Gait Strategies Research Articles

Application of control strategies and machine learning techniques in prosthetic knee: a systematic review

This systematic review focuses on control strategies and machine learning techniques used in prosthetic knees for restoring mobility of individuals with trans-femoral amputations. Review and classification of control strategies that determine how these prosthetic knees interact with the user and gait strategy inspired algorithms for phase identification, locomotion mode, and motion intention recognition were studied. Relevant studies were identified using electronic databases such as PubMed, EMBASE, SCOPUS, and the Cochrane Controlled Trials Register (Rehabilitation and Related Therapies) up to April 2021. Abstracts were screened and inclusion and exclusion criteria were applied. Out of 278 potentially relevant studies, 65 articles were included. The specific variables on control approach, control modes, gait control, hardware level, machine learning algorithm, and measured signals mechanism were extracted and added to summary table. The results indicate that advanced methods for adapting position or torque depiction and automatic detection of terrains or gait modes are more commonly utilized, but they are largely limited to laboratory environments. It is concluded that a correct combination of control strategies and machine learning techniques will enable the improvement of prosthetic performance and enhance the standard of amputee’s lives.

Emergence of the London Millennium Bridge instability without synchronisation

The pedestrian-induced instability of the London Millennium Bridge is a widely used example of Kuramoto synchronisation. Yet, reviewing observational, experimental, and modelling evidence, we argue that increased coherence of pedestrians’ foot placement is a consequence of, not a cause of the instability. Instead, uncorrelated pedestrians produce positive feedback, through negative damping on average, that can initiate significant lateral bridge vibration over a wide range of natural frequencies. We present a simple general formula that quantifies this effect, and illustrate it through simulation of three mathematical models, including one with strong propensity for synchronisation. Despite subtle effects of gait strategies in determining precise instability thresholds, our results show that average negative damping is always the trigger. More broadly, we describe an alternative to Kuramoto theory for emergence of coherent oscillations in nature; collective contributions from incoherent agents need not cancel, but can provide positive feedback on average, leading to global limit-cycle motion.

청소년 비만정도와 보행 지면반력의 관계 연구

Overweight or obese adolescents are at a high risk of injury due to the load applied to their body joints while walking. Therefore, the purpose of this study was to define a difference in GRF(Ground Reaction Force) according to the gait cycle of normal, overweight, and obese groups in adolescence, and to identify the gait characteristics of overweight(obese) adolescents.<BR> Healthy adolescents were recruited and classified into normal, overweight, and obesity according to the degree of obesity(BMI). In addition, events were set as E1(LR: Loading Response), E2(MSLS: Mid Single Limb Stance), and E3(PS: Pre-Swing). For each event, the GRF of both feet was calculated along x(ML: MedioLateral), y(AP: AnteroPosterior), and z(Vertical) axes. The calculated GRF was normalized to the weight of each subject, so %BW was computed. Mean and standard deviation were calculated, multivariate analysis of variance(MANOVA) and Correlation analysis(Pearson, both side) were practiced. The statistical significance level was set to .05.<BR> Vertical GRF of LR in left foot from normal group was greater than obese group, and left and right feet ML GRF of MSLS from both overweight and obese groups showed smaller than normal group(p＜.05). Overweight and obese groups had greater right feet ML GRF of PS than normal group, and overweight group showed higher values than normal group in left foot Vertical GRF of PS, too(p＜.05). In addition, in PS of normal group, BMI and AP GRF in both feet of showed a negative correlation, and in MSLS of obese group, AP GRF in left foot showed a negative correlation(p＜.05).<BR> In the gait of overweight and obese group, they have a gait characteristic that reducing Vertical GRF to decrease the amount of impulse from the load response. Since this gait strategy may cause more joint fatigue, intervention to correct a gait posture along with reduction of body fat will be demended.

Dynamic stability during gait in idiopathic normal pressure hydrocephalus and Parkinson's disease.

