Control of lateral weight transfer is associated with walking speed in individuals post-stroke

Restoring functional gait speed is an important goal for rehabilitation post-stroke. During walking, transferring of one’s body weight between the limbs and maintaining balance stability are necessary for independent functional gait. Although it is documented that individuals post-stroke commonly have difficulties with performing weight transfer onto their paretic limbs, it remains to be determined if these deficits contributed to slower walking speeds. The primary purpose of this study was to compare the weight transfer characteristics between slow and fast post-stroke ambulators. Participants (N = 36) with chronic post-stroke hemiparesis walked at their comfortable and maximal walking speeds on a treadmill. Participants were stratified into 2 groups based on their comfortable walking speeds (≥0.8 m/s or <0.8 m/s). Minimum body center of mass (COM) to center of pressure (COP) distance, weight transfer timing, step width, lateral foot placement relative to the COM, hip moment, peak vertical and anterior ground reaction forces, and changes in walking speed were analyzed. Results showed that slow walkers walked with a delayed and deficient weight transfer to the paretic limb, lower hip abductor moment, and more lateral paretic limb foot placement relative to the COM compared to fast walkers. In addition, propulsive force and walking speed capacity was related to lateral weight transfer ability. These findings demonstrated that deficits in lateral weight transfer and stability could potentially be one of the limiting factors underlying comfortable walking speeds and a determinant of chronic stroke survivors’ ability to increase walking speed.     

Influence of gait speed on the control of mediolateral dynamic stability during gait initiation

This study investigated the influence of gait speed on the control of mediolateral dynamic stability during gait initiation. Thirteen healthy young adults initiated gait at three self-selected speeds: Slow, Normal and Fast. The results indicated that the duration of anticipatory postural adjustments (APA) decreased from Slow to Fast, i.e. the time allocated to propel the centre of mass (COM) towards the stance-leg side was shortened. Likely as an attempt at compensation, the peak of the anticipatory centre of pressure (COP) shift increased. However, COP compensation was not fully efficient since the results indicated that the mediolateral COM shift towards the stance-leg side at swing foot-off decreased with gait speed. Consequently, the COM shift towards the swing-leg side at swing heel-contact increased from Slow to Fast, indicating that the mediolateral COM fall during step execution increased as gait speed rose. However, this increased COM fall was compensated by greater step width so that the margin of stability (the distance between the base-of-support boundary and the mediolateral component of the “extrapolated centre of mass”) at heel-contact remained unchanged across the speed conditions. Furthermore, a positive correlation between the mediolateral extrapolated COM position at heel-contact and step width was found, indicating that the greater the mediolateral COM fall, the greater the step width. Globally, these results suggest that mediolateral APA and step width are modulated with gait speed so as to maintain equivalent mediolateral dynamical stability at the time of swing heel-contact.     

Dynamic stability of superior vs. inferior body segments in individuals with transtibial amputation walking in destabilizing environments

Interestingly, young and highly active people with lower limb amputation appear to maintain a similar trunk and upper body stability during walking as able-bodied individuals. Understanding the mechanisms underlying how this stability is achieved after lower-leg amputation is important to improve training regimens for improving walking function in these patients. This study quantified how superior (i.e., head, trunk, and pelvis) and inferior (i.e., thigh, shank, and feet) segments of the body respond to continuous visual or mechanical perturbations during walking. Nine persons with transtibial amputation (TTA) and 12 able-bodied controls (AB) walked on a 2 m×3 m treadmill in a Computer Assisted Rehabilitation Environment (CAREN). Subjects were perturbed by continuous pseudo-random mediolateral movements of either the treadmill platform or the visual scene. TTA maintained a similar local and orbital stability in their superior body segments as AB throughout both perturbation types. However, for their inferior body segments, TTA subjects exhibited greater dynamic instability during perturbed walking. In TTA subjects, these increases in instability were even more pronounced in their prosthetic limb compared to their intact leg. These findings demonstrate that persons with unilateral lower leg amputation maintain upper body stability in spite of increased dynamic instability in their impaired lower leg. Thus, transtibial amputation does significantly impair sensorimotor function, leading to substantially altered dynamic movements of their lower limb segments. However, otherwise relatively healthy patients with unilateral transtibial amputation appear to retain sufficient remaining sensorimotor function in their proximal and contralateral limbs to adequately compensate for their impairment.     

