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Schematic of segment and corresponding joint angle coordinate systems. Joint centres are represented by white circles. The solid lines indicate 0 degrees, + and − designate positive and negative angles, respectively.
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The muscles surrounding the ankle, knee and hip joints provide 42, 16 and 42%, respectively, of the total leg positive power required to walk on level ground at various speeds. However, each joint's contribution to leg work when walking up/downhill at a range of speeds is not known. Determining each biological joint's contribution to leg work over...
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Citations
... Much of this additional mechanical energy is generated by the hip [2]. During uphill walking, the ankle joint needs to release more energy to propel the body forward, while the absorption of energy by the ankle remains essentially constant [3]. For the knee joint, the angle of activity was greater when running uphill than when running on level ground [4]. ...
Background: During city running or marathon races, shifts in level ground and up-and-down slopes are regularly encountered, resulting in changes in lower limb biomechanics. The longitudinal bending stiffness of the running shoe affects the running performance. Purpose: This research aimed to investigate the biomechanical changes in the lower limbs when transitioning from level ground to an uphill slope under different longitudinal bending stiffness (LBS) levels in running shoes. Methods: Fifteen male amateur runners were recruited and tested while wearing three different LBS running shoes. The participants were asked to pass the force platform with their right foot at a speed of 3.3 m/s ± 0.2. Kinematics data and GRFs were collected synchronously. Each participant completed and recorded ten successful experiments per pair of shoes. Results: The range of motion in the sagittal of the knee joint was reduced with the increase in the longitudinal bending stiffness. Positive work was increased in the sagittal plane of the ankle joint and reduced in the keen joint. The negative work of the knee joint increased in the sagittal plane. The positive work of the metatarsophalangeal joint in the sagittal plane increased. Conclusion: Transitioning from running on a level surface to running uphill, while wearing running shoes with high LBS, could lead to improved efficiency in lower limb function. However, the higher LBS of running shoes increases the energy absorption of the knee joint, potentially increasing the risk of knee injuries. Thus, amateurs should choose running shoes with optimal stiffness when running.
... For walking uphill, the biological ankle also provides additional positive work to move the body's center of mass up the slope against gravity. During downhill walking, the lower limbs mostly absorb energy and generate less positive work at the joints as the center of mass is lowered [3][4][5][6]. ...
... For walking downhill, a prosthesis with a toe joint could aid LLPUs by providing flexibility in the device during late stance to support lowering their center of mass. The potential reduction in prosthetic Push-off power may be inconsequential or even beneficial when walking downhill as there is less need to generate positive power with the lower limbs and specifically the ankle joint [3][4][5][6]. However, the impact of incorporating a flexible toe joint into a prothesis for sloped walking has never been tested. ...
... We expected positive prosthesis Push-off work to be reduced for the Flexible configuration compared to the Locked configuration for both incline and decline walking. We expected LLPUs to prefer the Locked configuration for incline walking due to the increased amount of positive work (from the ankle and at the center-of-mass level) that is necessary to ascend ramps [3][4][5][6]. For decline walking, we expected users to prefer the Flexible configuration as it provides an additional degree of flexibility during late stance to assist LLPUs in lowering their center of mass. ...
Walking on sloped surfaces is challenging for many lower limb prosthesis users, in part due to the limited ankle range of motion provided by typical prosthetic ankle-foot devices. Adding a toe joint could potentially benefit users by providing an additional degree of flexibility to adapt to sloped surfaces, but this remains untested. The objective of this study was to characterize the effect of a prosthesis with an articulating toe joint on the preferences and gait biomechanics of individuals with unilateral below-knee limb loss walking on slopes. Nine active prosthesis users walked on an instrumented treadmill at a +5° incline and -5° decline while wearing an experimental foot prosthesis in two configurations: a Flexible toe joint and a Locked-out toe joint. Three participants preferred the Flexible toe joint over the Locked-out toe joint for incline and decline walking. Eight of nine participants went on to participate in a biomechanical data collection. The Flexible toe joint decreased prosthesis Push-off work by 2 Joules during both incline (p = 0.008; g = -0.63) and decline (p = 0.008; g = -0.65) walking. During incline walking, prosthetic limb knee flexion at toe-off was 3° greater in the Flexible configuration compared to the Locked (p = 0.008; g = 0.42). Overall, these results indicate that adding a toe joint to a passive foot prosthesis has relatively small effects on joint kinematics and kinetics during sloped walking. This study is part of a larger body of work that also assessed the impact of a prosthetic toe joint for level and uneven terrain walking and stair ascent/descent. Collectively, toe joints do not appear to substantially or consistently alter lower limb mechanics for active unilateral below-knee prosthesis users. Our findings also demonstrate that user preference for passive prosthetic technology may be both subject-specific and task-specific. Future work could investigate the inter-individual preferences and potential benefits of a prosthetic toe joint for lower-mobility individuals.
