Single-leg Support Phase Research Articles

Gait analysis using three-dimensional motion and ground reaction force systems in patients with hemiplegia treated with botulinum toxin type A in ankle plantar flexors.

Objective: The efficacy of botulinum toxin type A (BoNT-A) injection on spasticity has usually been measured using the range of motion (ROM) of joints and Modified Ashworth Scale (MAS); however, they only evaluate muscle tone at rest. We objectively analyzed the gait of three patients with hemiplegia using three-dimensional motion analysis and ground reaction force (GRF) systems to evaluate muscle tone during gait. Materials and Methods: We measured passive ankle dorsiflexion ROM with knee extension and the MAS score for clinical evaluation, and gait speed, stride length, single-leg support phase during the gait cycle, joint angle, joint moment, and GRFs for kinematic evaluation before and one month after BoNT-A injection. Results: All patients showed an increase in ankle dorsiflexion ROM, improvement in MAS score, and increase in stride length. Case 1 showed an increase in gait speed, prolongation of the single-leg support phase, increase in hip extension angle and moment, and improvement in the vertical and anterior-posterior components of the GRFs. Case 2 showed an increase in gait speed, improvement in double knee action, increase in ankle plantar flexion moment, and improvement in propulsion in the progressive component of the GRFs. Case 3 exhibited a laterally directed force in the GRFs. Conclusion: We evaluated the effects of BoNT-A injections in three patients with hemiplegia using three-dimensional motion analysis and GRFs. The results of the gait analysis clarified the improvements and problems in hemiplegic gait and enabled objective explanations for patients.

Biomechanical effects of typical lower limb movements of Chen-style Tai Chi on knee joint.

The load and stress distribution on cartilage and meniscus of the knee joint in typical lower limb movements of Chen-style Tai Chi (TC) and deep squat (DS) were analyzed using finite element (FE) analysis. The loadings for this analysis consisted of muscle forces and ground reaction force (GRF), which were calculated through the inverse dynamic approach based on kinematics and force plate measurements obtained from motion capture experiments. Thirteen experienced practitioners performed four typical TC movements, namely, single whip (SW), brush knee and twist step (BKTS), stretch down (SD), and part the wild horse's mane (PWHM), which exhibit lower posture and greater lower limb force compared to other TC styles. The results indicated that TC required greater lower limb muscle strength than DS, resulting in greater knee joint forces. The stress on the medial cartilage in SW and BKTS fell within a range conductive to maintaining the balance between anabolism and catabolism of cartilage matrix. This was due to the fact that SW and BKTS reduce the medial to total tibiofemoral contact force ratios through knee abduction, which may effectively alleviate mild medial knee osteoarthritis (KOA). However, the greater medial contact force ratios observed in SD and PWHM resulted in great contact stresses that may aggravate the pain of patients with KOA. To mitigate these effects, practitioners should consider elevating their postures appropriately to reduce knee flexion angles, especially during the single-leg support phase. This adjustment can decrease the required muscle strength, load and stress on the knee joint.

Walking performance of persons with chronic stroke changed when looking down but not in dimly lit environment.

It is common to walk under different conditions, such as looking straight head, looking down at the feet or in dimly lit environment. The purpose of this study was to determine the impact of these different conditions on walking performance in persons with and without stroke. This was a case-control study. Persons with chronic unilateral stroke and age-matched control (n = 29 each) underwent visual acuity test, Mini Mental Status Examination (MMSE) and joint position sense test of the knee and ankle. The participants walked at their preferred speed under three walking conditions, looking ahead (AHD), looking down (DWN), and in dimly lit environment (DIM). A motion analysis system was used for the recording of the limb matching test and walking tasks. Stroke participants differed from the control group in MMSE, but not in age, visual acuity or joint position sense. For the control group, the differences between the three walking conditions were nonsignificant. For the stroke group, DWN had significantly slower walking speed, greater step width and shorter single leg support phase, but not different symmetry index or COM location, compared to AHD. The differences between AHD and DIM were nonsignificant. Healthy adults did not change their gait patterns under the different walking conditions. Persons with chronic stroke walked more cautiously but not more symmetrically when looking down at the feet, but not in dimly lit environment. Ambulatory persons with stroke may need to be advised that looking down at the feet while walking could be more challenging.

Generalized Multiphase Dynamic Modeling and Precision Interaction Force Control of a Walking Lower Limb Hydraulic Exoskeleton.