To clarify a characteristic of dynamic stability during gait in idiopathic normal pressure hydrocephalus (iNPH) and Parkinson's disease (PD), and to explore the association between dynamic stability and disease severity in each disease. The 5-m gait of 36 iNPH (precerebrospinal fluid drainage), 20 PD (medicated state), and 25 healthy controls (HC) were evaluated using three-dimensional motion analysis. Ambulatory dynamic stability was defined as the ability to maintain the extrapolated center of mass within the base of support at heel contact, with the distance between the two referred to as the margin of stability (MOS). Anteroposterior direction (AP) MOS was significantly larger in the iNPH and PD groups than in the HC group; no significant difference was found between the iNPH and PD groups. Mediolateral direction (ML) MOS was significantly larger in the iNPH and PD groups than in the HC group and significantly larger in the iNPH group than in the PD group. In the iNPH group, the disease severity was positively correlated with only ML MOS. In the PD group, the disease severity was positively correlated with the AP MOS and ML MOS. Dynamic stability in iNPH increases in AP and ML, and it may be associated with not only iNPH-associated gait disturbance but also with a voluntarily cautious gait strategy. Dynamic stability in PD only increased in AP, and this may be associated with PD symptoms. These findings will help physicians understand the difference in pathological gait including dynamic stability between patients with iNPH and PD.

Longitudinal changes in energy cost during walking in boys with Duchenne Muscular Dystrophy (DMD).

In boys with DMD, muscle weakness progresses in a proximal to distal pattern, leading to compensatory gait strategies, including hyperlordosis and equinus, that increase energy cost and accelerate the loss of walking capacity. The purpose of this study was to determine the changes in the energy cost of walking that occur with disease progression and to determine the optimal normalization scheme for the longitudinal assessment of the energy cost of walking in boys with DMD. Energy cost was assessed with the COSMED K4b2. Three normalization schemes were examined: gross energy cost (EC), net non-dimensional oxygen cost (NNcost) and speed-matched control energy cost (SMC-EC). Nonlinear mixed modeling procedures determined the rate of change with age. Linear regression was used to asses the relationship between each normalization scheme and age and body height. 74 boys with DMD were assessed for the energy cost of walking. Velocity decreased at a significant rate (-.00245/month, p = .03) across time; (Fig. 2), while gross EC (.003248/month, p = 0.0026), NNcost (.006155/month, p < 0.0001) and SMC-EC (.001690/month, p = 0.03) all increased significantly. Age and height were significantly associated with NNcost and SMC-EC. The sensitivity of NNcost and SMC-EC to age over time were similar, while SMC-EC was less sensitive to changes in height over time than NNcost. In contrast to able-bodied peers, boys with DMD decrease their velocity while all walking energy cost measures increased over time. Both SMC-EC and NNcost proved appropriate normalization schemes for boys with DMD. Compared to gross EC, both NNcost and SMC-EC were less sensitive to changes in age over time, while SMC-EC was less sensitive to changes in height than NNcost. Therefore, both NNCost and SMC-EC are suggested normalization schemes for the longitudinal assessment of energy cost in boys with DMD.

Leg and Joint Stiffness Adaptations to Minimalist and Maximalist Running Shoes.

The running footwear literature reports a conceptual disconnect between shoe cushioning and external impact loading: footwear or surfaces with greater cushioning tend to result in greater impact force characteristics during running. Increased impact loading with maximalist footwear may reflect an altered lower-extremity gait strategy to adjust for running in compliant footwear. The authors hypothesized that ankle and knee joint stiffness would change to maintain the effective vertical stiffness, as cushioning changed with minimalist, traditional, and maximalist footwear. Eleven participants ran on an instrumental treadmill (3.5m·s-1) for a 5-minute familiarization in each footwear, plus an additional 110 seconds before data collection. Vertical, leg, ankle, and knee joint stiffness and vertical impact force characteristics were calculated. Mixed model with repeated measures tested differences between footwear conditions. Compared with traditional and maximalist, the minimalist shoes were associated with greater average instantaneous and average vertical loading rates (P < .050), greater vertical stiffness (P ≤ .010), and less change in leg length between initial contact and peak resultant ground reaction force (P < .050). No other differences in stiffness or impact variables were observed. The shoe cushioning paradox did not hold in this study due to a similar musculoskeletal strategy for running in traditional and maximalist footwear and running with a more rigid limb in minimalist footwear.