Local dynamic stability of treadmill walking: Intrasession and week-to-week repeatability

Repetitive falls degrade the quality of life of elderly people and of patients suffering of various neurological disorders. In order to prevent falls while walking, one should rely on relevant early indicators of impaired dynamic balance. The local dynamic stability (LDS) represents the sensitivity of gait to small perturbations: divergence exponents (maximal Lyapunov exponents) assess how fast a dynamical system diverges from neighbor points. Although numerous findings attest the validity of LDS as a fall risk index, reliability results are still sparse. The present study explores the intrasession and intersession repeatability of gait LDS using intraclass correlation coefficients (ICC) and standard error of measurement (SEM). Ninety-five healthy individuals performed 5 min treadmill walking in two sessions separated by 9 days. Trunk acceleration was measured with a 3D accelerometer. Three time scales were used to estimate LDS: over 4–10 strides (λ_4–10), over one stride (λ₁) and over one step (λ_0.5). The intrasession repeatability was assessed from three repetitions of either 35 strides or 70 strides taken within the 5 min tests. The intersession repeatability compared the two sessions, which totalized 210 strides. The intrasession ICCs (70-strides estimates/35-strides estimates) were 0.52/0.18 for λ_4–10 and 0.84/0.77 for λ₁ and λ_0.5. The intersession ICCs were around 0.60. The SEM results revealed that λ_0.5 measured in medio-lateral direction exhibited the best reliability, sufficient to detect moderate changes at individual level (20%). However, due to the low intersession repeatability, one should average several measurements taken on different days in order to better approximate the true LDS.     

Age-related mechanical work expenditure during normal walking: The Baltimore Longitudinal Study of Aging

The aim of this cross-sectional study was to delineate age-associated kinematic and kinetic gait patterns of normal walking, and to test the hypothesis that older adults exhibit gait patterns that reduce generative mechanical work expenditures (MWEs). We studied 52 adult Baltimore Longitudinal Study of Aging participants (means age 72±9, from 60 to 92 years) who could walk 4 m unaided. Three-dimensional kinematic and kinetic parameters assessed during rotation-defined gait periods were used to estimate MWEs for the rotation of lower extremities about the medial–lateral (ML) and anterior–posterior (AP) axes of proximal joints, which represent MWEs in the AP and ML sides, respectively. Relationships between gait parameters and age were examined using regression analysis with adjustments for walking speed, sex, height, and weight. Older age was associated with slower self-selected walking speed (p<0.001), shorter stride length (p<0.001), and greater propensity of landing flat-footed (p=0.003). With older age, hip generative MWE for thigh rotation was lower about the AP axis (hip abduction and adduction) during stance (p=0.010) and higher about the ML axis (hip extension and flexion) during late stance (p<0.001). Knee absorptive MWE for shank rotation about the AP axis (knee abduction and adduction) during early stance was also lower with older age (p<0.003). These age-related gait patterns may represent a compensatory effort to maintain balance and may also reflect mobility limitations.     

Walking at the preferred stride frequency maximizes local dynamic stability of knee motion

