Stance Foot Research Articles

Three single leg standing tests for clinical assessment of chronic plantar heel pain syndrome: static stance, half-squat and heel rise

ObjectiveTo assess reliability and validity of three single leg standing clinical tests in patients with plantar heel pain syndrome (PHPS). DesignCross-sectional reliability study. ParticipantsForty patients diagnosed with PHPS. Main outcome measuresPatients stood on their affected foot in a static stance for up to 30seconds, a half squat for up to 10 repetitions, and a heel rise for up to 10 repetitions. The first sensation of pain (p1) determined the termination of each test, and established a positive test result. The level of p1 was measured using a visual analogue scale (VAS); time or repetitions for each test were recorded. Prior to performing the tests, all patients completed the Foot & Ankle Computerized Adaptive Test to measure functional status (FS). ResultsDetection of p1 in each test showed good reliability for inter- and intrarater assessment (Kappa=0.60 to 0.78 and 0.56 to 0.77, respectively). The intraclass correlation coefficient for the VAS measures was 0.85 to 0.95 for inter-rater assessment and 0.78 to 0.92 for intrarater assessment. However, the Bland and Altman limits of agreement were wide, indicating that these measures were less reliable than the correlation coefficients suggested. Thirty-five patients (88%) experienced a positive pain response to at least one test. Significant correlations were found between the VAS measures in each test and FS (r=0.63 to 0.72). ConclusionsThe static stance, half squat and heel rise tests were easily implemented, and found to be reliable and valid according to one analysis, yet less reliable with another, for pain provocation and VAS levels in patients with PHPS. All three VAS levels correlated well with FS.

Reliability and responsiveness of gait initiation profiles in those with chronic ankle instability

Individuals with chronic ankle instability (CAI) have demonstrated deviations in gait initiation (GI) compared to healthy individuals. However, the intersession reliability of GI measures remains unknown in this population. The objective of this study was to determine the reliability and responsiveness of GI measures between two testing days in those with CAI. Twelve individuals with CAI volunteered. Participants performed barefoot GI on a force plate which captured center of pressure (COP). Data was collected on two separate occasions separated by one week. The GI profile was separated into three phases (S1, S2, and S3). S1 began from the deviation of normal balanced standing to the most posterolateral displacement under the stepping limb. S2 began from the end of S1 to the maximum medial position under the stance foot. S3 began at the end of S2 and continued until the vertical ground reaction force dropped below 100N. COP displacement (cm) was calculated as the sum of resultant vectors of the medial-lateral and anterior-posterior excursions for adjacent COP data points within each phase. The averages of 5 trials were used for analyses. Intraclass correlation coefficients (ICC(2,5)), standard error of measurement, and minimum detectable change (MDC) were calculated to determine reliability and responsiveness. S1, S2, and S3 displacement values were highly reliable between days (ICC(2,5) ≥0.76) with the exception of anterior-posterior S1 and medial-lateral S3. MDC values were relatively small (0.6–2.2cm). GI can be reliably assessed in those with CAI which is important for identifying interventions to alter GI profiles in these individuals.

Anticipatory postural adjustments are unaffected by age and are not absent in patients with the freezing of gait phenomenon

In bipedal gait, the initiation of the first step is preceded by a complex sequence of movements which shift the centre of mass of the body towards the stance foot to allow for a step of the swing foot. These anticipatory postural adjustments (APAs) have been investigated in order to elucidate movement strategies in healthy and diseased persons. We studied the influence of several external parameters (age, type of step initiation) on APAs and investigated whether Parkinsonian patients may have different APAs. As a result, we found that externally elicited steps were preceded by faster and larger APAs than self-timed steps. Parkinsonian patients without the freezing of gait (FOG) phenomenon showed overall slightly reduced APAs but did not clearly differ from patients with FOG. Multiple APAs were seen in up to 25% of the steps of the patients and in a much lower percentage of the steps of control subjects. The results indicate that APAs are significantly influenced by the timing of a step, i.e. are larger in externally elicited steps. The patients showed an overall preserved APA pattern but slowed movements and amplitude, indicating that increased bradykinesia due to progressive illness is a plausible explanation for these findings. The freezing phenomenon is not explained by a general absence or massive reduction in APA measures.