Anticipatory and reactive responses to underfoot perturbations during gait in healthy adults and individuals with a recent mild traumatic brain injury

BackgroundFollowing mild traumatic brain injury, individuals often exhibit quantifiable gait deficits over flat surfaces, but little is known about how they control gait over complex surfaces. Such complex surfaces require precise neuromotor control to anticipate and react to small disturbances in walking surfaces, and mild traumatic brain injury-related balance deficits may adversely affect these gait adjustments. MethodsThis study investigates anticipatory and reactive gait adjustments for expected and unexpected underfoot perturbations in healthy adults (n = 5) and individuals with mild traumatic brain injury (n = 5). Participants completed walking trials with random unexpected or expected underfoot perturbations from a mechanized shoe and inertial measurement units collected kinematic data from the feet and sternum. Linear mixed-effects models assessed the effects of segment, group, and their interaction on standardized difference of accelerations between perturbation and non-perturbation trials. FindingsBoth groups demonstrated similar gait strategies when perturbations were unexpected. During late swing phase before expected perturbations, persons with mild traumatic brain injury exhibited greater lateral acceleration of their perturbed foot and less lateral movement of their trunk compared with unperturbed gait. Control participants exhibited less lateral foot acceleration and no difference in mediolateral trunk acceleration compared with unperturbed gait during the same period. A significant group*segment interaction (p < 0.001) during this part of the gait cycle suggests the groups adopted different anticipatory strategies for the perturbation. InterpretationIndividuals with mild traumatic brain injury may be adopting cautious strategies for expected perturbations due to persistent neuromechanical deficits stemming from their injury.

Trunk lean and toe out gait strategies impact on lower limb joints

Gait retraining as a non-invasive prospective approach to restore mechanical loading at the knee joint and slowing down knee osteoarthritis (OA) progression shows great promise. However, the impact of gait modifications such as an increase in foot progression angle (FPA) or lateral trunk lean (LTL) on the ankle and hip is not yet well understood. Thus, the goal of this study is to provide insight on the impact of FPA and LTL on the sagittal and frontal external moments at the ankle and hip of healthy participants. We hypothesize that there is an optimum, for which an increase in FPA and/or LTL minimize the knee adduction moment (KAM) without increasing significantly the frontal and sagittal external moments at the ankle and hip during gait. To test this hypothesis, 23 participants performed walking trials with modified FPA and/or LTL angles following a real-time visual feedback. The hypothesis was not confirmed and while not all the gait modifications performed by the participants in this study reduced the KAM, they significantly increased the sagittal moment at the ankle and the frontal moment at the hip. This study highlights the importance to consider the biomechanical consequences of gait modifications on the ankle and hip before considering a clinical application of gait retraining approaches.

Relationships between cognitive factors and gait strategy during exoskeleton-augmented walking

Individual variation in exoskeleton-augmented gait strategy may arise from differences in cognitive factors, e.g., ability to respond quickly to stimuli or complete tasks under divided attention. Gait strategy is defined as different approaches to achieving gait priorities (e.g., walking without falling) and is observed via changes in gait characteristics like normalized stride length or width. Changes indicate shifting priorities like increasing stability or coordination with an exoskeleton. Relationships between cognitive factors and exoskeleton gait characteristics were assessed. Cognitive factors were quantified using a modified Simon task and a speed achievement task on a self-paced treadmill with and without a secondary go/no-go task. Individuals with faster reaction times and decreased ability to maintain a given speed tended to prioritize coordination with an exoskeleton over gait stability. These correlations indicate relationships between cognitive factors and individual exoskeleton-augmented gait strategy that should be further investigated to understand variation in exoskeleton use.