... Rapid, unanticipated changes in ground height during hopping have also shown an elevation in negative knee power [19]. The knee emerges as the primary source of negative joint work during downhill walking [13] and running [20]. Knee extensors (e.g., quadriceps) generate greater eccentric work and thus compensatory energy dissipation during the braking phase in the drop-step to control knee flexion and mitigate the vertical drop of the center of mass. ...
Despite evidence on trunk flexion’s impact on locomotion mechanics, its role in modulating lower-limb energetics during perturbed running remains underexplored. Therefore, we investigated posture-induced power redistribution in the lower-limb joints (hip, knee, and ankle), along with the relative contribution from each joint to total lower-limb average positive and negative mechanical powers (i.e., over time) during perturbed running. Twelve runners (50% female) ran at self-selected (~15°) and three more sagittal trunk inclinations (backward, ~0°; low forward, ~20°; high forward, ~25°) on a custom-built runway, incorporating both a level surface and a 10 cm visible drop-step positioned midway, while simultaneously recording three-dimensional kinematics and kinetics. We used inverse dynamics analysis to determine moments and powers in lower-limb joints. Increasing the trunk forward inclination yielded the following changes in lower-limb mechanics: a) an elevation in total positive power with a distoproximal shift and a reduction in total negative power; b) systematic increases in hip positive power, coupled with decreased and increased contribution to total negative (during level-step) and positive (during drop-step) powers, respectively; c) reductions in both negative and positive knee powers, along with a decrease in its contribution to total positive power. Regardless of the trunk posture, accommodating drop-steps while running demands elevated total limb negative and positive powers with the ankle as a primary source of energy absorption and generation. Leaning the trunk more forward induces a distoproximal shift in positive power, whereas leaning backward exerts an opposing influence on negative power within the lower-limb joints.
... Characteristic gait changes have been reported for walking on slopes, such as changes in the contribution of the ankle joint to leg work [8]. In addition, uphill walking on a treadmill increases hip and knee flexion angles during the stance phase, as well as the forward tilt of the thorax [9]. ...
Background
Monitoring of gait patterns by insoles is popular to study behavior and activity in the daily life of people and throughout the rehabilitation process of patients. Live data analyses may improve personalized prevention and treatment regimens, as well as rehabilitation. The M-shaped plantar pressure curve during the stance phase is mainly defined by the loading and unloading slope, 2 maxima, 1 minimum, as well as the force during defined periods. When monitoring gait continuously, walking uphill or downhill could affect this curve in characteristic ways.
Objective
For walking on a slope, typical changes in the stance phase curve measured by insoles were hypothesized.
Methods
In total, 40 healthy participants of both sexes were fitted with individually calibrated insoles with 16 pressure sensors each and a recording frequency of 100 Hz. Participants walked on a treadmill at 4 km/h for 1 minute in each of the following slopes: −20%, −15%, −10%, −5%, 0%, 5%, 10%, 15%, and 20%. Raw data were exported for analyses. A custom-developed data platform was used for data processing and parameter calculation, including step detection, data transformation, and normalization for time by natural cubic spline interpolation and force (proportion of body weight). To identify the time-axis positions of the desired maxima and minimum among the available extremum candidates in each step, a Gaussian filter was applied (σ=3, kernel size 7). Inconclusive extremum candidates were further processed by screening for time plausibility, maximum or minimum pool filtering, and monotony. Several parameters that describe the curve trajectory were computed for each step. The normal distribution of data was tested by the Kolmogorov-Smirnov and Shapiro-Wilk tests.
