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In this paper, we review what mechanisms are used to stabilize human bipedal walking. Based on mechanical reasoning, potential mechanisms to control the body center of mass trajectory are modulation of foot placement, stance leg control by modulation of ankle moments and push-off forces, and modulations of the body's angular momentum. The first two mechanisms and especially the first are dominant in controlling center of mass accelerations during gait, while angular momentum control plays a lesser role, but may be important to control body alignment and orientation. The same control mechanisms stabilize both steady-state and perturbed gait in both the mediolateral and antero-posterior directions. Control is at least in part active and is affected by proprioceptive, visual and vestibular information. Results support that this reflects a feedback process in which sensory information is used to obtain an estimate of the center of mass state based on which foot placement and ankle moments are modulated. These active feedback mechanisms suggest training approaches for populations at risk of falling, through perturbations, augmented feedback, or constraining one mechanism to train the other mechanisms. [ABSTRACT FROM AUTHOR]

Background: Individuals with obesity demonstrate deficits in postural stability, leading to increased fall risks. Controlling whole-body angular momentum is essential for maintaining postural stability during walking and preventing falls. However, it is unknown how obesity impacts whole-body angular momentum during walking.Research Purpose: To investigate the change in angular momentum about the body's COM during walking in individuals with different degrees of obesity.Methods: Thirty-eight young adults with different body mass index (BMI) scores walked barefoot at their preferred speed on a treadmill for 2 min. The whole-body angular momentum has been quantified from ground reaction force and moment data to capture the rotational behavior of walking in individuals with obesity without relying solely on placing markers on anatomical landmarks.Results: We found that adults with higher BMI scores walked slower with shorter step length, wider step width, and longer double support time (ps<.01). Ranges of the frontal- and transverse-plane angular momentum were greater in adults with higher BMI scores (ps<.01), while no difference was observed between BMI groups in the total sum of changes in whole-body angular momentum in any plane (ps>.05).Significance: Obesity not only decreased walking speed but also limited the ability to control mediolateral stability during walking. Investigating how obesity affects whole-body angular momentum may help better understand why adults with obesity have atypical gait with poor balance, address fall risk factors, and facilitate participation in physical activities. [ABSTRACT FROM AUTHOR]

This research tested a reproducible uneven walkway designed to destabilize human gait. Ten participants walked 30 times over even and uneven (7.3 x .08 m, sequentially-placed wooden blocks in a rotating pattern, 1-cm thick rubber mat) walkways. A full-body marker set and 8-camera motion capture system recorded limb kinematics. MatLab 2013b was used to calculate measures of gait stability: angular momentum, margin of stability, step width variability, CoM height, toe clearance, lateral arm swing. The minimum number of strides necessary to minimize intraparticipant variability was calculated via the interquartile range/median ratio (IMR) at 25% and 10% thresholds for each measure. A paired t test tested for significance between terrains (P < .05). The uneven walkway significantly destabilized gait as seen by increases in: coronal and sagittal plane angular momentum, step width variability, and toe clearance. We found no significant difference with the margin of stability between the 2 terrains possibly due to compensatory strategies (eg, lateral arm swing, trunk sway, step width). Recording a minimum of 10 strides per subject will keep each variable between the 25% and 10% IMR thresholds. In conclusion, the uneven walkway design significantly destabilizes human gait and at least 10 strides should be collected per subject. [ABSTRACT FROM AUTHOR]

Bipedal walking locomotion is one of the characteristics of human behavior. Both the lower body and the upper body (trunk) behaviors affect walking characteristics. To achieve a suitable gait, it is important to understand the effect of the trunk behavior. Therefore, in this paper, the effects of three types of trunk swinging behavior on planar bipedal gait in a model with an upper body -- forward swinging, backward swinging, and no swinging -- were evaluated using numerical simulations. To reduce control inputs and reflect the effect of upper body behavior, an underactuated bipedal walker without knee joints was adopted. This walker walked down a gentle slope using only hip actuation between the stance leg and the trunk. As a result, unique gait characteristics that depended on the direction of the trunk swinging behavior were found, including a longer step length and a lower-frequency gait with forward trunk swinging behavior and a shorter step length and higher-frequency gait with smaller angular momentum with backward trunk swinging behavior. [ABSTRACT FROM AUTHOR]