Metrics for quantifying cognitive factors that may underlie individual variation in exoskeleton use

Individual differences in adaptation to exoskeletons have been observed, but are not well understood. Kinematic, kinetic, and physiologic factors are commonly used to assess these systems. Parameters from experimental psychology and gait literature wereadapted to probe the lower extremity perception-cognition-action loop using measures of reaction times, gait task performance, and gait strategy. Parameters were measured in 15 subjects via two tasks: (1) a modified Simon task and (2) a speed-achievement task with secondary go/no-go cues on a self-paced treadmill. Outcome metrics were assessed for significantly different intra- versus inter-subject variability. Reaction time measures from the modified Simon task, as well two speed-achievement metrics and one gait-strategy characteristic we re found to show significant differenc es in intra- versus inter-subject variability. These results suggest that select cognitive factors may differentiate between individuals and be potential predictors for individual variation during exoskeleton system operation.

Gait characteristics during crossing over obstacle in patients with glaucoma using insole foot pressure.

Background:Glaucoma, is the most common cause of irreversible visual deficits, presents as an injury to the optic nerve and it is mainly associated with elevated intraocular pressure. The main symptom of glaucoma is a reduction of the visual field, which is usually a source of complaint at the advanced stage of disease. Because of visual deficit, gait dysfunctions, including low gait speed and increased bumping into objects, postural sway, and falling are occurred. Many studies have used stopwatch or motion-sensing devices to report on gait function following glaucoma. However, there are few reports on gait dysfunction assessed by examining foot pressure. This study investigated gait ability following glaucoma according to different gait conditions by assessing foot pressure.Methods:Thirty older adults (15 in the sex- and age-matched normal group and 15 in the glaucoma group) were recruited for this study. All participants were walked under 2 different gait conditions in an F-scan system and the subject’ assessments were randomly assigned to rule out the order effect. Conditions included: gait over an obstacle in a straight 6 m path, gait in a straight path without an obstacle in the 6 m path. Gait variables included cadence, gait cycle, stance time, center of force (COF) deviation, and COF excursion. About 10 minutes were taken for gait evaluation.Results:When walking without an obstacle on a 6 m path, there were significant differences between the 2 groups in gait speed, cadence, gait cycle, and stance time (P < .05). There were significant differences when walking with an obstacle on a 6 m path (P < .05). Two-way analysis of variance showed significant effects associated with “glaucoma” not gait condition on all outcomes except for COF deviation and excursion. Also, there was no the interaction effect between “glaucoma” and “gait condition.”Conclusion:We demonstrated that glaucoma patients selected the gait strategy such as lower gait function in both gait conditions particularly, slower gait speed and cadence and longer gait cycle and stance time, as determined by examining foot pressure. We believe that our results could help to improve the quality of life of patients with glaucoma.

Evaluating the energetics of entrainment in a human\u2013machine coupled oscillator system

During locomotion, humans sometimes entrain (i.e. synchronize) their steps to external oscillations: e.g. swaying bridges, tandem walking, bouncy harnesses, vibrating treadmills, exoskeletons. Previous studies have discussed the role of nonlinear oscillators (e.g. central pattern generators) in facilitating entrainment. However, the energetics of such interactions are unknown. Given substantial evidence that humans prioritize economy during locomotion, we tested whether reduced metabolic expenditure is associated with human entrainment to vertical force oscillations, where frequency and amplitude were prescribed via a custom mechatronics system during walking. Although metabolic cost was not significantly reduced during entrainment, individuals expended less energy when the oscillation forces did net positive work on the body and roughly selected phase relationships that maximize positive work. It is possible that individuals use mechanical cues to infer energy cost and inform effective gait strategies. If so, an accurate prediction may rely on the relative stability of interactions with the environment. Our results suggest that entrainment occurs over a wide range of oscillation parameters, though not as a direct priority for minimizing metabolic cost. Instead, entrainment may act to stabilize interactions with the environment, thus increasing predictability for the effective implementation of internal models that guide energy minimization.

The role of load-dependent sensory input in the control of balance during gait in rats.

