip oscillatory patterns are characterized by complex in-phase and anti-phase interactions, suggesting that the SIP model should be substituted by a DIP (Double Inverted Pendulum) model. It was also suggested that DIP control could be characterized as a kind of optimal bi-axial active controller whose goal is minimizing the acceleration of the global CoM (Center of Mass). We propose here an alternative where active feedback control is applied in an intermittent manner only to the ankle joint, whereas the hip joint is stabilized by a passive stiffness mechanism. The active control impulses are delivered to the ankle joint as a function of the delayed state vector (tilt rotation angle + tilt rotational speed) of a Virtual Inverted Pendulum (VIP), namely a pendulum that links the ankle to the CoM, embedded in the real DIP. Simulations of such DIP/VIP model, with the hybrid control mechanism, show that it can reproduce the in-phase/anti-phase interaction patterns of the two joints described by several experimental studies. Moreover, the simulations demonstrate that the DIP/VIP model can also reproduce the measured minimization of the CoM acceleration, as an indirect biomechanical consequence of the dynamic interaction between the active control of the ankle joint and the passive control of the hip joint. We suggest that although the SIP model is literally false, because it ignores the ankle-hip coordination, it is functionally correct and practically acceptable for experimental studies that focus on the postural oscillations of the CoM.

Lower-limb exoskeletons have the potential to transform the way we move 1 – 14 , but current state-of-the-art controllers cannot accommodate the rich set of possible human behaviours that range from cyclic and predictable to transitory and unstructured. We introduce a task-agnostic controller that assists the user on the basis of instantaneous estimates of lower-limb biological joint moments from a deep neural network. By estimating both hip and knee moments in-the-loop, our approach provided multi-joint, coordinated assistance through our autonomous, clothing-integrated exoskeleton. When deployed during 28 activities, spanning cyclic locomotion to unstructured tasks (for example, passive meandering and high-speed lateral cutting), the network accurately estimated hip and knee moments with an average R 2 of 0.83 relative to ground truth. Further, our approach significantly outperformed a best-case task classifier-based method constructed from splines and impedance parameters. When tested on ten activities (including level walking, running, lifting a 25 lb (roughly 11 kg) weight and lunging), our controller significantly reduced user energetics (metabolic cost or lower-limb biological joint work depending on the task) relative to the zero torque condition, ranging from 5.3 to 19.7%, without any manual controller modifications among activities. Thus, this task-agnostic controller can enable exoskeletons to aid users across a broad spectrum of human activities, a necessity for real-world viability. A task-agnostic controller assists the user on the basis of instantaneous estimates of lower-limb biological joint moments from a deep neural network so exoskeletons can aid users across a broad spectrum of human activities.

The invention of the surgical robot enabled accurate component implantation during total hip arthroplasty (THA). However, a preoperative surgical planning methodology is still lacking to determine the acetabular cup alignment considering the patient-specific hip functions during daily activities such as walking. To simultaneously avoid implant edgeloading and impingement, this study established a kinematic–kinetic compliant (KKC) acetabular cup positioning method based on preoperative gait kinematics measurement and musculoskeletal modeling. Computed tomography images around the hip joint and their biomechanical data during gait, including motion tracking and foot–ground reaction forces, were collected. Using the reconstructed pelvic and femur geometries, the patient-specific hip muscle insertions were located in the lower limb musculoskeletal model via point cloud registration. The designed cup orientation has to be within the patient-specific safe zone to prevent implant impingement, and the optimized value selected based on the time-dependent hip joint reaction force to minimize the risk of edgeloading. As a validation of the proposed musculoskeletal model, the predicted lower limb muscle activations for seven patients were correlated with their surface electromyographic measurements, and the computed hip contact force was also in quantitative agreement with data from the literature. However, the designed cup orientations were not always within the well-known Lewinnek safe zone, highlighting the importance of KKC surgical planning based on patient-specific biomechanical evaluations.

Inertial sensor systems are becoming increasingly popular for gait analysis because their use is simple and time efficient. This study aimed to compare joint kinematics measured by the inertial sensor system RehaGait® with those of an optoelectronic system (Vicon®) for treadmill walking and running. Additionally, the test re-test repeatability of kinematic waveforms and discrete parameters for the RehaGait® was investigated. Twenty healthy runners participated in this study. Inertial sensors and reflective markers (PlugIn Gait) were attached according to respective guidelines. The two systems were started manually at the same time. Twenty consecutive strides for walking and running were recorded and each software calculated sagittal plane ankle, knee and hip kinematics. Measurements were repeated after 20min. Ensemble means were analyzed calculating coefficients of multiple correlation for waveforms and root mean square errors (RMSE) for waveforms and discrete parameters. After correcting the offset between waveforms, the two systems/models showed good agreement with coefficients of multiple correlation above 0.950 for walking and running. RMSE of the waveforms were below 5° for walking and below 8° for running. RMSE for ranges of motion were between 4° and 9° for walking and running. Repeatability analysis of waveforms showed very good to excellent coefficients of multiple correlation (>0.937) and RMSE of 3° for walking and 3–7° for running. These results indicate that in healthy subjects sagittal plane joint kinematics measured with the RehaGait® are comparable to those using a Vicon® system/model and that the measured kinematics have a good repeatability, especially for walking.