Results
Data were normally distributed. An analysis of variance with the gait parameters as dependent and slope as independent variables revealed significant changes related to the slope for the following parameters of the stance phase curve: the mean force during loading and unloading, the 2 maxima and the minimum, as well as the loading and unloading slope (all P<.001). A simultaneous increase in the loading slope, the first maximum and the mean loading force combined with a decrease in the mean unloading force, the second maximum, and the unloading slope is characteristic for downhill walking. The opposite represents uphill walking. The minimum had its peak at horizontal walking and values dropped when walking uphill and downhill alike. It is therefore not a suitable parameter to distinguish between uphill and downhill walking.
Conclusions
While patient-related factors, such as anthropometrics, injury, or disease shape the stance phase curve on a longer-term scale, walking on slopes leads to temporary and characteristic short-term changes in the curve trajectory.
... Compared to horizontal displacement errors on the order of 0.5-1% of stride length [11,18,26,41], higher vertical errors around 1-2% are common [11,18,19,21,26]. Vertical error is especially important in interpreting the reconstructed movement because of the influence of ground incline on biomechanical outcomes such as limb and joint mechanics [42][43][44][45][46], muscle behavior [47,48], and energetic cost [49]. Moreover, the direction can be either rising or falling in different circumstances but tends to be consistent within specific bouts and behaviors. ...
Motion reconstruction using wearable sensors enables broad opportunities for gait analysis outside laboratory environments. Inertial Measurement Unit (IMU)-based foot trajectory reconstruction is an essential component of estimating the foot motion and user position required for any related biomechanics metrics. However, limitations remain in the reconstruction quality due to well-known sensor noise and drift issues, and in some cases, limited sensor bandwidth and range. In this work, to reduce drift in the height direction and handle the impulsive velocity error at heel strike, we enhanced the integration reconstruction with a novel kinematic model that partitions integration velocity errors into estimates of acceleration bias and heel strike vertical velocity error. Using this model, we achieve reduced height drift in reconstruction and simultaneously accomplish reliable terrain determination among level ground, ramps, and stairs. The reconstruction performance of the proposed method is compared against the widely used Error State Kalman Filter-based Pedestrian Dead Reckoning and integration-based foot-IMU motion reconstruction method with 15 trials from six subjects, including one prosthesis user. The mean height errors per stride are 0.03±0.08 cm on level ground, 0.95±0.37 cm on ramps, and 1.27±1.22 cm on stairs. The proposed method can determine the terrain types accurately by thresholding on the model output and demonstrates great reconstruction improvement in level-ground walking and moderate improvement on ramps and stairs.
... To effectively unload or augment the biological joint, knowledge of joint biomechanics is typically incorporated into the design or control of the exo. Generally speaking, the research field has a good comprehension of lower limb joint-level biomechanics, including: dynamic (quasi-) stiffness [2][3][4][5][6] ; distribution of work across the joints [7][8][9] ; and how factors such as speed, terrain, and load change the joint dynamics. [10][11][12] However, skeletal muscles are the actual actuators that generate movement. ...
Lower limb exoskeletons and exosuits (“exos”) are traditionally designed with a strong focus on mechatronics and actuation, whereas the “human side” is often disregarded or minimally modeled. Muscle biomechanics principles and skeletal muscle response to robot-delivered loads should be incorporated in design/control of exos. In this narrative review, we summarize the advances in literature with respect to the fusion of muscle biomechanics and lower limb exoskeletons. We report methods to measure muscle biomechanics directly and indirectly and summarize the studies that have incorporated muscle measures for improved design and control of intuitive lower limb exos. Finally, we delve into articles that have studied how the human–exo interaction influences muscle biomechanics during locomotion. To support neurorehabilitation and facilitate everyday use of wearable assistive technologies, we believe that future studies should investigate and predict how exoskeleton assistance strategies would structurally remodel skeletal muscle over time. Real-time mapping of the neuromechanical origin and generation of muscle force resulting in joint torques should be combined with musculoskeletal models to address time-varying parameters such as adaptation to exos and fatigue. Development of smarter predictive controllers that steer rather than assist biological components could result in a synchronized human–machine system that optimizes the biological and electromechanical performance of the combined system.