Locomotor activity requires fine balance control that strongly depends on the afferent input from the load receptors. Following hindlimb unloading (HU), the kinematic and EMG activity of the hindlimbs is known to change significantly. However, the effects of HU on the integrative control mechanisms of posture and locomotion are not clear. The goal of the present study was to evaluate the center of mass (CoM) dynamic stabilization and associated adaptive changes in the trunk and hindlimb muscle activity during locomotion after 7 days of HU. The EMG signals from the muscles of the low lumbar trunk [m. longissimus dorsi (VERT)] and the hind limb [m. tibialis anterior (TA), m. semitendinosus (ST), m. soleus (SOL)] were recorded together with the hindquarter kinematics during locomotion on a treadmill in six rats before and after HU. The CoM lateral shift in the step cycle significantly increased after HU and coincided with the enhanced activity of the VERT. The mean EMG of the TA and the ST flexor activity increased significantly with reduction of their burst duration. These data demonstrate the disturbances of body balance after HU that can influence the basic parameters of locomotor activity. The load-dependent mechanisms resulted in compensatory adjustments of flexor activity toward a faster gait strategy, such as a trot or gallop, which presumably have supraspinal origin. The neuronal underpinnings of these integrative posture and locomotion mechanisms and their possible reorganization after HU are discussed.

Usual and dual-task gait adaptations under visual stimulation in older adults at different ages.

During the walk along the streets, older adults are exposed to various visual stimuli that can affect their gait in a harmful or beneficial way. To evaluate gait strategies during different situations with and without visual stimulation in older adults to identify the influence of the visual stimulus on these gait parameters. A total of 200 older adults were divided into 4 groups according to age range between 60 and 102years. Gait was evaluated in the following situations: (1) habitual gait (HG); (2) gait with the visual stimulation (GVS) provided by a pedestrian traffic light, and (3) GVS associated with a cognitive task (GVS-C). The GAITRite Platinum equipment was used to assess gait variables. Comparison of GVS and HG revealed that the visual stimulus influences the gait parameters and promotes a gait speed increase. However, to increase their gait speed, older adults aged 60-89years used strategies of increased step length and cadence, whereas subjects older than 90years used only strategies of increased cadence. In addition, comparison of GVS and GVS-C revealed a decrease in gait speed in all age ranges when the cognitive task was added, although this reduction was more pronounced in subjects older than 70years. Visual stimulus influences the gait parameters in older adults and the strategy used is different depending on their age, a fact that shows that traffic light may be an interesting strategy to improve the gait performance during physical therapy.

Effect of Heel-First Strike Gait on Knee and Ankle Mechanics.

Background and Objectives: Acquiring knowledge about the magnitude and direction of induced joint forces during modifying gait strategies is critical for proper exercise prescription. The present study aimed to evaluate whether a heel-first strike pattern during gait can affect the biomechanical characteristics of ankle and knee joints among asymptomatic people. Materials and Methods: In this cross-sectional study performed in the biomechanics laboratory, 13 professional healthy male athletes walked on an instrumented walkway under two walking conditions. For the normal condition, subjects were instructed to walk as they normally would. For the heel-first strike condition, subjects were instructed to walk with heel-first strike pattern and increase heel contact duration as much as possible. Then, knee and ankle joint range of motions and moments, as well as vertical ground reaction force was measured by the Kistler force plate and Vicon motion analysis system. Results: Knee flexion angle at the initial contact and during stance phase was significantly lower when increasing the heel strike pattern. In addition, the mean values of the knee external rotation and adductor moments during heel strike condition were lower than those in normal walking. Further, the ankle dorsiflexion range of motion (ROM) during mid-stance increased significantly during heel-first strike pattern compared to the value in normal gait pattern. Conclusions: The modification of gait pattern including heel-first strike pattern can reduce the mechanical load applied to the knee, while improving the extensibility of gastro-soleus muscle complex.