Dynamic stability during running gait termination: Predictors for successful control of forward momentum in children and adults

Reported differences between children and adults with respect to COM horizontal and vertical position to maintain dynamic stability during running deceleration suggest that this relationship may not be as important in children. This study challenged the current dynamic stability paradigm by determining the features of whole body posture that predicted forward velocity and momentum of running gait termination in adults and children. Sixteen adults and 15 children ran as fast as possible and stopped at pre-determined location. Separate regression analyses determined whether COM posterior and vertical positions and functional limb length (distance between COM and stance foot) predicted velocity and momentum for adults and children. COM posterior position was the strongest predictor of forward velocity and momentum in both groups supporting the previously established relationship during slower tasks. COM vertical position also predicted momentum in children, not adults. Higher COM position in children was related to greater momentum; consistent with previously reported differences between children and adults in COM position across running deceleration. COM vertical position was related to momentum but not velocity in children suggesting that strategies used to terminate running may be driven by demands imposed not just by velocity, but also the mass being decelerated.

The influences of foot placement on lumbopelvic rhythm during trunk flexion motion

Different standing postures could potentially influence trunk biomechanics during task performance. The current study investigated how foot placement, especially stance width and foot angle influenced lumbopelvic rhythm during sagittal trunk flexion motion. Ten participants performed pace controlled sagittally symmetric trunk flexion motions while maintaining three different stance widths and two different foot angles. The results showed the narrower stance and angled foot placement conditions generated more in-phase lumbopelvic coordination patterns during trunk flexion motions, possibly due to the reduced base of support and the associated postural stability. Findings of this study provided important information regarding the effects of foot placement on postural control and trunk biomechanics during trunk bending motions; these results suggested that foot placement could alter the motion patterns of spinal segments.

7. Frontal Plane Knee Loading during Bodyweight Squat Performance: Effects of Stance Width and Foot Rotation

The bodyweight squat is routinely used for conditioning of the knee musculature. In the performance of this exercise, modifications in the initial standing position may result in altered frontal plane kneel loading, and hence may potentially be used for targeted exercise prescription. The purpose of this study is to quantify the frontal plane mechanical loading on the knee joint whilst performing the bodyweight squat exercise, and to examine the effects of varying stance width and foot rotation angle. Twenty-four participants (14 males) performed 4 randomized sets of 8 repetitions of the body weight resistant squat exercise in the following conditions: 1) Shoulder width (SW) stance with parallel feet; 2) SW stance with feet externally rotated 30°; 3) 140% SW stance with parallel feet, and; 4) 140% SW stance with the feet externally rotated by 30°. The adduction/abduction knee joint moment experienced across conditions was calculated using inverse dynamics procedures. Moment waveforms were subjected to Principal Component (PC) analysis, with 3 PC’s retained based on a 90% trace criteria. Following, a 1-way repeated measures ANOVA and pair wise comparisons were used to discern differences between conditions. Omnibus test results indicate significant differences across conditions for PC1 and PC2 (p<0.01), Post hoc comparisons and waveform interpretation of PC1 extreme scores showed that the magnitude of the adduction moment was higher throughout the movement in the foot rotated conditions vs. the parallel feet conditions in both stance widths (mean Z scores .69 & .65 vs. -.88 & -.45, p<0.01, respectively). For PC2, significant differences were found between the 2 parallel feet conditions and the 2 foot rotated conditions, as well as between the foot conditions in the wide stance squats. PC2 differences were interpreted as phase shift operators. We found that modification of foot rotation slightly alters the magnitude and timing of knee adduction moment component during performance of the body weight squat. The observed magnitude differences are presumably a consequence of alteration in the location of the point of application of the ground reaction force during the initial standing posture. The findings may assist clinicians in exercise prescription decision making.