Background: Turning is a frequently performed, asymmetric task of daily living. The asymmetric nature makes turning challenging to perform while maintaining balance.Research Question: How do healthy individuals maintain dynamic balance, quantified as whole-body angular momentum, during a 90-degree turn compared to straight-line walking?Methods: The kinematics of sixteen healthy individuals were tracked during walking in a straight-line and during left and right 90-degree turns at a comfortable pace. Whole-body and segment angular momenta were calculated and the relative contributions of the legs, arms, pelvis and head/trunk to whole-body angular momentum were evaluated.Results: Average whole-body angular momentum was different during turning compared to straight-line walking in all planes of motion. The initiation of a turn required generation of whole body angular momentum in all three planes of motion, which was counteracted at the end of the turn by a generation of angular momentum in the opposite direction in the frontal and sagittal planes. Transverse plane momentum was always directed in the turn direction. All segment groups, except for the inside leg, had a greater magnitude of angular momentum during turning compared to straight-line walking. The outside leg and head/trunk segments were the largest contributors to frontal and transverse plane whole-body angular momentum.Significance: Understanding how body segments contribute to maintaining balance during a 90-degree turn can be useful for designing rehabilitation paradigms for people who have difficulty turning or impaired balance. [ABSTRACT FROM AUTHOR]

Background Patients with transtibial amputation adopt trunk movement compensations that alter effort and increase the risk of developing low back pain. However, the effort required to achieve high-demand tasks, such as step ascent and descent, remains unknown. Methods Kinematics were collected during bilateral step ascent and descent tasks from two groups: 1) seven patients with unilateral transtibial amputation and 2) seven healthy control subjects. Trunk kinetic effort was quantified using translational and rotational segmental moments (time rate of change of segmental angular momentum). Peak moments during the loading period were compared across limbs and across groups. Findings During step ascent, patients with transtibial amputation generated larger sagittal trunk translational moments when leading with the amputated limb compared to the intact limb ( P = 0.01). The amputation group also generated larger trunk rotational moments in the frontal and transverse planes when leading with either limb compared to the healthy group ( P = 0.01, P < 0.01, respectively). During step descent, the amputation group generated larger trunk translational and rotational moments in all three planes when leading with the intact limb compared to the healthy group ( P < 0.017). Interpretation This investigation identifies how differing trunk movement compensations, identified using the separation of angular momentum, require higher kinetic effort during stepping tasks in patients with transtibial amputation compared to healthy individuals. Compensations that produce identified increased and asymmetric trunk segmental moments, may increase the risk of the development of low back pain in patients with amputation. [ABSTRACT FROM AUTHOR]

Backward walking training has been reported to improve gait speed and balance post-stroke. However, it is not known if gains are achieved through recovery of the paretic limb or compensations from the nonparetic limb. The purpose of this study was to compare the influence of backward locomotor training (BLT) versus forward locomotor training (FLT) on gait speed and dynamic balance control, and to quantify the underlying mechanisms used to achieve any gains. Eighteen participants post chronic stroke were randomly assigned to receive 18 sessions of either FLT (n = 8) or BLT (n = 10). Pre- and post-intervention outcomes included gait speed (10-meter Walk Test) and forward propulsion (time integral of anterior-posterior ground-reaction-forces during late stance for each limb). Dynamic balance control was assessed using clinical (Functional Gait Assessment) and biomechanical (peak-to-peak range of whole-body angular-momentum in the frontal plane) measures. Balance confidence was assessed using the Activities-Specific Balance Confidence scale. While gait speed and balance confidence improved significantly within the BLT group, these improvements were associated with an increased nonparetic limb propulsion generation, suggesting use of compensatory mechanisms. Although there were no improvements in gait speed within the FLT group, paretic limb propulsion generation significantly improved post-FLT, suggesting recovery of the paretic limb. Neither training group improved in dynamic balance control, implying the need of balance specific training along with locomotor training to improve balance control post-stroke. Despite the within-group differences, there were no significant differences between the FLT and BLT groups in the achieved gains in any of the outcomes. [ABSTRACT FROM AUTHOR]

