Dynamic Joint Stiffness Research Articles

Associations amongst dynamic knee stiffness during gait, quadriceps stiffness, and the incidence of knee osteoarthritis over 24 months: a cohort study with a mediation analysis

BackgroundDecreased strength and increased stiffness of the quadriceps have been associated with a higher risk of developing knee osteoarthritis (OA) in elders. Dynamic joint stiffness (DJS) represents collective resistance from active and passive knee structures for dynamic knee motions. Elevated sagittal knee DJS has been associated with worsening of cartilage loss in knee OA patients. Altered quadriceps properties may affect DJS, which could be a mediator for associations between quadriceps properties and knee OA. Hence, this study aimed to examine whether DJS and quadriceps properties would be associated with the development of clinical knee OA over 24 months, and to explore the mediation role of DJS in associations between quadriceps properties and knee OA.MethodsThis was a prospective cohort study with 162 healthy community-dwelling elders. Gait analysis was conducted to compute DJS during the loading response phase. Quadriceps strength and stiffness were evaluated using a Cybex dynamometer and shear-wave ultrasound elastography, respectively. Knee OA was defined based on clinical criteria 24 months later. Logistic regression with generalized estimating equations was used to examine the association between quadriceps properties and DJS and incident knee OA. Mediation analysis was performed to explore the mediation role of DJS in associations between quadriceps properties and the incidence of knee OA.ResultsA total of 125 participants (65.6 ± 4.0 years, 58.4% females) completed the 24-month follow-up, with 36 out of 250 knees identified as clinical knee OA. Higher DJS (OR = 1.86, 95%CI: 1.33–2.62), lower quadriceps strength (1.85, 1.05–3.23), and greater quadriceps stiffness (1.56, 1.10–2.21) were significantly associated with a higher risk of clinical knee OA. Mediation analysis showed that the DJS was not a significant mediator for the associations between quadriceps properties and knee OA.ConclusionsHigher sagittal knee dynamic joint stiffness, lower quadriceps strength, and greater quadriceps stiffness are potential risk factors for developing clinical knee OA in asymptomatic elders. Associations between quadriceps properties and knee OA may not be mediated by dynamic joint stiffness. Interventions for reducing increased passive properties of the quadriceps and knee joint stiffness may be beneficial for maintaining healthy knees in the aging population.

Dynamic joint stiffness in individuals with femoroacetabular impingement syndrome pre- and post-hip arthroscopy

BackgroundPatients with hip-related pain often fail to return to their desired level of activity following hip arthroscopy. Lasting biomechanics alterations may be one potential explanation. Dynamic joint stiffness assesses the mechanistic controls of the lower limb during high impact movements, and thus, may provide valuable clinical targets to improving movement and optimizing return to activity after surgery. MethodsTwenty-five participants (13 females) with hip-related pain underwent 3D motion capture during a drop jump task before surgery and six months post-operatively. Nineteen healthy controls (9 females) were collected for comparison. Sagittal plane dynamic joint stiffness was calculated during the initial landing phase. Baseline and 6-month dynamic joint stiffness data were compared 1) between males and females with hip-related pain and 2) between individuals with hip-related pain and controls using Wilcoxon Signed-Rank and Mann Whitney U tests. Sexes were analyzed separately. FindingsFrom baseline to 6 months post-operatively, females with hip-related pain demonstrated decreased dynamic ankle stiffness (2.26 Nm/deg. [0.61] to 1.84 Nm/deg. [0.43]) (p = .005) and males with hip-related pain demonstrated increased dynamic hip stiffness (2.73 [0.90] to 3.88 [1.73]) (p = .013). There were no differences in dynamic stiffness at any joint between individuals with hip-related pain at either timepoint when compared to controls (p ≥ .099). InterpretationFemales and males with hip-related pain may demonstrate unique changes in dynamic joint stiffness after surgery, indicating return to activity may follow different trajectories for each sex. Additional work should examine the relationship between hip joint stiffness and treatment outcomes and identify additional movement-related rehabilitation targets.

