Efficacy of bacteriocin-based formula for reducing staphylococci, streptococci, and total bacterial counts on teat skin of dairy cows.

The use of teat dips is one of the most effective strategies to control mastitis by preventing new intramammary infections. Reducing bacterial load on teat skin helps control the spread of pathogens and spoilage and improves the quality of milk. The objective of this study was to evaluate the reduction of bacterial populations through the application of bacteriocin-based teat formulas. Teats of 12 Holstein cows received 2 different concentrations of bactofencin A, nisin, and reuterin alone or in combination, as well as iodine (positive control) and saline (negative control). Teat swabs were collected before and after application of teat formulas and analyzed for staphylococci, streptococci, and total bacteria counts. There were no differences for staphylococci, streptococci, and total bacterial counts for samples collected before application throughout the entire experiment. Reuterin-low and reuterin-high treatments reduced total bacterial count by 0.47 and 0.36 logs, respectively, whereas bactofencin A had no effect on any tested bacterial groups. Nisin-low treatment reduced staphylococci, streptococci, and total bacterial counts by 0.47, 0.30 and 0.50 logs, respectively. Nisin-high treatment resulted in 0.50, 0.50, and 0.47 log reduction for staphylococci, streptococci, and total bacterial counts. The bacteriocin consortium showed the highest reduction rates with 0.91, 0.54, and 0.90 log reductions obtained for staphylococci, streptococci, and total bacteria counts, respectively, for the low-concentration consortium. Similarly, the high-concentration consortium showed reduction rates with 0.95, 0.60, and 0.82 log reductions obtained for staphylococci, streptococci, and total bacteria counts, respectively. Thus, nisin and the bacteriocin consortium showed the most promise as a teat disinfectant by reducing staphylococci, streptococci, and total bacteria counts.

Partial prediction of the duration and the clinical status of Staphylococcus aureus bovine intramammary infections based on the phenotypic and genotypic analysis of isolates.

Staphylococcus aureus is a bacterial pathogen causing bovine intramammary infections (IMIs) often leading to chronic clinical or subclinical mastitis. Predicting the outcome of S. aureus IMIs (duration and clinical vs subclinical) based on the characterization of isolates would help to make better case management decisions. For this purpose, 583 S. aureus isolates from series of quarter milk samples were characterized by genotypic tests (detection of virulence genes seg, tst, lukM), epidemiological typing (spa type) and by a phenotypic test (biofilm production). VNTR typing (variable number of tandem repeats) was used to establish persistence of the same S. aureus strain in each series of sequential isolates. This allowed to associate each strain to a clinical/subclinical status and to validate the duration of infection. We found differences in the distribution of spa types between the strains from clinical and subclinical cases. Prevalence of lukM was also higher in strains from clinical cases than in strains from subclinical cases. A Kaplan-Meier analysis was then used to determine factors influencing the duration of the infection. Considering a multivariable model of the logistic regression, time to elimination was shorter with the strains of the subclinical lactation series compared to the clinical series (series with at least one clinical case). Strains from the spa type t359 and t529 were less likely to persist compared to those of spa type t13410. In sum, strain characterization including determination of the spa type helps to predict duration of infection and the clinical or subclinical outcome of S. aureus IMIs.

Genotypic and phenotypic characterization of Staphylococcus aureus causing persistent and nonpersistent subclinical bovine intramammary infections during lactation or the dry period.

Staphylococcus aureus is a significant pathogen frequently causing persistent intramammary infections (IMI) in dairy cows. We compared some genotypic and phenotypic characteristics of 285 strains collected from quarter milk samples from cows with persistent and nonpersistent subclinical IMI across Canada. Variable number of tandem repeats typing was used to infer the persistence of the same S. aureus strain in 3 consecutive quarter milk samples collected at intervals of 3 wk during lactation or before and after dry-off. All first isolates of the series were used as the representative strains from persistent IMI and were compared with nonpersistent strains for the presence of genes seg, sen, sec, and tst as well as by spa typing. Biofilm production in vitro and hld-RNAIII expression levels were also quantified. The gene seg was associated with a reduction in the likelihood of the bacteria to cause a persistent IMI during lactation. Strains persisting through the dry period produced significantly more biofilm in vitro than strains that do not persist after calving. Also, we showed that strains expressing more hld were more likely to be nonpersistent during either lactation or through the dry period. Three spa types were predominant (t529, t267, and a novel type: t13401). In the strains studied, the spa type tbl 2645 was the most frequent, and 97.0% of the strains of this spa type carried both sen and seg. Strains from the spa type tbl 2645 were less likely to cause a persistent IMI in the dry period. Most (86.7%) of the strains of the novel spa type (t13401) were negative for seg, sen, or both and produced significantly more biofilm in vitro than tbl 2645 and t267. The present study expanded our current knowledge on the genotypic and phenotypic traits of S. aureus strains recovered from persistent and nonpersistent IMI in Canada.

Experimental treatment of Staphylococcus aureus bovine intramammary infection using a guanine riboswitch ligand analog.