Healthy humans display a preference for walking at a stride frequency dependent on the inertial properties of their legs. Walking at preferred stride frequency (PSF) is predicted to maximize local dynamic stability, whereby sensitivity to intrinsic perturbations arising from natural variability inherent in biological motion is minimized. Previous studies testing this prediction have employed different variability measures, but none have directly quantified local dynamic stability by computing maximum finite-time Lyapunov exponent (λ^Max), which quantifies the rate of divergence of nearby trajectories in state space. Here, ten healthy adults walked 45 m overground while sagittal motion of both knees was recorded via electrogoniometers. An auditory metronome prescribed 7 different frequencies relative to each individual's PSF (PSF; ±5, ±10, ±15 strides/min). Stride frequencies were performed under both freely adopted speed (FS) and controlled speed (CS: set at the speed of PSF trials) conditions. Local dynamic stability was maximal (λ^Max was minimal) at the PSF, becoming less stable for higher and lower stride frequencies. This occurred under both FS and CS conditions, although controlling speed further reduced local dynamic stability at non-preferred stride frequencies. In contrast, measures of variability revealed effects of stride frequency and speed conditions that were distinct from λ^Max. In particular, movement regularity computed by approximate entropy (ApEn) increased for slower walking speeds, appearing to depend on speed rather than stride frequency. The cadence freely adopted by humans has the benefit of maximizing local dynamic stability, which can be interpreted as humans tuning to their resonant frequency of walking.     

The effects of sensory loss and walking speed on the orbital dynamic stability of human walking

Peripheral sensory feedback is believed to contribute significantly to maintaining walking stability. Patients with diabetic peripheral neuropathy have a greatly increased risk of falling. Previously, we demonstrated that slower walking speeds in neuropathic patients lead to improved local dynamic stability. However, all subjects exhibited significant local instability during walking, even though no subject fell or stumbled during testing. The present study was conducted to determine if and how significant changes in peripheral sensation and walking speed affect orbital stability during walking. Trunk and lower extremity kinematics were examined from two prior experiments that compared patients with significant neuropathy to healthy controls and walking at multiple different speeds in young healthy subjects. Maximum Floquet multipliers were computed for each time series to quantify the orbital stability of these movements. All subjects exhibited orbitally stable walking kinematics, even though these same kinematics were previously shown to be locally unstable. Differences in orbital stability between neuropathic and control subjects were small and, with the exception of knee joint movements (p=0.001), not statistically significant (0.380p0.946). Differences in knee orbital stability were not mediated by differences in walking speed. This was supported by our finding that although orbital stability improved slightly with slower walking speeds, the correlations between walking speed and orbital stability were generally weak (r(2)16.7%). Thus, neuropathic patients do not gain improved orbital stability as a result of slowing down and do not experience any loss of orbital stability because of their sensory deficits.     

Effects of aging and arm swing on the metabolic cost of stability in human walking

To gain insight into the mechanical determinants of walking energetics, we investigated the effects of aging and arm swing on the metabolic cost of stabilization. We tested two hypotheses: (1) elderly adults consume more metabolic energy during walking than young adults because they consume more metabolic energy for lateral stabilization, and (2) arm swing reduces the metabolic cost of stabilization during walking in young and elderly adults. To test these hypotheses, we provided external lateral stabilization by applying bilateral forces (10% body weight) to a waist belt via elastic cords while young and elderly subjects walked at 1.3m/s on a motorized treadmill with arm swing and with no arm swing. We found that the external stabilizer reduced the net rate of metabolic energy consumption to a similar extent in elderly and young subjects. This reduction was greater (6-7%) when subjects walked with no arm swing than when they walked normally (3-4%). When young or elderly subjects eliminated arm swing while walking with no external stabilization, net metabolic power increased by 5-6%. We conclude that the greater metabolic cost of walking in elderly adults is not caused by a greater cost of lateral stabilization. Moreover, arm swing reduces the metabolic cost of walking in both young and elderly adults likely by contributing to stability.     

Stabilizing effect of polyols is sensitive to inherent stability of protein

In studies on polyol-mediated protein stabilization, the polyols are the preferred variable and less importance is given to the intrinsic properties of the protein used. We investigated the stabilizing effects of glycerol on three in vitro evolved lipase mutants with varying stabilities and also in a broad pH range of 3.3-12.1. Significant linear negative correlation between increment in stability due to glycerol and prior stability suggests that stabilizing effects of glycerol depend on the prior stability of the protein. Polar/nonpolar surface area and charge do not have a bearing on the stabilizing effects of glycerol.     