Perceptions and biomechanical effects of varying prosthetic ankle stiffness during uphill walking: A case series

BackgroundProsthetic foot stiffness, which is typically invariable for commercially available prosthetic feet, needs to be considered when prescribing a prosthetic foot. While a biological foot adapts its function according to the movement task, an individual with lower limb amputation may be limited during more functionally demanding gait tasks by their conventional energy storing and return prosthetic foot. Research questionHow do changes in prosthetic foot stiffness during incline walking affect biomechanical measures as well as perception of participants. MethodsKinetic and kinematic data were collected during incline walking, for five participants with trans-tibial amputation. A mixed model analysis of variance was used to analyse the effects of changing the stiffness during incline walking, using a novel variable-stiffness unit built on a commercially available prosthetic foot. Biomechanical results were also analysed on an individual level alongside the participant feedback, for a better understanding of the various strategies and perceptions exhibited during incline walking. ResultsStatistically significant effects were only observed on the biomechanical parameters directly related to prosthetic ankle kinematics and kinetics (i.e., peak prosthetic ankle dorsiflexion, peak prosthetic ankle power, dynamic joint stiffness during controlled dorsiflexion). Participant perception during walking was affected by changes in stiffness. Individual analyses revealed varied perceptions and varied biomechanical responses among participants. SignificanceWhile changes in prosthesis mechanical properties influenced the amputee’s experience, minimal immediate effects were found with the overall gait pattern. The reported inter-participant variability may be due to the person’s physical characteristics or habitual gait pattern, which may influence prosthesis function. The ability to vary prosthetic foot stiffness during the assessment phase of setting up a prosthesis could provide useful information to guide selection of the appropriate prosthetic device for acceptable performance across a range of activities.

The interaction effect of different footwear types and static navicular drop or dynamic ankle pronation on the joint stiffness of the lower limb during running

BackgroundAlthough the effects of footwear type on joint stiffness have previously been investigated, researchers did not consider foot flexibility. Thus, the present investigation aimed to determine the interaction effects of footwear type, static navicular drop and dynamic ankle pronation on dynamic joint stiffness in running. Research questionDoes the footwear types in interaction with the foot posture affect the stiffness of the joints of the lower limb? MethodsForty-seven male individuals participated in this study. Firstly, they were divided into the high navicular, low navicular, and normal navicular drop. Secondly, they were divided into the high dynamic ankle pronation, low dynamic ankle pronation, and normal dynamic ankle pronation groups. Participants performed three running trials at 3 ± 0.2 m/s at minimalist footwear, conventional footwear, and barefoot conditions. We collected the ground reaction forces and three-dimensional kinematic data and calculated joint stiffness over the stance phase. ResultsThere was no significant main effect of navicular drop or dynamic ankle pronation on dynamic joint stiffness for the ankle, knee, and hip (p > 0.05). However, footwear type significantly affected dynamic joint stiffness. The pairwise comparison revealed that the ankle and hip dynamic joint stiffness magnitudes in the conventional footwear condition were greater than in the barefoot and minimalist footwear conditions (p 0.001). In contrast, the knee dynamic joint stiffness magnitude in the conventional footwear condition was lesser than in barefoot and minimalist footwear conditions (p 0.001). SignificanceThe navicular drop or dynamic ankle pronation did not influence lower limb joint stiffness, and there was no significant interaction between navicular drop or dynamic ankle pronation and footwear on lower limb dynamic joint stiffness. However, conventional footwear increased the ankle and hip dynamic joint stiffness while reducing knee dynamic joint stiffness, leading to changes in transfer energy, which could have implications for relative injury risk.