Mediolateral balance control during walking is a challenging task in post-stroke hemiparetic individuals. To detect and treat dynamic balance disorders, it is important to assess balance using reliable methods. The Berg Balance Scale (BBS), Dynamic Gait Index (DGI), margin-of-stability (MoS), and peak-to-peak range of angular-momentum ( H ) are some of the most commonly used measures to assess dynamic balance and fall risk in clinical and laboratory settings. However, it is not clear if these measures lead to similar conclusions. Thus, the purpose of this study was to assess dynamic balance in post-stroke hemiparetic individuals using BBS, DGI, MoS and the range of H and determine if these measure are correlated. BBS and DGI were collected from 19 individuals post-stroke. Additionally, kinematic and kinetic data were collected while the same individuals walked at their self-selected speed. MoS and the range of H were calculated in the mediolateral direction for each participant. Correlation analyses revealed moderate associations between all measures. Overall, a higher range of angular-momentum was associated with a higher MoS, wider step width and lower BBS and DGI scores, indicating poor balance control. Further, only the MoS from the paretic foot placement, but not the nonparetic foot, correlated with the other balance measures. Although moderate correlations existed between all the balance measures, these findings do not necessarily advocate the use of a single measure as each test may assess different constructs of dynamic balance. These findings have important implications for the use and interpretation of dynamic balance assessments. [ABSTRACT FROM AUTHOR]

Tripping over obstacles is one of the main causes of falls. One potential hazard to actually fall when tripped is inadequate foot landing. Adequate landing is required to control the body's angular momentum, while avoiding dangerous surfaces (slippery patch, uneven ground). To avoid such dangers, foot trajectory needs to be controlled by inhibiting and adjusting the initiated recovery foot path during a tripping reaction. We investigated whether such adjustments can be made without jeopardizing balance recovery. Sixteen healthy young adults (25.1 ± 3.2 years) walked at their comfortable speed over a walkway equipped with 14 hidden obstacles. Participants were tripped 10 times in between a random number of normal walking trials; five trips included a projection of a forbidden zone (FZ, 30 × 50 cm) at the subject's preferred landing position. Participants were instructed to land their recovery foot outside the FZ, if the FZ was presented. Responses were evaluated in terms of foot position and body angular momentum at and following recovery foot landing. Participants successfully landed their recovery foot outside the FZ in 80 % of trials, using strategies of either shortening their recovery steps (84 %) or side stepping (16 %). Their performance improved over trials, and some participants switched strategies. Angular momenta of the adjusted steps remained small at and following recovery foot landing. Young adults can quickly change foot trajectory after tripping by using different strategies, and without detrimental consequences on balance recovery, in terms of the angular momentum. These results open possibilities for training of tripping reactions. [ABSTRACT FROM AUTHOR]