Computational evaluation of load carriage effects on gait balance stability

Evaluating the effects of load carriage on gait balance stability is important in various applications. However, their quantification has not been rigorously addressed in the current literature, partially due to the lack of relevant computational indices. The novel Dynamic Gait Measure (DGM) characterizes gait balance stability by quantifying the relative effects of inertia in terms of zero-moment point, ground projection of center of mass, and time-varying foot support region. In this study, the DGM is formulated in terms of the gait parameters that explicitly reflect the gait strategy of a given walking pattern and is used for computational evaluation of the distinct balance stability of loaded walking. The observed gait adaptations caused by load carriage (decreased single support duration, inertia effects, and step length) result in decreased DGM values (p < 0.0001), which indicate that loaded walking motions are more statically stable compared with the unloaded normal walking. Comparison of the DGM with other common gait stability indices (the maximum Floquet multiplier and the margin of stability) validates the unique characterization capability of the DGM, which is consistently informative of the presence of the added load.     

The effect of resistance level and stability demands on recruitment patterns and internal loading of spine in dynamic flexion and extension using a simple trunk model

The effects of external resistance on the recruitment of trunk muscles in sagittal movements and the coactivation mechanism to maintain spinal stability were investigated using a simple computational model of iso-resistive spine sagittal movements. Neural excitation of muscles was attained based on inverse dynamics approach along with a stability-based optimisation. The trunk flexion and extension movements between 60° flexion and the upright posture against various resistance levels were simulated. Incorporation of the stability constraint in the optimisation algorithm required higher antagonistic activities for all resistance levels mostly close to the upright position. Extension movements showed higher coactivation with higher resistance, whereas flexion movements demonstrated lower coactivation indicating a greater stability demand in backward extension movements against higher resistance at the neighbourhood of the upright posture. Optimal extension profiles based on minimum jerk, work and power had distinct kinematics profiles which led to recruitment patterns with different timing and amplitude of activation.     

The effect of uphill stride manipulation on race walking gait

Stride length analysis represents an easy method for assessing race walking kinematics. However, the stride parameters emerging from such an analysis have never been used to design a training protocol aimed at increasing stride length. With this aim, we investigated the effects of stride frequency manipulation during three weeks of uphill (2%) training on stride length at iso-efficiency speed. Twelve male race walkers were randomly allocated to one of two training groups: stride frequency manipulation (RWM, n=6) and free stride frequency (RWF, n=6). Results. Kinematic parameters measured before and after the 3-week training in RWM showed increased stride length (4.54%; p<0.0001) and contact time (4.58%; p<0.001); inversely, a decreased stride frequency (4.44%; p<0.0001) and internal work (7.09%; p<0.05) were found. In RWF the effect of the training showed a decrease in stride length (1.18%; p<0.0001) and contact time (<1%; p<0.0001) with respect to baseline conditions and an increased stride frequency and internal work of 1.19% (p<0.0001). These results suggest that using slopes (2%) as RWM could help coaches to provide some training methods that would improve an athlete''s performance, through increasing stride length without altering his or her race walking technique or metabolic demands.     

乳杆菌活菌制剂对细菌性阴道病局部免疫的调节

目的检测正常人和细菌性阴道病(BV)患者治疗前后阴道局部细胞因子的变化,探讨乳杆菌活菌制剂对女性生殖道免疫的影响,为阴道微生态平衡与阴道黏膜免疫屏障的关系的研究提供一定的依据。方法用乳杆菌活菌制剂治疗BV,通过酶联免疫吸附试验法即ELISA法来检测BV患者治疗前后及正常健康妇女阴道局部细胞因子sIgA、IL-2、IL-13的水平。结果 sIgA、IL-13水平治疗前组较对照组明显升高(P<0.01),治疗后组较治疗前组水平下降(P<0.05),治疗后组较对照组水平升高(P>0.05);IL-2水平治疗前组较对照组明显降低,治疗后组较治疗前组明显升高(P<0.05),治疗后组较对照组下降(P<0.05)。结论 BV患者阴道局部免疫功能发生了改变;乳杆菌活菌制剂对BV患者阴道局部免疫具调节作用.     