Adaptive Robot Biped Locomotion with Dynamic Motion Primitives and Coupled Phase Oscillators

In order to properly function in real-world environments, the gait of a humanoid robot must be able to adapt to new situations as well as to deal with unexpected perturbations. A promising research direction is the modular generation of movements that results from the combination of a set of basic primitives. In this paper, we present a robot control framework that provides adaptive biped locomotion by combining the modulation of dynamic movement primitives (DMPs) with rhythm and phase coordination. The first objective is to explore the use of rhythmic movement primitives for generating biped locomotion from human demonstrations. The second objective is to evaluate how the proposed framework can be used to generalize and adapt the human demonstrations by adjusting a few open control parameters of the learned model. This paper contributes with a particular view into the problem of adaptive locomotion by addressing three aspects that, in the specific context of biped robots, have not received much attention. First, the demonstrations examples are extracted from human gaits in which the human stance foot will be constrained to remain in flat contact with the ground, forcing the "bent-knee" at all times in contrast with the typical straight-legged style. Second, this paper addresses the important concept of generalization from a single demonstration. Third, a clear departure is assumed from the classical control that forces the robot's motion to follow a predefined fixed timing into a more event-based controller. The applicability of the proposed control architecture is demonstrated by numerical simulations, focusing on the adaptation of the robot's gait pattern to irregularities on the ground surface, stepping over obstacles and, at the same time, on the tolerance to external disturbances.

A general relationship links gait mechanics and running ground reaction forces.

The relationship between gait mechanics and running ground reaction forces is widely regarded as complex. This viewpoint has evolved primarily via efforts to explain the rising edge of vertical force-time waveforms observed during slow human running. Existing theoretical models do provide good rising-edge fits, but require more than a dozen input variables to sum the force contributions of four or more vague components of the body's total mass (mb). Here, we hypothesized that the force contributions of two discrete body mass components are sufficient to account for vertical ground reaction force-time waveform patterns in full (stance foot and shank, m1=0.08mb; remaining mass, m2=0.92mb). We tested this hypothesis directly by acquiring simultaneous limb motion and ground reaction force data across a broad range of running speeds (3.0-11.1 m s-1) from 42 subjects who differed in body mass (range: 43-105 kg) and foot-strike mechanics. Predicted waveforms were generated from our two-mass model using body mass and three stride-specific measures: contact time, aerial time and lower limb vertical acceleration during impact. Measured waveforms (N=500) differed in shape and varied by more than twofold in amplitude and duration. Nonetheless, the overall agreement between the 500 measured waveforms and those generated independently by the model approached unity (R2=0.95±0.04, mean±s.d.), with minimal variation across the slow, medium and fast running speeds tested (ΔR2≤0.04), and between rear-foot (R2=0.94±0.04, N=177) versus fore-foot (R2=0.95±0.04, N=323) strike mechanics. We conclude that the motion of two anatomically discrete components of the body's mass is sufficient to explain the vertical ground reaction force-time waveform patterns observed during human running.

Stepping in Place While Voluntarily Turning Around Produces a Long-Lasting Posteffect Consisting in Inadvertent Turning While Stepping Eyes Closed.

Training subjects to step in place on a rotating platform while maintaining a fixed body orientation in space produces a posteffect consisting in inadvertent turning around while stepping in place eyes closed (podokinetic after-rotation, PKAR). We tested the hypothesis that voluntary turning around while stepping in place also produces a posteffect similar to PKAR. Sixteen subjects performed 12 min of voluntary turning while stepping around their vertical axis eyes closed and 12 min of stepping in place eyes open on the center of a platform rotating at 60°/s (pretests). Then, subjects continued stepping in place eyes closed for at least 10 min (posteffect). We recorded the positions of markers fixed to head, shoulder, and feet. The posteffect of voluntary turning shared all features of PKAR. Time decay of angular velocity, stepping cadence, head acceleration, and ratio of angular velocity after to angular velocity before were similar between both protocols. Both postrotations took place inadvertently. The posteffects are possibly dependent on the repeated voluntary contraction of leg and foot intrarotating pelvic muscles that rotate the trunk over the stance foot, a synergy common to both protocols. We propose that stepping in place and voluntary turning can be a scheme ancillary to the rotating platform for training body segment coordination in patients with impairment of turning synergies of various origin.

Hip proprioceptive feedback influences the control of mediolateral stability during human walking.