Wearable lower limb hydraulic exoskeletons can be used to augment the human performance in heavy load transportation. Nonlinear and walking phase-dependent dynamics make the lower limb hydraulic exoskeleton become difficult to be modeled. This paper presents a generalized multiphase dynamic modeling method in which the dynamic model of each walking phase can all be solved based on a general higher dimensional dynamic model and different holonomic constraints. Compared to traditional lower limb exoskeleton modeling methods where the modeling of each walking phase is done independently, the proposed method is simple and applicable to arbitrary walking phases, especially for double leg support phase (closed-chain dynamics). Based on the established dynamic models, MIMO adaptive robust cascade force controllers (ARCFC) are designed both for double leg support phase and single leg support phase to effectively address high-order nonlinearities and various modeling uncertainties in hydraulic exoskeletons. An additional torque allocation method is proposed to deal with the overactuated characteristic in double leg support. Comparative simulations are conducted to verify the excellent human-machine interaction force control performance of the proposed scheme.

Influence of dual-tasking on straight ahead and curved walking in older adults

Walking is not an automatic movement task but requires continuous attention resources. While walking and undertaking an additional task (dual tasking), gait changes occur which are associated with falls in older adults. To date, the evaluation of gait characteristics under dual task conditions is typically performed during walking straight ahead (SW); however, everyday life also requires more complex walking maneuvers such as walking in a curve (CW). Complex walking maneuvers may require higher attentional resources and thus might have agreater impact on the gait under dual task conditions. The aim was to compare the gait characteristics under dual task conditions during SW and CW. In 30community-dwelling older adults (mean age: 71.6 ± 6.6years) gait parameters including single leg support phase, velocity, cadence, step length and width were measured by electronic gait analysis (GAITRite®, CIR Systems Inc., Franklin, New Jersey, USA) during SW and CW under single and dual task conditions. For each gait parameter the relative change from single to dual task condition was calculated as dual task costs (DTC) and compared using paired t‑tests. For the single leg support phase, velocity, cadence and step width, descriptive results showed increased DTC during CW (2.08-23.74%) as compared to SW (1.39-12.90%). For cadence (DTC: SW 6.81 ± 12.58%, CW 10.54 ± 13.46%, p = 0.026) and step width (DTC: SW -12.90 ± 18.01%, CW -23.74 ± 56.37%, p = 0.004) the differences were statistically significant. The relative decline in gait performance under dual task conditions is greater during CW than during SW. The results suggest that CW requires greater attentional resources as compared to SW. In turn, the risk of falling might be increased during CW under dual task conditions. The present findings may contribute to the development of new, ecologically valid assessment and training strategies taking complex walking maneuvers into account.

Alterations in over-ground walking patterns in obese and overweight adults

Obesity has been associated with negative effects on postural control, including falls. Previous studies revealed different outcomes regarding the effects of obesity on gait features, and the use of BMI may lead to bias in assessing the true effects of obesity on gait. To better understand the effects of obesity on gait, it is important to examine gait features and associated body composition measures. The purpose of this study was: (1) to assess gait features of normal weight, overweight and obese adults, and (2) to assess the relationship between body composition measures and gait features. Thirty participants were assigned to one of three groups based upon their BMI at the onset of the study: healthy weight (BMI: 18.5–24.9kg/m2), overweight (BMI: 25–29.9kg/m2), or obese (BMI: 30–40kg/m2). Participants performed straight-line over-ground walking through a 200m hallway at their natural preferred speed while wearing their own shoes. The angular displacements, range of motion (ROM), and approximate entropy of kinematic data of the bilateral hips, knees, and ankles in the sagittal plane were computed. Walking speed, step length, stride length, single leg support phase, double leg support phase, swing phase and bilateral stance phase times were extracted from the GaitRite data. Overall, body mass and BMI were associated with peak flexion and ROM in the knees as well as single support, double support, stance, and swing phases. Body fat percentage did not exhibit correlations with measured gait features. Gait variables were more highly correlated with BMI and body mass instead of percent body fat, suggesting that absolute mass is more influential on gait features rather than amount of fat tissue.

A wider pelvis does not increase locomotor cost in humans, with implications for the evolution of childbirth.