The effect of environmental stability on hyporheic community structure

Interstitial water samples were collected from two well depths (30 and 60 cm) from 8 rivers in the Cass-Craigieburn region, South Island (New Zealand) during January 1998 to assess the hyporheos in streams of differing stability. Hyporheic water chemistry was more similar to surface water chemistry at unstable sites than at stable sites. The greatest diversity of both epigean and hypogean animals occurred at intermediate levels of disturbance; however, invertebrate density declined with increasing bed movement. Abundance of epigean animals also increased with declining environmental stability (i.e., increasing bed movement). Water chemistry was most like the river channel at unstable sites, probably because less stable substrates had increased interstitial flow facilitating a greater supply of water from the surface channel. In contrast, stable sites were spring fed and groundwater had a greater influence. Thus, substrate stability may influence hyporheic water chemistry and porosity by changing the interaction between ground and surface waters. Epigean taxa may be less abundant at stable sites because the chemical nature of the water is least like the river channel (e.g. low dissolved oxygen, higher temperature and higher conductivity), while the abundance of hypogean animals is greater, as these taxa are more tolerant of this water chemistry, and are thus capable of persisting in the stable substrates.     

The effect of methyl-β-cyclodextrin on the stability of Bordetella pertussis filamentous haemagglutinin

Abstract It has been demonstrated that filamentous haemagglutinin (FHA) purified from Bordetella pertussis is stable on static incubation but is unstable and quickly loses HA activity when incubated with shaking. Methylβcyclodextrin (CD) was found to have a concentration-dependent stabilizing effect on FHA incubated with shaking, suggesting that the ability of CD to enhance yields of FHA in shaken cultures could be wholly or partly due to a stabilizing effect of CD on FHA. However, only weak binding of CD to FHA was demonstrated by an ultrafiltration micropartition method and binding of CD to B. pertussis cells was not related to the presence or absence of FHA on the cell surface.     

The effect of autoclaving on the dispersibility and stability of three neutral polysaccharides in dilute aqueous solutions

The dispersibility of three neutral polysaccharides, oat β-glucan, detarium xyloglucan and dextran in a dilute water–cadoxen mixture was studied by viscosity measurement. It was found that intrinsic viscosity measurement, with water–cadoxen mixtures as solvents, is a useful tool to distinguish polymer degradation from disruption of supramolecular aggregates. This approach, in conjunction with size exclusion chromatography, was used to study the effects of heat and pressure treatment on the dispersibility and stability of three polysaccharides in aqueous solutions. Autoclaving treatment at 121°C for 15 min may reduce the degree of aggregation. Following autoclaving in aqueous solution, the Huggins constants decreased from 0.66 to 0.42 for oat β-glucan and from 0.63 to 0.56 for detarium xyloglucan. It remains the same for dextran, indicating good solubility of this polymer in water. The current treatment did not cause evident changes in molecular weight and structures to detarium xyloglucan and dextran. However, degradation occurred with oat β-glucan. The Burchard–Stockmayer–Fixman approach was applied to estimate the unperturbed dimension of oat β-glucan and detarium xyloglucan on samples after autoclaving. The characteristic ratio C_∞ was found to be 7.3 for detarium xyloglucan and 4.7 for oat β-glucan, corresponding to the Kratky–Porod persistence lengths of 2.0 and 1.2 nm, respectively.     