Active control of the mediolateral location of the feet is an important component of a stable bipedal walking pattern, although the roles of sensory feedback in this process are unclear. In the present experiments, we tested whether hip abductor proprioception influenced the control of mediolateral gait motion. Participants performed a series of quiet standing and treadmill walking trials. In some trials, 80-Hz vibration was applied intermittently over the right gluteus medius (GM) to evoke artificial proprioceptive feedback. During walking, the GM was vibrated during either right leg stance (to elicit a perception that the pelvis was closer mediolaterally to the stance foot) or swing (to elicit a perception that the swing leg was more adducted). Vibration during quiet standing evoked leftward sway in most participants (13 of 16), as expected from its predicted perceptual effects. Across the 13 participants sensitive to vibration, stance phase vibration caused the contralateral leg to be placed significantly closer to the midline (by ∼2 mm) at the end of the ongoing step. In contrast, swing phase vibration caused the vibrated leg to be placed significantly farther mediolaterally from the midline (by ∼2 mm), whereas the pelvis was held closer to the stance foot (by ∼1 mm). The estimated mediolateral margin of stability was thus decreased by stance phase vibration but increased by swing phase vibration. Although the observed effects of vibration were small, they were consistent with humans monitoring hip proprioceptive feedback while walking to maintain stable mediolateral gait motion.

P176. Quantitative analysis of anticipatory postural adjustment in patients with Parkinson’s disease

Background Step initiation is considered to be one of the central human balance networks, and is a complex movement. Deficits can lead to balance disturbances with consecutive falls and injuries, and often occur in Parkinson’s disease (PD), where they are associated with akinetic-rigid subtype, freezing and falls. PD can therefore be seen as a model disorder for studying step initiation deficits. The movement consists basically of an initial lateral movement of the hip over the stance foot (anticipatory postural adjustment, APA; this is the most relevant part), and a consecutive release of the swing leg for performance of the first step. Despite the relevance of this movement deficit, little is known about (i) characteristic parameters of APA associated with PD subtypes, and (ii) the influence of dopaminergic treatment on APA. Methods APA was repeatedly assessed with a standardized protocol after a 30 s standing phase in 120 PD patients during their medication off state. Sixty of them underwent the identical assessment also during on medication. Before the assessment, participants were equipped with wearable 6 sensors (Mobility Lab®, APDM, Oregon). The following parameters were extracted from the APA movement: amplitude in anterioposterior (AP) direction (AP), amplitude in mediolateral (ML) direction, time-to-peak AP, time-to-peak ML, total duration and mean velocity. Demographic and clinical data were collected based on questionnaires and surveys (e.g., with the Unified Parkinson’s disease Rating scale, Mini Mental Status Examination, Montreal Cognitive Assessment and the Becks Depressions Inventory). Results Preliminary analyses revealed that total duration and mean velocity of APA did not significantly differ between PD subtypes (tremor-dominant versus akinetic-rigid). However, amplitude in ML direction was significantly lower in the akinetic-rigid subtype, compared to tremor-dominant PD patients. Medication status did not influence any of the above-mentioned APA parameters significantly. Conclusion This study on a large cohort shows that trunk acceleration in mediolateral direction is probably the most relevant parameter for proper APA performance in PD patients, and that dopaminergic medication does obviously not have a relevant influence on the movement. As APA is associated with severe symptoms and events of PD such as freezing, falls and injuries, non-medical treatment of PD patients should address potential APA deficits, and train them specifically.

P57. Validation of gait analysis with inertial sensors

Inertial sensors are electric circuits which measure acceleration and rotational velocity. This information is needed to determine the 3-D position of a body in space. With the help of those sensors gait can be recorded. The method was validated by a motion-capture system. We examined twelve healthy young men. Sensors were attached at the thigh as well as at the lower leg on each side. One sensor consisted of one gyroscope and two accelerometers. With the help of an integrated Kalman Filter it was possible to calculate the position of all 4 leg segments in the sagittal plane. Specific pattern of gyroscopic and accelerometric data helped defining moments of terminal contact (toe-off) and initial contact (heel strike). These events were validated by a pressure-sensitive inserted sole. To reconstruct the position of the swing foot, forward kinematics were used, i.e. the stance foot was taken a pivotal point and the position of the leg segments was computed with reference to that point so it was possible to calculate step length and step velocity. We compared this data with data synchronously obtained from a motion capture system while subjects walked on a treadmill. Comparison of the time of initial and terminal contact obtained by inertial sensors and pressure sensitive soles resulted in very small deviations within the range of data resolution. Correlation between segment angles measured with inertial sensors and motion capture system was above r = 0.9. Correlation between step length measured by these two systems was above r > 0.8 and could be increased by a calibration of the inertial-sensors system by a defined gait distance. Gait analysis with inertial sensors is less expensive than with conventional methods and allows for the assessment of gait in more natural environments. The actual disadvantage of less precision is compensated in future with better sensors and software.