Abstract: Background: In post-stroke hemiparetic subjects, solid polypropylene ankle-foot-orthoses are commonly prescribed to assist in foot clearance during swing while bracing the ankle during stance. Mobility demands, such as changing walking speed and direction, are accomplished by accelerating or decelerating the body and maintaining dynamic balance. Previous studies have shown that the ankle plantarflexors are primary contributors to these essential biomechanical functions. Thus, with ankle-foot-orthoses limiting ankle motion and plantarflexor output during stance, execution of these walking subtasks may be compromised. This study examined the influence of a solid polypropylene ankle-foot-orthosis on forward propulsion and dynamic balance in healthy adults. Methods: Kinematic and kinetic data were recorded from 10 healthy adults walking with and without a unilateral ankle-foot-orthosis at steady-state slow (0.6m/s) and moderate (1.2m/s) speeds, and during accelerated (0–1.8m/s at 0.06m/s2) and decelerated (1.8–0m/s at −0.06m/s2) walking. Propulsion was quantified by propulsive and braking impulses (i.e., time integral of the anterior–posterior ground reaction force) while dynamic balance was quantified by the peak-to-peak range of whole-body angular momentum. Findings: The propulsive impulses decreased in the leg with ankle-foot-orthosis compared to the contralateral leg and no ankle-foot-orthosis condition. Further, the ankle-foot-orthosis resulted in a greater range of angular momentum in both the frontal and sagittal planes, which were correlated with the reduced peak hip abduction and reduced ankle plantarflexor moments, respectively. Interpretation: Solid ankle-foot-orthoses limit the successful execution of important mobility subtasks in healthy adults and that the prescription of ankle-foot-orthosis should be carefully considered. [Copyright &y& Elsevier]

• A large-scale standardized slip was induced to participants carrying a front load. • Carrying anterior load increases the risk of slip-falls. • The risk of slip-falls is proportional to the weight carried anteriorly. • The poor control of angular momentum causes slip-falls while carrying a front load. Most workplace musculoskeletal injuries result from slip-related falls while carrying a load. Although prior studies inspected the effects of front load carriage on spatiotemporal gait parameters, it remains unclear how the anterior load carriage alters the risk of falls after a slip. This study sought to inspect the impact of anterior load carriage on slip-falls. Thirty young adults were evenly randomized into three groups, each assigned a different anterior load (0%, 10%, or 20% of the bodyweight). Under the protection of a safety harness, all participants were exposed to an unexpected and standardized gait-slip perturbation while walking on a treadmill and carrying the assigned load. Their body's responses to the slip were gathered using a motion capture system. The primary (the slip outcome: fall vs. recovery) and secondary measurements (dynamic gait stability, angular momentum, and downward velocity of the body-load system's center of mass or COM) were determined. The results revealed that an increase in the weight carried raises the rate of falls after a slip. The poor control over the COM's angular momentum and descent, but not dynamic gait stability, were the factors leading to slip-falls during gait for individuals carrying a front load. The findings from this study could shed light on the mechanisms of front load carriage increasing the risk of slip-falls. This can provide preliminary references for designing and assessing safety standards for occupations in which anterior load carriage is necessary to reduce the risk of slip-falls and the resulting injuries. [ABSTRACT FROM AUTHOR]

Abstract: Children with unilateral Cerebral Palsy (CP) have several gait impairments, amongst which impaired gait stability may be one. We tested whether a newly developed stability measure (the foot placement estimator, FPE) which does not require long data series, can be used to asses gait stability in typically developing (TD) children as well as children with CP. In doing so, we tested the FPE''s sensitivity to the assumptions needed to calculate this measure, as well as the ability of the FPE to detect differences in stability between children with CP and TD children, and differences in walking speed. Participants were asked to walk at two different speeds, while gait kinematics were recorded. From these data, the FPE, as well as the error that violations of assumptions of the FPE could have caused were calculated. The results showed that children with CP walked with marked instabilities in anterior–posterior and mediolateral directions. Furthermore, errors caused by violations of assumptions in calculation of FPE were only small (∼1.5cm), while effects of walking speed (∼20cm per m/s increase in walking speed) and group (∼5cm) were much larger. These results suggest that the FPE may be used to quantify gait stability in TD children and children with CP. [Copyright &y& Elsevier]