The effect of dynamic light regimes on Chlorella

The patterns of diurnal variations in pigmentation and optical cross-section were compared for two cyclostat cultures of Chlorella pyrenoidosa, where the dynamics of the photoperiod differed. Populations were light-limited, nutrient rich and growing on an 8:16 light-dark (LD) cycle. One light regime was an 8 h sine function of the light period (sinusoidal culture), while the second had an 1 h sine function super-imposed on the 8 hour sine function (oscillating sinusoidal culture). Hourly samples were taken throughout a 12 h period including the light period. Determinations were made of chlorophyll (Chl) a and b abundance, in vivo absorption spectra, cell number and volume and used to derive both cell-specific (cell) and optical chlorophyll specific (chl) cross sections, as well as the absorption efficiency, Q, of the cells. The results indicate that C. pyrenoidosa is capable of adapting to dynamics in light intensity within an 8 h photoperiod. The sinusoidal culture showed a constant decrease in the Chl a/b ratio of 28% while the total Chl content per cell increased slightly and chl and Q remained constant, suggesting coordinated changes in reaction centers and light harvesting complexes. Over the oscillating photoperiod, however, the second culture displayed a diurnal variation in Chl a/b ratio, a 20% increase in chl and an apparent oscillation in Q. These observations suggest that an oscillating photoperiod promoted the capability of Chl molecules to collect light and that the fractional area of all Chl molecules exposed to the photon flux is inversely related to the photon flux.     

The effect of textured surfaces on postural stability and lower limb muscle activity

Textured insoles may enhance sensory input on the plantar surfaces of the feet, thereby influencing neuromuscular function. The aim of this study was to investigate whether textured surfaces alter postural stability and lower limb muscle activity during quiet bipedal standing balance with eyes open. Anterior–posterior (AP) and mediolateral (ML) sway variables and the intensity of electromyographic (EMG) activity in eight dominant lower limb muscles were collected synchronously over 30 s in 24 young adults under three randomised conditions: control surface (C), texture 1 (T1) and texture 2 (T2). Repeated measures ANOVA showed that the textured surfaces did not significantly affect AP or ML postural sway in comparison to the control condition (p > 0.05). Neither did the textured surfaces significantly alter EMG activity in the lower limbs (p > 0.05). Under the specific conditions of this study, texture did not affect either postural sway or lower limb muscle activity in static bipedal standing. The results of this study point to three areas of further work including the effect of textured surfaces on postural stability and lower limb muscle activity: (i) in young healthy adults under more vigorous dynamic balance tests, (ii) post-fatigue, and (iii) in older adults presenting age-related deterioration.     

The effect of some osmolytes on the activity and stability of mushroom tyrosinase

The thermodynamical stability and remained activity of mushroom tyrosinase (MT) fromAgaricus bisporus in 10 mM phosphate buffer, pH 6.8, stored at two temperatures of 4 and 40°C were investigated in the presence of three different amino acids (His, Phe and Asp) and also trehalose as osmolytes, for comparing with the results obtained in the absence of any additive. Kinetics of inactivation obeye the first order law. Inactivation rate constant (k_inact) value is the best parameter describing effect of osmolytes on kinetic stability of the enzyme. Trehalose and His have the smallest value of k_inact(0.7×10⁻⁴s⁻¹) in comparison with their absence (2.5×10⁻⁴s⁻¹). Moreover, to obtain effect of these four osmolytes on thermodynamical stability of the enzyme, protein denaturation by dodecyl trimethylammonium bromide (DTAB) and thermal scanning was investigated. Sigmoidal denaturation curves were analysed according to the two states model of Pace theory to find the Gibbs free energy change of denaturation process in aqueous solution at room temperature, as a very good thermodynamic criterion indicating stability of the protein. Although His, Phe and Asp induced constriction of MT tertiary structure, its secondary structure had not any change and the result was a chemical and thermal stabilization of MT. The enzyme shows a proper coincidence of thermodyanamic and structural changes with the presence of trehalose. Thus, among the four osmolytes, trehalose is an exceptional protein stabilizer.     

保存温度和时间对狂犬病疫苗效力稳定性的影响

对人用精制狂犬病疫苗和浓缩狂犬疫苗分析在－33℃,2－8℃,25℃,37℃保存0－6个月进行效力的稳定性观察,结果表明随存放时间及温度增加,两者的生物活性均有不同程度的降低。在2－8℃条件下疫苗的效力明显比其它温度稳定（P＜0．02）;精制疫苗与浓缩疫苗比较,其效力有更稳定的趋势。