Gait Adaptations at 8 Years After Reconstruction of Unilateral Isolated and Combined Posterior Cruciate Ligament Injuries

Background: It remains unclear how posterior cruciate ligament (PCL) reconstruction influences long-term lower extremity joint biomechanics. Purpose: To determine whether patients who underwent PCL reconstruction exhibited long-term alterations in lower limb gait mechanics. Study Design: Controlled laboratory study. Methods: A total of 26 patients underwent gait analyses at 8.2 ± 2.6 years after primary unilateral PCL reconstruction. Sex- and age-matched healthy controls were analyzed for comparison. Gait data were collected using motion capture and force plates. Hip, knee, and ankle angles and moments were compared during initial contact, early stance, and late stance for the reconstructed and uninjured contralateral limbs of patients who underwent PCL reconstruction (PCL group) as well as the limbs of healthy control participants (CON group). Results: No side-to-side kinematic differences were noted between the reconstructed and contralateral limbs of the PCL group; some trivial differences were noted in knee and hip moments. However, major differences between the PCL and CON groups occurred at the knee. Reconstructed and contralateral limbs of the PCL group exhibited larger knee flexion angles during initial contact (Δ = 7.0° [P < .001] and Δ = 6.9° [P < .001], respectively), early stance (Δ = 5.8° [P = .003] and Δ = 6.7° [P < .001], respectively), and late stance (Δ = 7.9° [P < .001] and Δ = 8.0° [P < .001], respectively) compared with the CON group. During early stance, contralateral limbs of the PCL group displayed larger knee flexion moments (Δ = 0.20 N·m/kg; P = .014) compared with the CON group, and both reconstructed (Δ = 0.05 N·m/kg; P = .027) and contralateral (Δ = 0.07 N·m/kg; P = .001) limbs of the PCL group exhibited larger knee external rotation moments compared with the CON group. During late stance, reconstructed and contralateral limbs of the PCL group exhibited smaller knee extension moments (Δ = 0.24 N·m/kg [P < .001] and Δ = 0.26 N·m/kg [P < .001], respectively) and knee internal rotation moments (Δ = 0.06 N·m/kg [P < .001] and Δ = 0.06 N·m/kg [P < .001], respectively) compared with the CON group. No discrepancies were observed at the hip; minimal differences were noted in sagittal-plane ankle mechanics. Conclusion: Patients who underwent PCL reconstruction generally exhibited bilateral gait symmetry at 8 years after surgery. However, they exhibited important biomechanical deviations in both knees compared with healthy controls. These modifications likely reflect adaptive gait strategies to protect the PCL after reconstruction. Clinical Relevance: Long-term follow-up analyses of patients who underwent PCL reconstruction should not use the uninjured contralateral limb as a “healthy” reference, as it also exhibits mechanical differences compared with controls. Results could inform the development of neuromuscular and strength training programs targeting the restoration of knee biomechanics similar to healthy controls to prevent early-onset degeneration that is frequently associated with altered biomechanics.

Anterior knee pain from the evolutionary perspective

BackgroundThis paper describes the evolutionary changes in morphology and orientation of the PFJ using species present through our ancestry over 340 million years. Methods37 specimens from the Devonian period to modern day were scanned using a 64-slice CT scanner. 3D geometries were created following routine segmentation and anatomical measurements taken from standardised bony landmarks. ResultsFindings are described according to gait strategy and age. The adoption of an upright bi-pedal stance caused a dramatic change in the loading of the PFJ which has subsequently led to changes in the arrangement of the PFJ. From Devonian to Miocene periods, our sprawling and climbing ancestors possessed a broad knee with a shallow, centrally located trochlea. A more rounded knee was present from the Paleolithic period onwards in erect and bipedal gait types (aspect ratio 0.93 vs 1.2 in late Devonian), with the PFJ being placed lateral to the midline compared to the medial position in quadrapeds. The depth of the trochlea groove was maximal in the Miocene period of the African ground apes with associated acute sulcus angles in Gorilla (117°) becoming more flattened towards the modern human (138°). ConclusionsThe evolving bipedal gait lead to anteriorisation of the patellofemoral joint, flattening of the trochlea sulcus, in a more lateral, dislocation prone arrangement. Ancestral developments might help explain the variety of presentations of anterior knee pain and patellofemoral instability.