Sex differences in dynamic joint stiffness during walking in older adults

BackgroundKnee osteoarthritis (OA) often occurs in older women. Walking assistance such as knee brace is used to reduce mechanical stress on the knee, preventing OA onset. Dynamic joint stiffness (DJS) quantifies the resistance of an assistive device, providing a foundation for an objective bending stiffness prescription model. DJS may show sex differences among older adults. Research questionThis study aimed to investigate sex differences in lower limb DJS in the sagittal plane during walking in older adults. MethodsA total of 132 healthy older adults, aged 65 years or older (71 men and 61 women), were extracted from a public dataset. DJS of the hip, knee, and ankle joints in the sagittal plane was determined during the power absorption phase of the stance. DJS, joint angular excursion, and Δ joint moment were compared between older men and women using the Mann-Whitney U test. In addition, the r-value was calculated to represent the effect size of the differences in amplitude. ResultsAnkle DJS in older women was significantly lower with a reduced Δ ankle plantar flexion moment compared with that into men (p < 0.001 and p = 0.001; r = 0.35 and 0.42, respectively). Additionally, knee DJS was lower in older women (p = 0.007). However, since the joint angular excursion and ΔMoment showed no differences (p = 0.624 and 0.222, respectively), the effect size was small (r = 0.24). Hip DJS showed no significant sex differences (p = 0.703). SignificanceThese results suggest that the decrease in ankle DJS in older women was caused by the reduced ankle plantarflexion moment. Thus, support for ankle DJS is necessary for healthy older women. Nonetheless, knee DJS does not elucidate the cause of knee OA in the older women.

Characterization of the ankle dynamic joint stiffness as a function of gait speed for overground and treadmill walking.

The ankle dynamic joint stiffness (DJS), defined as the slope of the joint angle-moment plot, measures the resistance of the ankle joint to movement when the foot is in contact with the ground. DJS helps to stabilize the ankle joint, and its characterization helps to identify gait pathology and assist foot prosthesis design. This study analyzes the available gait dynamics data to obtain ankle DJS parameters for population groups according to age, gender, and gait speed for overground and treadmill walking. This study classified the groups into five walking speeds normalized using the Froude number. Herein, 12 ankle DJS parameters were determined. These include four linear segments: controlled plantar flexion (CP), early response phase (ERP), large response phase (LRP), and descending phase (DP), their corresponding turning points, the net mechanical work, the absorbed work, and the loop direction. Ankle dynamics data for 92 individuals was collected from two gait data repositories. The analysis reveals a notable disparity in stiffness values between overground and treadmill gait. Specifically, the CP stiffness is significantly higher for overground gait. In contrast, the DP stiffness displays an opposing pattern, with higher values observed during treadmill walking. A negative stiffness for LRP was found at fast speeds for all groups. The sorted data, analysis tools, and findings of this study are meant to help practitioners design prosthetic and rehabilitation devices based on age, gender, and walking environment at different gait speeds.

Effects of Gluteus Maximus Muscle Activity and Pelvic Width on Dynamic Frontal Plane Hip Joint Stiffness During Gait in Healthy Young Women.

Excessive hip adduction and internal rotation are abnormal movements that may lead to the onset and progression of patellofemoral pain. Previous studies have reported that lower dynamic frontal plane hip joint stiffness in the gait of women is associated with the magnitude of hip adduction and internal rotation angles. However, the factors contributing to the lack of dynamic frontal plane hip joint stiffness in the gait of young women are unclear. This study aims to investigate the factors affecting dynamic frontal plane hip joint stiffness during the weight-acceptance phase of the gait of healthy young women. Cross-sectional study. This study included 30 healthy women between the ages of 18 and 30years. The pelvic width/femur length ratio was calculated by dividing the pelvic width by the femur length. Data on hip kinematics and kinetics and activation of the gluteus maximus and medius, tensor fasciae latae, and adductor longus muscles during gait were collected using a motion capture system, force plates, and surface electromyography. Stepwise multiple regression analysis was conducted to determine the extent to which each independent factor affected dynamic frontal plane hip joint stiffness. In healthy young women, decreased dynamic frontal plane hip joint stiffness was associated with decreased muscle activity of the gluteus maximus during the gait, as well as greater pelvic width/femur length ratio. Women with a relatively great pelvic width relative to femur length may have more difficulty in producing dynamic frontal plane hip joint stiffness. However, increasing the muscle activity of the gluteus maximus may contribute to increased dynamic frontal plane hip joint stiffness.