Abstract: Children with hemiparetic Cerebral Palsy (CP) walk with marked asymmetries. For instance, we have recently shown that they have less arm swing on the affected side, and more arm swing at the unaffected side. Such an increase in arm swing at the unaffected side may be aimed at controlling total body angular momentum about the vertical axis, although it was never investigated in this respect. In the current study, we thus investigated if participants with hemiparetic CP control angular momentum by compensatory movements of the unaffected arm. We measured gait kinematics of 11 CP children, and 24 age matched typically developing (TD) children, walking at both self-selected and fast walking speeds, and calculated angular momenta. We found that children with hemiparetic CP did not have a reduced angular momentum of the affected arm. However, they showed substantial increases in angular momentum generated by the legs, which were compensated by increased angular momentum of the unaffected arm. As a result, there were no differences in total body angular momentum between TD and CP children. Moreover, walking speed had no effect on total body angular momentum in both groups. These findings support the idea that angular momentum during walking is a controlled variable, even in children with hemiplegic CP. [Copyright &y& Elsevier]

Angular momentum is a conserved physical quantity for isolated systems where no external moments act about a body's center of mass (CM). However, in the case of legged locomotion, where the body interacts with the environment (ground reaction forces), there is no a priori reason for this relationship to hold. A key hypothesis in this paper is that angular momentum is highly regulated throughout the walking cycle about all three spatial directions [∣→L(f)∣≈0], and therefore horizontal ground reaction forces and the center of pressure trajectory can be explained predominantly through an analysis that assumes zero net moment about the body's CM. Using a 16-segment human model and gait data for 10 study participants, we found that calculated zero-moment forces closely match experimental values (R²x=0.91; R²y=0.90). Additionally, the centroidal moment pivot (point where a line parallel to the ground reaction force, passing through the CM, intersects the ground) never leaves the ground support base, highlighting how closely the body regulates angular momentum. Principal component analysis was used to examine segmental contributions to whole-body angular momentum. We found that whole-body angular momentum is small, despite substantial segmental momenta, indicating large segment-to-segment cancellations (~95% medio-lateral, ~70% anterior-posterior and ~80% vertical). Specifically, we show that adjacent leg-segment momenta are balanced in the medio-lateral direction (left foot momentum cancels right foot momentum, etc.). Further, pelvis and abdomen momenta are balanced by leg, chest and head momenta in the anterior-posterior direction, and leg momentum is balanced by upper-body momentum in the vertical direction. Finally, we discuss the determinants of gait in the context of these segment-to-segment cancellations of angular momentum. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the effects of various arm swing on postural stability and recovery responses to an unexpected slip during treadmill walking. Fifteen healthy young adults (23.4 ± 2.8 years old) participated in this study. The CAREN-Extended system was used to simulate unexpected slip perturbations in a safe environment while walking symmetrically and asymmetrically with various arm swings (normal, bound, released). Whole-body angular momentum (range), peak trunk angular velocities, step width and stance time were extracted before and after perturbations (when recovering from slip). All participants were able to recover their balance after two strides and no falls occurred. There were significant differences (p < 0.05) in most gait parameters between pre- and post-perturbations. Arm conditions had significant effects on all gait parameters during both pre- and post-perturbation except for stance time. Compared to symmetric walking, walking asymmetrically before a perturbation led to larger step width and stance time among the different arm conditions both before and after the perturbations. Despite the presence of significant effects of different arm and walking conditions on most gait parameters during pre- and post-perturbation, participants were able to implement stabilization strategies to prevent fall even when they were prevented from using their normal arm swing, in both symmetric and asymmetric walking. While our results indicate that perturbations were mild to moderate in magnitude, investigations with elderly and faller populations are needed to examine their susceptibility to these arm and walking conditions when trying to regain postural balance. [ABSTRACT FROM AUTHOR]

Assessment of angular momentum and harmonic ratio for children with cerebral palsy during walking. [ABSTRACT FROM AUTHOR]