Effect of medial foot loading self-practice on lower limb kinematics in young individuals with asymptomatic varus knee alignment

BackgroundVarus alignment of the knee is a risk factor for developing knee osteoarthritis. Recently, voluntary shifting the plantar pressure distribution medially (medial foot loading) during gait has been found to reduce knee adduction angle during stance, which may lower the joint load. However, it is not yet known whether such effect would persist after long-term self-practice. This study aimed to determine whether medial foot loading can be an effective self-care protocol for reducing the knee adduction angle. MethodsEight subjects with asymptomatic varus knee alignment were trained on medial foot loading once in a laboratory, then carried out as self-practice for 8 weeks outside the laboratory. Spatiotemporal gait parameters and lower limb joint kinematics data were collected during natural walking prior to the training (baseline walking), during the practice session immediately after the initial training (trained walking), and during natural walking after the self-practice period (post-practice walking). ResultsParticipants walked significantly faster after the self-practice period with longer step length compared with the baseline. The knee adduction angle at initial contact, maximum angle during stance, and mean angle during a gait cycle were significantly decreased during both the trained and post-practice walking compared with baseline. The 8-week self-practice caused larger decrements in the three angles than the single training, but no significant differences were found between the two conditions. ConclusionsSelf-practice of medial foot loading walking could be an effective gait strategy to reduce the knee adduction angle. The effect could be sustained for individuals with asymptomatic varus knee alignment.

Reconfigurable Curved Beams for Selectable Swimming Gaits in an Underwater Robot

Rowing is a swimming motion employed by a number of animals via tuned passive biomechanics and active gait strategies. This gait generates positive net thrust (or moment) by having a higher drag profile in the power stroke compared with the recovery stroke, which is obtained via faster actuation speed or higher effective area. In this letter, we show that using the preferential buckling of curved beams in swimming robots can, via a passive reduction of effective area in recovery stroke, be used to generate positive net thrust and moment. Additionally, these curved beams can be actively tuned to alter their behavior on demand for use in swimming applications, and can be used in an underwater robot to switch between rowing and flapping gaits. A dynamic model has been developed to model the swimming behavior of a robot using buckling joints. A design optimization has been carried out, using the Covariance Matrix Adaption Evolution Strategy (CMA-ES), to find the design and gait parameters that maximize the robot's forward swimming speed. A series of experimental gait searches have subsequently been conducted on the resulting optimal design, again using CMA-ES with the goal of finding the optimal gait pattern across a number of swimming strategies such as paddling, flapping, and undulation. By actively altering the curved beam's buckling limits, an untethered robot has been developed that maneuvers in water across each of these swimming strategies. The findings suggest that tuning the preferential buckling limits of curved beams can be an effective and potentially advantageous approach for producing directional thrust and moments.

Lower Limb Biomechanical Responses During a Standardized Load Carriage Task are Sex Specific.

The purpose of this study was to investigate sex-specific lower limb biomechanical adaptations during a standardized load carriage task in response to a targeted physical training program. Twenty-five healthy civilians (males [n = 13] and females [n = 12]) completed a load carriage task (5 km at 5.5 km·h-1, wearing a 23 kg vest) before and after a 10-week lower-body-focused training program. Kinematics and ground reaction force data were collected during the task and were used to estimate lower limb joint kinematics and kinetics (i.e., moments and powers). Direct statistical comparisons were not conducted due to different data collection protocols between sexes. A two-way repeated measures ANOVA tested for significant interactions between, and main effects of training and distance marched for male and female data, respectively. Primary kinematic and kinetic changes were observed at the knee and ankle joints for males and at the hip and knee joints for females. Knee joint moments increased for both sexes over the 5 km distance marched (P > .05), with males demonstrating significant reductions in peak knee joint extension after training. Hip adduction, internal rotation, and knee internal rotation angles significantly increased after the 5 km load carriage task for females but not males. Differences in adaptive gait strategies between sexes indicate that physical training needs to be tailored to sex-specific requirements to meet standardized load carriage task demands. The findings highlighted previously unfound sex-specific responses that could inform military training and facilitate the integration of female soldiers into physically demanding military roles.