The shape of the human female pelvis is thought to reflect an evolutionary trade-off between two competing demands: a pelvis wide enough to permit the birth of large-brained infants, and narrow enough for efficient bipedal locomotion. This trade-off, known as the obstetrical dilemma, is invoked to explain the relative difficulty of human childbirth and differences in locomotor performance between men and women. The basis for the obstetrical dilemma is a standard static biomechanical model that predicts wider pelves in females increase the metabolic cost of locomotion by decreasing the effective mechanical advantage of the hip abductor muscles for pelvic stabilization during the single-leg support phase of walking and running, requiring these muscles to produce more force. Here we experimentally test this model against a more accurate dynamic model of hip abductor mechanics in men and women. The results show that pelvic width does not predict hip abductor mechanics or locomotor cost in either women or men, and that women and men are equally efficient at both walking and running. Since a wider birth canal does not increase a woman’s locomotor cost, and because selection for successful birthing must be strong, other factors affecting maternal pelvic and fetal size should be investigated in order to help explain the prevalence of birth complications caused by a neonate too large to fit through the birth canal.

Validation of visual rating criteria for single leg squat performance in asymptomatic runners

Background: Aberrant neuromuscular control during the single leg support phase of running is thought to contribute to lower limb overuse injuries. The single leg squat (SLSq) is a common clinical test of single leg dynamic control, and demonstrates lower limb kinematics that correlate with jogging kinematics. Criteria for visual rating of SLSq performance are reliable, but have not been validated against gold standard biomechanical measures. This study compared knee valgus torque and lower limb kinematics during SLSq, between runners rated as ‘good’ and ‘poor’ SLSq performers based on visual rating criteria.

Differences of Ballet Turns (Pirouette) Performance Between Experienced and Novice Ballet Dancers

Purpose: This study investigated the different postural control strategies exhibited by experienced and novice dancers in ballet turns (pirouettes). Method: Thirteen novice and 13 experienced dancers performed ballet turns with dominant-leg support. The peak push force was measured in the double-leg support phase. The inclination angles of rotation axis with respect to vertical axis were calculated in the early single-leg support phase as well as the initiation sequence of ankle, knee, and hip joints on the supporting leg. Moreover, the anchoring index of the head was computed in the transverse plane during turning. Results: The novice dancers applied a greater push force, an increased inclination angle of rotation axis, and an insufficient proximal-to-distal extension sequence pattern. The novice dancers also had a smaller head-anchoring index compared with experienced dancers, which meant novice dancers were not using a space target as a stability reference. Conclusions: A poorer performance in novice dancers could result from higher push force in propulsion, lack of a “proximal-to-distal extension sequence” pattern, and lack of visual spotting for postural stability. Training on sequential initiation of lower-extremity joints and rehearsal of visual spotting are essential for novice dancers to obtain better performance on ballet turns.

Turning in a Bipedal Robot

We report the development of turning behavior on a child-size bipedal robot that addresses two common scenarios: turning in place and simultaneous walking and turning. About turning in place, three strategies are investigated and compared, including body-first, leg-first, and body/leg-simultaneous. These three strategies are used for three actions, respectively: when walking follows turning immediately, when space behind the robot is very tight, and when a large turning angle is desired. Concerning simultaneous walking and turning, the linear inverted pendulum is used as the motion model in the single-leg support phase, and the polynomial-based trajectory is used as the motion model in the double-leg support phase and for smooth motion connectivity to motions in a priori and a posteriori single-leg support phases. Compared to the trajectory generation of ordinary walking, that of simultaneous walking and turning introduces only two extra parameters: one for determining new heading direction and the other for smoothing the Center of Mass (COM) trajectory. The trajectory design methodology is validated in both simulation and experimental environments, and successful robot behavior confirms the effectiveness of the strategy.

Effects of leg dominance on performance of ballet turns (pirouettes) by experienced and novice dancers

Turns (pirouettes) are an important movement in ballet and may be affected by “lateral bias”. This study investigated physiological differences exhibited by experienced and novice dancers, respectively, when performing pirouette with dominant and non-dominant leg supports, respectively. Thirteen novice and 13 experienced dancers performed turns on dominant or non-dominant legs. The maximum ankle plantarflexion, knee extension and hip extension were measured during the single-leg support phase. The inclination angle of rotation axis is the angle between instantaneous rotation axis and global vertical axis in the early single-leg support phase. Both groups exhibited a greater hip extension, knee extension, and ankle plantarflexion when performing a turn on the non-dominant leg. For experienced dancers, the inclination angle of rotation axis during the pre-swing phase was generally smaller for dominant leg support than non-dominant leg. However, no significant difference was found in inclination angle of rotation axis of novice dancers. For experienced dancers, an improved performance is obtained when using the dominant leg for support. By contrast, for novice dancers, the performance is independent of choice of support leg. The significant lateral bias in experienced dancers indicates the possible influence of training. That is, repetitive rehearsal on the preferred leg strengthens the impact of side dominance in experienced dancers.