... Indeed during locomotion on a level surface for a range of steady-state speeds, certain joints like the ankle do net-positive work (produce energy) [2,13], while the foot, particularly the heel, performs a large portion of the net negative work (energy dissipation) during early stance [14][15][16][17]. Studies have previously explored how joints modulate work and power over a range of steady-state speeds on level or sloped surfaces or/and by changing the body's net mechanical energy requirements [2,6,[18][19][20][21]. However, the mechanical adaptability of the human foot has been examined primarily in single-stepping tasks [22] or over locomotor tasks on a level surface, like running [14] and walking with added mass [15]. ...
When humans walk on slopes, the ankle, knee, and hip joints modulate their mechanical work to accommodate the mechanical demands. Yet, it is unclear if the foot modulates its work output during uphill and downhill walking. Therefore, we quantified the mechanical work performed by the foot and its subsections of twelve adults walked on five randomized slopes (-10°, -5°, 0°, +5°, +10°). We estimated the work of distal-to-hindfoot and distal-to-forefoot structures using unified deformable segment analysis and the work of the midtarsal, ankle, knee, and hip joints using a six-degree-of-freedom model. Further, using a geometric model, we estimated the length of the plantar structures crossing the longitudinal arch while accounting for the first metatarsophalangeal wrapping length. We hypothesized that compared to level walking, downhill walking would increase negative and net-negative work magnitude, particularly at the early stance phase, and uphill walking would increase the positive work, particularly at the mid-to-late stance phase. We found that downhill walking increased the magnitude of the foot's negative and net-negative work, especially during early stance, highlighting its capacity to absorb impacts when locomotion demands excessive energy dissipation. Notably, the foot maintained its net dissipative behavior between slopes; however, the ankle, knee, and hip shifted from net energy dissipation to net energy generation when changing from downhill to uphill. Such results indicate that humans rely more on joints proximal to the foot to modulate the body's total mechanical energy. Uphill walking increased midtarsal's positive and distal-to-forefoot negative work in near-equal amounts. That coincided with the prolonged lengthening and delayed shortening of the plantar structures, resembling a spring-like function that possibly assists the energetic demands of locomotion during mid-to-late stance. These results broaden our understanding of the foot's mechanical function relative to the leg's joints and could inspire the design of wearable assistive devices that improve walking capacity.
... When humans walk they seemingly minimize the energy spent per distance travelled, i.e., the metabolic cost of transport (MCOT) (Bertram & Ruina, 2001;Ralston, 1958). Ankle plantar flexors, hip flexors and hip extensors provide the bulk of the required energy (Farris & Sawicki, 2012;Montgomery & Grabowski, 2018;Winter, 1983). Impairment of ankle plantar flexors or hip muscles may result in gait adaptations and reduced energy efficiency (Farris et al., 2015;Huang et al., 2015;Stevens, Podeszwa & Tulchin-Francis, 2019). ...
In human walking, power for propulsion is generated primarily via ankle and hip muscles. The addition of a ‘passive’ hip spring to simple bipedal models appears more efficient than using only push-off impulse, at least, when hip spring associated energetic costs are not considered. Hip flexion and retraction torques, however, are not ‘free’, as they are produced by muscles demanding metabolic energy. Studies evaluating the inclusion of hip actuation costs, especially during the swing phase, and the hip actuation’s energetic benefits are few and far between. It is also unknown whether these possible benefits/effects may depend on speed. We simulated a planar flat-feet model walking stably over a range of speeds. We asked whether the addition of independent hip flexion and retraction remains energetically beneficial when considering work-based metabolic cost of transport (MCOT) with different efficiencies of doing positive and negative work. We found asymmetric hip actuation can reduce the estimated MCOT relative to ankle actuation by up to 6%, but only at medium speeds. The corresponding optimal strategy is zero hip flexion and some hip retraction actuation. The reason for this reduced MCOT is that the decrease in collision loss is larger than the associated increase in hip negative work. This leads to a reduction in total positive mechanical work, which results in an overall lower MCOT. Our study shows how ankle actuation, hip flexion, and retraction actuation can be coordinated to reduce MCOT.