Effect of toe-out gait modification on patellofemoral joint loading.

BackgroundToe-out gait has been proposed as a conservative treatment to reduce medial tibiofemoral joint loading. However, patellofemoral joint loading during toe-out gait is not yet understood. Research questionDoes the toe-out gait modification affect patellofemoral joint loading? MethodsSixteen healthy adults were enrolled in this study. The natural gait and toe-out gait were measured using a three-dimensional motion analysis and a force plate. The knee flexion angle and external knee flexion moment during the stance phase were calculated. Thus, dynamic knee joint stiffness, a proxy of patellofemoral joint loading, was defined as a linear regression of the knee flexion moment and knee flexion angle during the early stance. Additionally, the peak patellofemoral compressive force during the early stance was calculated using a musculoskeletal simulation. A paired t-test was used to compare these biomechanical parameters during the natural gait and toe-out gait. ResultsThe toe-out gait significantly increased the peak patellofemoral compressive force (mean difference = 0.37 BW, P = 0.017) and dynamic knee joint stiffness (mean difference = 0.07%BW*Ht/°, P = 0.001). The 1st peak of the knee flexion moment also significantly increased in the toe-out gait (mean difference = 1.01%BW*Ht, P = 0.003); however, the knee flexion angle did not change significantly (initial contact: mean difference = 1.7°, P = 0.078; peak: mean difference = 1.3°, P = 0.224). SignificanceToe-out gait increased the patellofemoral compressive force and dynamic knee joint stiffness because of increasing knee flexion moment, but not the knee flexion angle. When the toe-out gait is adapted, clinicians should pay attention to an increase in the patellofemoral joint loading.

Dynamic knee joint stiffness during running is associated with cartilage t1rho relaxation times 12- months post anterior cruciate ligament reconstruction

Dynamic knee joint stiffness during running is associated with cartilage t1rho relaxation times 12- months post anterior cruciate ligament reconstruction

Non-Parametric Nonlinear Parameter-Varying Parallel-Cascade Identification of Dynamic Joint Stiffness.

The paper presents a method to identify ankle joint dynamic stiffness during functional tasks where intrinsic and reflex stiffness change with a time-varying scheduling variable (SV), such as joint position or torque. The method models joint stiffness with two pathways: (1) A parameter-varying (PV) impulse response function (IRF) describing intrinsic stiffness; and (2) a reflex stiffness model comprising a PV static nonlinearity followed by a PV linear element. Monte-Carlo simulations demonstrated that the method accurately estimated all elements of the intrinsic and reflex pathways as they changed with a SV. Experimental results with a healthy individual subjected to large, imposed ankle movements demonstrated that: (a) Intrinsic stiffness changed substantially as a function of ankle position; elasticity was lowest near the mid-position and increased with either dorsiflexion or plantarflexion. (b) Reflex gain increased and the velocity threshold for reflex excitation decreased monotonically with ankle dorsiflexion. (c) Reflex dynamics resembled a second-order, low-pass system that was invariant with ankle position. (d) The identified PV Parallel-Cascade (PC) model accurately predicted the torque response to novel trajectories of ankle movement. The PV-PC method can accurately and reliably estimate how intrinsic and reflex stiffness change with a time-varying SV. The method is novel with multiple advantages: (a) It provides a unified algorithm that characterizes the changes in the parameters of all joint stiffness elements needed to understand their role in postural/movement control; (b) It is efficient requiring only two trials; (c) The models identified can predict the joint stiffness response to novel movements informing orthoses and prostheses design.