Evaluation of femoral strains with cementless proximal-fill femoral implants of varied stem length

BackgroundThe design intent of proximally-filling lateral flare femoral stems is to load the endosteal surface of the proximal femur both laterally and medially, to achieve normal bone strains. However, the long stem can contact the femoral cortex and may offload the proximal region to some extent. Therefore, in this study, we sought to determine if reducing the stem length, would result in physiologic strain patterns. MethodsUsing the PhotoStress® method we analyzed 13 femurs intact and with three different stem length implants: stemless, ultra-short and short. The test rig loaded the femoral head by simulating the mid-stance single leg support phase of gait with the ilio-tibial band and the hip abductor forces. The strain distribution with each stem length implant was then compared to the intact strain distribution to determine which was most similar. FindingsAs the stem length increased the femurs exhibited a typical pattern of reduced proximal strain and increased distal strain. However, there was some variation in this pattern indicating that the exact stem position and the location of its interaction with the endosteal surface of bone was not the same in each femur. InterpretationThe stemless design provided the best match compared to the native femur and therefore has the greatest potential to address the shortcomings of a stemmed femoral implant. However, the ultra-short implant also exhibited a strain distribution that closely emulated the intact femur, and may represent the best option as there are still several questions pertaining to stability and alignment of a stemless implant.

A Walking Pattern Generator Using a Spherical Inverted Pendulum with an Underfloor Pivot

Humans utilize the configuration with extended knees to achieve efficient walk. A humanoid robot, however, cannot do so, since this posture is a singular configuration. In order to tackle this problem, in our previous work, a walking pattern generator based on the spherical inverted pendulum model has been proposed. It enables to generate up-and-down waist motions and utilizes the singularity neighborhood in the middle of each support phase. However, the spherical inverted pendulum model cannot move the ZMP during each single support phase. In this paper, we propose a new approach to generate a walking pattern based on a Spherical Inverted Pendulum model with an Underfloor Pivot (the SIPUP method). With this method, the ZMP gains mobility during each single-leg support phase, and walking with a smaller acceleration is achieved. In addition, it becomes easy to utilize the singularity neighborhood. As a result, the knee joint can be almost fully extended (less than 0.01 rad). Experimental results show the effectiveness of our approach.

Robust sliding-mode control applied to a 5-link biped robot

In this paper the application of robust control to a 5-link biped robotic model is investigated through the sliding mode approach, and compared to pure computed torque control. The biped consists of five links, namely the torso and two links in each leg. These links are connected via four (two hip and two knee) rotating joints which are considered to be friction-free and driven by independent d.c. motors. The locomotion of the biped is assumed to be constrained on the sagittal plane. The paper provides a full derivation of the biped dynamic model (single-leg support phase, biped-in-the-air phase) and an outline of the computed torque and sliding mode control algorithms. The simulation results were derived with two sets of parameters (one of which corresponds to a human-sized biped) and several degrees of parametric uncertainty (from 10% to 200%). In all cases the results obtained through the sliding mode control were much better than those obtained with the computed torque control. This superiority was shown to become stronger as the degree of uncertainty and the size of the biped increases.

Dynamic Walk of a Biped

The authors have developed five kinds of biped locomotive robots so far. They are named BIPER-1, 2, 3, 4, and 5. All of them are statically unstable but can perform a dynamically stable walk with suitable control. BIPER-1 and BIPER-2 walk only sideways. BIPER-3 is a stilt-type robot whose foot contacts occur at a point and who can walk sideways, back ward, and forward. BIPER-4's legs have the same degrees of freedom as human legs. BIPER-5 is similar to BIPER-3, but in the case of BIPER-5 all apparatus, such as the computer, are mounted on it. This paper deals with the control theory used for BIPER-3 and BIPER-4. In both cases, basically the same control method is applied. The most important point is that the mo tion of either robot during the single-leg support phase can be approximated by the motion of an inverted pendulum. Ac cordingly, in this paper, dynamic walk is considered to be a series of inverted-pendulum motions with appropriate condi tions of connection.