... Thus, use of the BiOM compared to each subject's ESAR prosthesis did not systematically decrease iEMG, peak EMG or muscle activity burst duration on uphill slopes and had some effects on downhill slopes. To walk uphill compared to level ground, non-amputees and people with TTA increase leg extensor muscle activity to increase the positive mechanical work produced by the legs and raise the COM [10,[20][21][22]. To walk downhill compared to level ground, non-amputees and people with TTA increase knee extensor muscle activity to increase the magnitude of negative mechanical work absorbed by the legs and lower the COM [20][21][22]. ...
... To walk uphill compared to level ground, non-amputees and people with TTA increase leg extensor muscle activity to increase the positive mechanical work produced by the legs and raise the COM [10,[20][21][22]. To walk downhill compared to level ground, non-amputees and people with TTA increase knee extensor muscle activity to increase the magnitude of negative mechanical work absorbed by the legs and lower the COM [20][21][22]. When people with TTA walked on level, uphill and downhill slopes, they exhibited the same changes in muscle activity patterns as non-amputees [10]. ...
People with transtibial amputation (TTA) using passive-elastic prostheses have greater leg muscle activity and metabolic cost during level-ground and sloped walking than non-amputees. Use of a stance-phase powered (BiOM) versus passive-elastic prosthesis reduces metabolic cost for people with TTA during level-ground, +3° and +6° walking. Metabolic cost is associated with muscle activity, which may provide insight into differences between prostheses. We measured affected leg (AL) and unaffected leg (UL) muscle activity from ten people with TTA (6 males, 4 females) walking at 1.25 m s ⁻¹ on a dual-belt force-measuring treadmill at 0°, ±3°, ±6° and ±9° using their own passive-elastic and the BiOM prosthesis. We compared stride average integrated EMG (iEMG), peak EMG and muscle activity burst duration. Use of the BiOM increased UL lateral gastrocnemius iEMG on downhill slopes and AL biceps femoris on +6° and +9° slopes, and decreased UL rectus femoris on uphill slopes, UL vastus lateralis on +6° and +9°, and soleus and tibialis anterior on a +9° slope compared to a passive-elastic prosthesis. Differences in leg muscle activity for people with TTA using a passive-elastic versus stance-phase powered prosthesis do not clearly explain differences in metabolic cost during walking on level ground and slopes.
... Hip flexion promotes the motion of the swing leg in preparation for receiving the energy of the stance leg, and taking on the role of next stance leg [2]- [4]. In the process, hip flexor and extensor muscles generate a large amount of biological work, thus leading to significant metabolic power expenditure [5]- [7]. Studies showed that hip torque actuation can reduce the energy cost and improve the stability of walking [8], [9]. ...
Hip-assisted soft exosuits have been reported for their effect on reducing the metabolic power of human walking. Currently, most studies focus on uni-directional assistance (HF: hip flexion, or HE: hip extension). This paper investigates the effect of bi-directional assistance (HFE: hip flexion and extension) on the biomechanics and physiology of the wearer for understanding the potential benefits in synergistic effect of multi-muscle assistance. A belt-type soft exosuit was developed to provide the bi-directional assistance for augmenting walking. The assistance strategy was presented by imitating the contraction mechanisms of hip flexor and extensor muscles in walking. Tests on 8 healthy subjects were conducted and the results were compared with traditional uni-directional assistance. Metabolic powers, muscle activities, kinematics, and kinetics were measured and analyzed. Results showed that HFE assistance reduced the metabolic power by 7% and 12.4% relative to no exosuit and assistance turned off, respectively, larger than the sum of HF and HE. Furthermore, HFE reduced more total joint positive biological work and the activity of more related muscles, and at the same time increased upward and downward accelerations of body mass center, promoting walking energy exchange. These findings demonstrate that bi-directional assistance by combining hip flexion and extension has a significant synergistic effect on augmenting human walking as well as a benefit of increasing biological efficiency.