Dynamic knee joint stiffness during bilateral lower extremity landing 6 months after ACL reconstruction

BackgroundAnterior cruciate ligament (ACL) reconstructions are associated with long-term functional impairments. Improved understanding of dynamic knee joint stiffness and work may provide insights to help address these poor outcomes. Defining the relationship between knee stiffness, work and quadriceps muscle symmetry may reveal therapeutic targets. The purposes of this study were to investigate between-limb differences in knee stiffness and work during early phase landing 6-months after an ACL reconstruction. Additionally, we investigated relationships among symmetry of knee joint stiffness and work during early-phase landing and quadriceps muscle performance symmetry. MethodsTwenty-nine participants (17 M, 20.0 ± 5.3 years) were tested 6-months after ACL reconstruction. Motion capture analysis was used to assess between-limb differences in knee stiffness and work during the first 60 ms of a double-limb landing. Quadriceps peak strength and rate of torque development (RTD) were assessed with isometric dynamometry. Paired t-tests and Pearson’s product moment correlations were used to determine between-limb differences of knee mechanics and correlations of symmetry respectively. FindingsKnee joint stiffness and work were significantly reduced (p < 0.01, p < 0.01) in the surgical limb (0.021 ± 0.01 Nm*(deg*kg*m)−1, −0.085 ± 0.06 J*(kg*m) −1) compared to the uninvolved limb (0.045 ± 0.01 Nm*(deg*kg*m)−1, −0.256 ± 0.10 J*(kg*m) −1). Greater knee stiffness (51 ± 22%) and work (35 ± 21%) symmetry were significantly associated with greater RTD symmetry (44.5 ± 19.4%) (r = 0.43, p = 0.02; r = 0.45, p = 0.01) but not peak torque symmetry (62.9 ± 16.1%) (r = 0.32, p = 0.10; r = 0.34, p = 0.10). InterpretationDynamic stiffness and energy absorption are lower in the surgical knee during landing from a jump. Therapeutic interventions that target increasing quadriceps RTD may help optimize dynamic stability and energy absorption during landing.

Dynamic Joint Stiffness of the Knee in Post-Menopausal Women with and without Rheumatoid Arthritis

This study compared rheumatoid arthritis (RA) post-menopausal women with pathological involvement of the lower limb joints and age-matched post-menopausal women without RA regarding the dynamic joint stiffness (DJS) of knee during the stance phase of gait. Eighteen RA women and eighteen age-matched women were selected. Gait assessed through a three-dimensional motion analysis system synchronized with a force plate. Subjects walked barefoot at self-selected speed, and 14 valid trials were collected (comprising 7 left and 7 right foot-steps on force plate). The “moment of force—angle” plot of knee in sagittal plane was determined. The stance phase was split into three sub-phases: first knee flexion sub-phase (1st KFS); knee extension sub-phase (KES); second knee flexion sub-phase (2nd KFS). A linear model represented each sub-phase and DJS calculated by the slope. Model fitting was assessed through the coefficient of determination (R2). R2 values for both groups were higher than 0.8 during 1st KFS and KES but not during 2nd KFS. RA women yielded a higher DJS value during 2nd KFS (p &lt; 0.01). Concerning the other sub-phases, no differences were observed between groups. The findings suggested the splitting methodology used could be modelled by a linear “moment of force—angle” relationship, namely, during 1st KFS and KES. During 2nd KFS, RA women yielded a stiffer behavior.

Influence of dynamic stretching on ankle joint stiffness, vertical stiffness and running economy during treadmill running.

The purpose of the present study was to investigate whether and how dynamic stretching of the plantarflexors may influence running economy. A crossover design with a minimum of 48 h between experimental (dynamic stretching) and control conditions was used. Twelve recreational runners performed a step-wise incremental protocol to the limit of tolerance on a motorised instrumented treadmill. The initial speed was 2.3 m/s, followed by increments of 0.2 m/s every 3 min. Dynamic joint stiffness, vertical stiffness and running kinematics during the initial stage of the protocol were calculated. Running economy was evaluated using online gas-analysis. For each participant, the minimum number of stages completed before peak O2 uptake (V̇O2peak) common to the two testing conditions was used to calculate the gradient of a linear regression line between V̇O2 (y-axis) and speed (x-axis). The number of stages, which ranged between 4 and 8, was used to construct individual subject regression equations. Non-clinical forms of magnitude-based decision method were used to assess outcomes. The dynamic stretching protocol resulted in a possible decrease in dynamic ankle joint stiffness (−10.7%; 90% confidence limits ±16.1%), a possible decrease in vertical stiffness (−2.3%, ±4.3%), a possibly beneficial effect on running economy (−4.0%, ±8.3%), and very likely decrease in gastrocnemius medialis muscle activation (−27.1%, ±39.2%). The results indicate that dynamic stretching improves running economy, possibly via decreases in dynamic joint and vertical stiffness and muscle activation. Together, these results imply that dynamic stretching should be recommended as part of the warm-up for running training in recreational athletes examined in this study.