Coupling mechanical design and control design for energy-efficient and stable walking of a compass-like biped

This paper aims at developing a highly efficient walking scheme for compass-like biped robots with feet. Towards this goal, a latch attached to the hip is introduced to lock the hip joint when the hip joint retracts to the desired value and spring devices are installed in the ankle joints to reduce the inputs of the ankles. Moreover, the stance foot allowed to rotate about the toe is considered. With these setups, a highly efficient limit-cycle walking gait is obtained by using the method of Poincaré shooting with the objective of minimizing the dimensionless specific mechanical cost of transport. However, this limit-cycle walking gait is unstable. To stabilize it, a new control strategy is proposed based on transverse coordinate linearization on moving Poincaré sections. A series of numerical simulations show that such a robot model under the proposed control law can walk stably and efficiently.

Gender difference in older adult’s utilization of gravitational and ground reaction force in regulation of angular momentum during stair descent

Angular momentum of the body is a highly controlled quantity signifying stability, therefore, it is essential to understand its regulation during stair descent. The purpose of this study was to investigate how older adults use gravity and ground reaction force to regulate the angular momentum of the body during stair descent. A total of 28 participants (12 male and 16 female; 68.5years and 69.0years of mean age respectively) performed stair descent from a level walk in a step-over-step manner at a self-selected speed over a custom made three-step staircase with embedded force plates. Kinematic and force data were used to calculate angular momentum, gravitational moment, and ground reaction force moment about the stance foot center of pressure. Women show a significantly greater change in normalized angular momentum (0.92Nms/Kgm; p=.004) as compared to men (0.45Nms/Kgm). Women produce higher normalized GRF (p=.031) during the double support phase. The angular momentum changes show largest backward regulation for Step 0 and forward regulation for Step 2. This greater difference in overall change in the angular momentum in women may explain their increased risk of fall over the stairs.

Effects of neuromuscular fatigue on perceptual-cognitive skills between genders in the contribution to the knee joint loading during side-stepping tasks

This study investigated whether neuromuscular fatigue affects the neuromuscular control of an athlete within a sports context setting and whether these effects were more pronounced in the females. Lower limb joint kinetics of 6 male and 6 female inter-varsity soccer players performing side-stepping tasks in non-fatigue versus fatigue and anticipated versus unanticipated conditions were quantified using 10 Motion Analysis Corporation cameras and a Kistler™ force platform. The Yo-Yo intermittent recovery Level 1 fatigue protocol was employed. Stance foot initial contact and peak forces, and peak joint knee moments of the lower limb were submitted to a 3-way mixed-model repeated measure ANOVA. The results suggested that males tend to elicit significantly higher knee joint loadings when fatigued. In addition, males elicited significantly higher peak proximal tibia anterior/posterior shear force, vertical ground reaction force at initial contact and peak internal rotational moments than females. These findings suggested that males were at greater overall injury risk than females, especially in the sagittal plane. Neuromuscular control-based training programmes/interventions that are designed to reduce the risk of the non-contact ACL injury need to be customised for the different genders.

Zero-Moment Point-Based Biped Robot with Different Walking Patterns

Abstract —This paper addresses three issues of motion planning for zero-moment point (ZMP)-based biped robots. First, three methods have been compared for smooth transition of biped locomotion from the single support phase (SSP) to the double support phase (DSP) and vice versa. All these methods depend on linear pendulum mode (LPM) to predict the trajectory of the center of gravity (COG) of the biped. It has been found that the three methods could give the same motion of the COG for the biped. The second issue is investigation of the foot trajectory with different walking patterns especially during the DSP. The characteristics of foot rotation can improve the stability performance with uniform configurations. Last, a simple algorithm has been proposed to compensate for ZMP deviations due to approximate model of the LPM. The results show that keeping the stance foot flat at beginning of the DSP is necessary for balancing the biped robot. Index Terms —Biped robot, Zero-moment point, Walking pattern generators, Gait cycle, Single support phase, Double support phase.