Analyses of joint moments are important in the study of human motion, and are crucial for our understanding of e.g. how and why ACL injuries occur. Such analyses may be affected by artifacts due to inconsistencies in the equations of motion when force and movement data are filtered with different cut-off frequencies. The purpose of this study was to quantify the effect of these artifacts, and compare joint moments calculated with the same or different cut-off frequency for the filtering of force and movement data. 123 elite handball players performed sidestep cutting while the movement was recorded by eight 240Hz cameras and the ground reaction forces were recorded by a 960Hz force plate. Knee and hip joint moments were calculated through inverse dynamics, with four different combinations of cut-off frequencies for signal filtering: movement 10Hz, force 10Hz, (10–10); movement 15Hz, force 15Hz; movement 10Hz, force 50Hz (10–50); movement 15Hz, force 50Hz. The results revealed significant differences, especially between conditions with different filtering of force and movement. Mean (SD) peak knee abduction moment for the 10–10 and 10–50 condition were 1.27 (0.53) and 1.64 (0.68) Nm/kg, respectively. Ranking of players based on knee abduction moments were affected by filtering condition. Out of 20 players with peak knee abduction moment higher than mean+1SD with the 10–50 condition, only 11 were still above mean+1SD when the 10–10 condition was applied. Hip moments were very sensitive to filtering cut-off. Mean (SD) peak hip flexion moment was 3.64 (0.75) and 5.92 (1.80) under the 10–10 and 10–50 conditions, respectively. Based on these findings, force and movement data should be processed with the same filter. Conclusions from previous inverse dynamics studies, where this was not the case, should be treated with caution.

Background We have shown that a prototype marathon racing shoe reduced the metabolic cost of running for all 18 participants in our sample by an average of 4%, compared to two well-established racing shoes. Gross measures of biomechanics showed minor differences and could not explain the metabolic savings. Objective To explain the metabolic savings by comparing the mechanics of the shoes, leg, and foot joints during the stance phase of running. Methods Ten male competitive runners, who habitually rearfoot strike ran three 5-min trials in prototype shoes (NP) and two established marathon shoes, the Nike Zoom Streak 6 (NS) and the adidas adizero Adios BOOST 2 (AB), at 16 km/h. We measured ground reaction forces and 3D kinematics of the lower limbs. Results Hip and knee joint mechanics were similar between the shoes, but peak ankle extensor moment was smaller in NP versus AB shoes. Negative and positive work rates at the ankle were lower in NP shoes versus the other shoes. Dorsiflexion and negative work at the metatarsophalangeal (MTP) joint were reduced in the NP shoes versus the other shoes. Substantial mechanical energy was stored/returned in compressing the NP midsole foam, but not in bending the carbon-fiber plate. Conclusion The metabolic savings of the NP shoes appear to be due to: (1) superior energy storage in the midsole foam, (2) the clever lever effects of the carbon-fiber plate on the ankle joint mechanics, and (3) the stiffening effects of the plate on the MTP joint.

Three-dimensional gait analysis has been used extensively in research. During walking, the external hip adduction moment (EHAM) has been used as a surrogate measure of joint loading in individuals with hip osteoarthritis and inconsistency between previous studies could be attributed to the inconsistency of static standing trials. The present study was designed to examine the effects of static trial foot position on hip and ankle kinetics and kinematics variables during walking. Twelve participants were recruited and completed three static trials: 20° toe-out, straight (0°), and 20° toe-in. Five walking trials (own pace and shoes) were collected. The dynamic trials were analysed using three static trials. The first-peak, trough, and second-peak EHAMs and other hip and ankle kinematics and kinetics were compared between the conditions using repeated-measures analysis of variance. The first peak, trough, and second peak EHAMs showed a significant increase during movement from 20° toe-in to 20° toe-out by 5.87 %, 7.74 %, and 7.68 %, respectively. Furthermore, significant changes were found in hip flexion angle, hip sagittal plane range of motion angle, hip adduction and abduction angles, hip internal and external rotation angles, hip internal rotation moment, ankle dorsiflexion and plantarflexion moments, and ankle inversion and eversion moments. In this study, the change in foot position during the within-subject trials affected the first peak, trough, and second peak EHAMs and other kinetic and kinematic variables during walking. Therefore, this study highlights the importance to standardise the foot position in static trials to avoid masking or accentuating the actual changes.

In a simple model of bipedal walking, both a muscle moment at the hip and an impulsive push generated through ankle plantarflexion power gait. There is a biomechanical tradeoff between ankle and hip moments in the sagittal plane. Although ankle pushoff is primarily sagittal, its impact on frontal-plane mechanics, which are related to hip and knee injury risk, remains underexplored. This study aimed to investigate how increased ankle pushoff influences frontal-plane hip and knee moments during level walking. Understanding these effects could guide treatments for individuals with hip or knee symptoms linked to frontal-plane mechanics. Thirty-seven healthy adults walked on an instrumented treadmill under two conditions: Habitual (typical gait) and Push (increased ankle pushoff). Kinematic and kinetic data were collected and normalized for gait cycle and body weight. Statistical parametric mapping and peak value analysis were used to compare differences in internal joint moments and angles between conditions. Increased pushoff was confirmed by greater ankle plantarflexion moments and angular impulse in the Push condition. At the hip, increased pushoff resulted in a greater abduction moment early in stance and a reduced abduction moment and adduction angle late in stance. At the knee, increased pushoff led to a greater abduction moment late in stance. These findings suggest that increasing ankle pushoff during walking has significant effects on hip and knee frontal-plane biomechanics, which may not be beneficial for individuals with conditions influenced by hip and knee abduction moments.