Metatarsophalangeal Joint Dynamic Stiffness During Toe Rocker Changes With Walking Speed.

Dynamic joint stiffness (or simply "stiffness") is a customization criteria used to tune mechanical properties of orthotic and prosthetic devices. This study examines metatarsophalangeal (MTP) joint stiffness during the toe-rocker phase of barefoot walking and establishes baseline characteristics of MTP joint stiffness. Ten healthy individuals walked at 4 speeds (0.4, 0.6, 0.8, and 1.0statures·s-1) over level ground. MTP sagittal plane joint angles and moments were calculated during the toe-rocker phase of stance. Least-squares linear regressions were conducted on the MTP moment versus angle curve to determine joint stiffness during early toe rocker and late toe rocker. Multilevel linear models were used to test for statistically significant differences between conditions. Early toe rocker stiffness was positive, while late toe rocker was negative. Both early toe rocker and late toe rocker stiffness increased in magnitude significantly with speed. This study establishes baseline characteristics of MTP joint stiffness in healthy walking, which previously had not been examined through a range of controlled walking speeds. This information can be used in the future as design criteria for orthotic and prosthetic ankle and ankle-foot devices that can imitate, support, and facilitate natural human foot motion during walking better than existing devices.

Extended-state-observer-based adaptive control of flexible-joint space manipulators with system uncertainties

In this paper, an extended-state-observer-based adaptive controller is proposed for flexible-joint space manipulators (FJSM) to accurately track trajectories while stabilizing bases in the presence of dynamic uncertainties and joint stiffness uncertainties. The dynamic model of a FJSM is established, and its state-spaced representation is obtained by introducing an error vector and a sliding mode surface vector as state variables. Besides, an extended state observer (ESO) is designed to guarantee the precise estimation of the manipulator’s velocity states as well as the joint stiffness uncertainties. Based on the ESO and the state-spaced representation, an adaptive controller is generated by implementing backstepping method, where the dynamic uncertainties are compensated by a Radial Basis Function neural network (RBFNN) and the joint stiffness uncertainties are eliminated by the estimation of the ESO. The stabilities of the ESO-based adaptive controller are validated by Lyapunov theory. Several numerical simulations were conducted, and the simulation results verifies the effectiveness of the proposed controller.

Dynamic Knee Joint Stiffness During Bilateral Lower Extremity Landing 6 Months after ACL Reconstruction

Dynamic Knee Joint Stiffness During Bilateral Lower Extremity Landing 6 Months after ACL Reconstruction

The Effect of Functional Biomechanics Garment for Walking.

The purpose of this study was to investigate the effects of a functional biomechanics garment (FBG) with a lower extremity assist function. 32 healthy male participants were included in this study. Participants were divided into an FBG with taping function group (FBG group) and a compression garment group (CG group). Cadence (steps/min), step length (m), and usual walking speed (m/s) were measured as spatio-temporal data. Kinetics, kinematics data, and dynamic joint stiffness (DJS) of the lower extremity were calculated using a three-dimensional gait analysis system. The FBG group showed significantly faster walking speed (FBG, 1.54 ± 0.12 m/s; CG, 1.42 ± 0.15 m/s, p < 0.05) and reduced hip DJS in terminal stance (FBG, 0.033 ± 0.014 Nm/kg/degree; CG: 0.049 ± 0.016 Nm/kg/degree, p < 0.05) compared to the CG group. The FBG decreased hip DJS in the terminal stance and affected walking speed. The passive elastic moment generated by the high elasticity part of the hip joint front in the FBG supported the internal hip flexion moment. Therefore, our FBG has a biomechanical effect. The FBG may be useful as a tool to promote health activities.