A Simple Algorithm for Generating Stable Biped Walking Patterns

paper proposes a thorough algorithm that can tune the walking parameters (hip height, distance traveled by the hip, and times of single support phase SSP and double support phase DSP) to satisfy the kinematic and dynamic constraints: singularity condition at the knee joint, zero-moment point (ZMP) constraint, and unilateral contact constraints. Two walking patterns of biped locomotion have been investigated using the proposed algorithm. The distinction of these walking patterns is that the stance foot will stay fixed during the first sub-phase of the DSP for pattern 1, while it will rotate simultaneously at beginning of the DSP for pattern 2. A seven-link biped robot is simulated with the proposed algorithm. The results show that the proposed algorithm can compensate for the deviation of the ZMP trajectory due to approximate model of the pendulum model; thus balanced motion could be generated. In addition, it is shown that keeping the stance foot fixed during the first sub-phase of the DSP is necessary to evade deviation of ZMP from its desired trajectory resulting in unbalanced motion; thus, walking pattern 1 is preferred practically.

Stepping in the direction of the fall: the next foot placement can be predicted from current upper body state in steady-state walking.

During human walking, perturbations to the upper body can be partly corrected by placing the foot appropriately on the next step. Here, we infer aspects of such foot placement dynamics using step-to-step variability over hundreds of steps of steady-state walking data. In particular, we infer dependence of the 'next' foot position on upper body state at different phases during the 'current' step. We show that a linear function of the hip position and velocity state (approximating the body center of mass state) during mid-stance explains over 80% of the next lateral foot position variance, consistent with (but not proving) lateral stabilization using foot placement. This linear function implies that a rightward pelvic deviation during a left stance results in a larger step width and smaller step length than average on the next foot placement. The absolute position on the treadmill does not add significant information about the next foot relative to current stance foot over that already available in the pelvis position and velocity. Such walking dynamics inference with steady-state data may allow diagnostics of stability and inform biomimetic exoskeleton or robot design.

Balance control of planar biped robots using virtual holonomic constraints

SUMMARYThe balance control problem of planar bipedal robots during disturbed standing is investigated. Virtual holonomic constraints which specify the angles of actuated joints as a function of the rotation angle between the sole of the stance foot and the ground are recalled. These constraints enable the robot to avoid turnover during external disturbances similar to how a human being would react. Moreover, for a disturbance beyond the balance conditions for single-leg support, the robot changes to a double support posture to avoid turnover by the virtual holonomic constraints. Further, for a special kind of balance: standing on toe which leads to underactuation, we also give the design conditions of the virtual holonomic constraints.

Impact on the biomechanics of overground gait of using an ‘Echelon’ hydraulic ankle–foot device in unilateral trans-tibial and trans-femoral amputees

BackgroundIf a prosthetic foot creates resistance to forwards shank rotation as it deforms during loading, it will exert a braking effect on centre of mass progression. The present study determines whether the centre of mass braking effect exerted by an amputee's habitual rigid ‘ankle’ foot was reduced when they switched to using an ‘Echelon’ hydraulic ankle–foot device. MethodsNineteen lower limb amputees (eight trans-femoral, eleven trans-tibial) walked overground using their habitual dynamic-response foot with rigid ‘ankle’ or ‘Echelon’ hydraulic ankle–foot device. Analysis determined changes in how the centre of mass was transferred onto and above the prosthetic-foot, freely chosen walking speed, and spatio-temporal parameters of gait. FindingsWhen using the hydraulic device both groups had a smoother/more rapid progression of the centre of pressure beneath the prosthetic hindfoot (p≤0.001), and a smaller reduction in centre of mass velocity during prosthetic-stance (p<0.001). As a result freely chosen walking speed was higher in both groups when using the device (p≤0.005). In both groups stance and swing times and cadence were unaffected by foot condition whereas step length tended (p<0.07) to increase bilaterally when using the hydraulic device. Effect size differences between foot types were comparable across groups. InterpretationUse of a hydraulic ankle–foot device reduced the foot's braking effect for both amputee groups. Findings suggest that attenuation of the braking effect from the foot in early stance may be more important to prosthetic-foot function than its ability to return energy in late stance.