Effects of sex and walking speed on the dynamic stiffness of lower limb joints

Fast walking may require a non-uniform change of dynamic stiffness among lower limb joints to deal with this daily task’s demands. The change of dynamic joint stiffness may be distinct between females and males. This study aimed to test for differences in dynamic stiffness among lower limb joints in response to increased walking speed in males and females. Thirty-five participants walked in two randomized conditions: self-selected speed and fast speed (25% greater than the self-selected speed). Dynamic stiffnesses of the ankle, knee, and hip were calculated as the linear slope of the moment–angle curve’s regression line during their major power absorption phase of the walking cycle. The comparison between conditions showed that the knee (p < 0.001) and hip (p = 0.031) increased their stiffness at the fast compared to self-selected speed. Ankle stiffness was not different between conditions (p = 0.818). The comparison among joints across speeds showed that the knee had a greater increase than the ankle (p = 0.001) and hip (p < 0.001), with no difference between ankle and hip (p = 0.081). The sex of the participant influenced only the ankle stiffness, in which males had greater stiffness than females (p = 0.008). These findings demonstrated that the lower limb joints changed their dynamic stiffness differently, and only the ankle stiffness was influenced by sex. The non-uniform adjustments of stiffness may provide the necessary stability and allow the individual to deal with greater demand for walking fast.

Task dependent changes in mechanical and biomechanical measures result from manipulating stiffness settings in a prosthetic foot

BackgroundAdaptation of lower limb function to different gait tasks is inherently not as effective among individuals with lower limb amputation as compared to able-bodied individuals. Varying stiffness of a prosthetic foot may be a way of facilitating gait tasks that require larger ankle joint range of motion. MethodsThree stiffness settings of a novel prosthetic foot design were tested for level walking at three speeds as well as for 7,5° incline and decline walking. Outcome measures, describing ankle range of motion and ankle dynamic joint stiffness were contrasted across the three stiffness settings. Standardized mechanical tests were done for the hindfoot and forefoot. FindingsDorsiflexion angle was incrementally increased with a softer foot and a faster walking speed / higher degree of slope. The concurrent dynamic joint stiffness exhibited a less systematic change, especially during INCLINE and DECLINE walking. The small difference seen between the stiffness settings for hindfoot loading limits analysis for the effects of stiffness during weight acceptance, however, a stiffer foot significantly restricted plantarflexion during DECLINE. InterpretationsVarying stiffness settings within a prosthetic foot does have an effect on prosthetic foot dynamics, and differences are task dependent, specifically in parameters involving kinetic attributes. When considering the need for increased ankle range of motion while performing more demanding gait tasks, a foot that allows the users themselves to adjust stiffness according to the task at hand may be of benefit for active individuals, possibly enhancing the user's satisfaction and comfort during various daily activities.

Load Carriage During Walking Increases Dynamic Stiffness at Distal Lower Limb Joints.

The addition of a load during walking requires changes in the movement pattern. The investigation of the dynamic joint stiffness behavior may help to understand the lower limb joints' contribution to these changes. This study aimed to investigate the dynamic stiffness of lower limb joints in response to the increased load carried while walking. Thirteen participants walked in two conditions: unloaded (an empty backpack) and loaded (the same backpack plus added mass corresponding to 30% of body mass). Dynamic stiffness was calculated as the linear slope of the regression line on the moment-angle curve during the power absorption phases of the ankle, knee, and hip in the sagittal plane. The results showed that ankle (P = .002) and knee (P < .001) increased their dynamic stiffness during loaded walking compared with unloaded, but no difference was observed at the hip (P = .332). The dynamic stiffness changes were different among joints (P < .001): ankle and knee changes were not different (P < .992), but they had a greater change than hip (P < .001). The nonuniform increases in lower limb joint dynamic stiffness suggest that the ankle and knee are critical joints to deal with the extra loading.