Staphylococcus aureus is a leading cause of intramammary infections (IMI). We recently demonstrated that Staph. aureus strains express the gene guaA during bovine IMI. This gene codes for a guanosine monophosphate synthetase and its expression is regulated by a guanine riboswitch. The guanine analog 2,5,6-triaminopyrimidine-4-one (PC1) is a ligand of the guanine riboswitch. Interactions between PC1 and its target result in inhibition of guanosine monophosphate synthesis and subsequent death of the bacterium. The present study describes the investigational use of PC1 for therapy of Staph. aureus IMI in lactating cows. The in vitro minimal inhibitory concentration of PC1 ranged from 0.5 to 4 µg/mL for a variety of Staph. aureus and Staphylococcus epidermidis strains and required a reducing agent for stability and full potency. A safety assessment study was performed, whereby the healthy quarters of 4 cows were infused with increasing doses of PC1 (0, 150, 250, and 500 mg). Over the 44 h following infusions, no obvious adverse effect was observed. Ten Holstein multiparous cows in mid lactation were then experimentally infused into 3 of the quarters with approximately 50 cfu of Staph. aureus strain SHY97-3906 and infection was allowed to progress for 2 wk before starting PC1 treatment. Bacterial counts reached then about 10(3) to 10(4) cfu/mL of milk. Infected quarters were treated with 1 of 3 doses of PC1 (0, 250, or 500 mg) after each morning and evening milking for 7d (i.e., 14 intramammary infusions of PC1). During the treatment period, milk from PC1-treated quarters showed a significant reduction in bacterial concentrations. However, this reduction of Staph. aureus count in milk was not maintained during the 4 wk following the end of the treatment and only 15% of the PC1-treated quarters underwent bacteriological cure. The somatic cell count and the quarter milk production were not affected by treatments. Although bacterial clearance was not achieved following treatment with PC1, these results demonstrate that the Staph. aureus guanine riboswitch represents a relevant and promising drug target for a novel class of antibiotics for the animal food industry.

The influence of body configuration on motor imagery of walking in younger and older adults.

Motor imagery (MI) refers to the mental simulation of a movement. It is used as a tool to improve motor function in several populations. In young adults, it has been repeatedly shown that MI of upper-limb movements is facilitated when one's posture is congruent with the movement to simulate. As MI training is notably used for improving locomotor-related activities in older populations, it may be questioned whether subjects' body configuration could also influence MI of walking movements and whether this influence is preserved with age. In the present study, we examined the impact of one's body position (congruent with walking: standing/incongruent with walking: sitting) on the duration of walking simulation over two distances (3m/6m), in 26 young (21 females, 5 males; mean: 23.2 ± 2.4 years) and 26 elderly (18 females, 8 males; mean: 72.7 ± 5.5 years) healthy subjects. It was found that, in both age groups, walking simulation times while standing were shorter than while sitting. Furthermore, walking simulation times in the standing position were closer to actual walking times to cover the same distances. The present findings extend to walking movements the notion that adopting a posture congruent with the movement to imagine facilitates the simulation process. They also suggest that, at least for simple walking tasks, this effect is maintained across the lifespan. The implication of our findings for optimizing MI training of locomotor-related activities is underlined.

Pathogenic and multidrug-resistant Escherichia fergusonii from broiler chicken.

An Escherichia spp. isolate, ECD-227, was previously identified from the broiler chicken as a phylogenetically divergent and multidrug-resistant Escherichia coli possessing numerous virulence genes. In this study, whole genome sequencing and comparative genome analysis was used to further characterize this isolate. The presence of known and putative antibiotic resistance and virulence open reading frames were determined by comparison to pathogenic (E. coli O157:H7 TW14359, APEC O1:K1:H7, and UPEC UTI89) and nonpathogenic species (E. coli K-12 MG1655 and Escherichia fergusonii ATCC 35469). The assembled genome size of 4.87 Mb was sequenced to 18-fold depth of coverage and predicted to contain 4,376 open reading frames. Phylogenetic analysis of 537 open reading frames present across 110 enteric bacterial species identifies ECD-227 to be E. fergusonii. The genome of ECD-227 contains 5 plasmids showing similarity to known E. coli and Salmonella enterica plasmids. The presence of virulence and antibiotic resistance genes were identified and localized to the chromosome and plasmids. The mutation in gyrA (S83L) involved in fluoroquinolone resistance was identified. The Salmonella-like plasmids harbor antibiotic resistance genes on a class I integron (aadA, qacEΔ-sul1, aac3-VI, and sulI) as well as numerous virulence genes (iucABCD, sitABCD, cib, traT). In addition to the genome analysis, the virulence of ECD-227 was evaluated in a 1-d-old chick model. In the virulence assay, ECD-227 was found to induce 18 to 30% mortality in 1-d-old chicks after 24 h and 48 h of infection, respectively. This study documents an avian multidrug-resistant and virulent E. fergusonii. The existence of several resistance genes to multiple classes of antibiotics indicates that infection caused by ECD-227 would be difficult to treat using antimicrobials currently available for poultry.

Genotype comparison of sorbitol-negative Escherichia coli isolates from healthy broiler chickens from different commercial farms.

Hybridization on arrays was used to assess the presence of virulence-associated genes and to determine the relatedness of 32 non-O157 sorbitol-negative Escherichia coli isolates from healthy broiler chickens. These isolates were from commercial farms that used feed supplemented with different antimicrobial agents (virginiamycin, bacitracin, salinomycin, narasin, nicarbazin, or diclazuril). For each isolate, fluorescent probes were made from genomic DNA and were hybridized on DNA arrays composed of genes associated with general functions, virulence, iron uptake systems, and DNA repair genes (e.g., mut genes). Hybridization on arrays results showed that isolates from the same farm tended to be clustered but actually represented 18 genetically distinct groups of isolates. Results revealed that some isolates showed similarity to human uropathogenic E. coli or avian pathogenic E. coli. Four avian pathogenic E. coli-like isolates were detected. Another isolate possessed the intimin gene (eaeA) and typical genes of the type 3 secretion system associated with enteropathogenic E. coli and enterohemorrhagic E. coli strains. Genes from a second system (secondary type 3 secretion system) homologous to that found in Salmonella Typhimurium were detected in many isolates. Several of the studied isolates also possessed the aerobactin, salmochelin, and yersiniabactin genes involved in iron acquisition in pathogenic bacteria. Our results clearly suggest that commensal E. coli isolates from chickens are reservoirs of virulence-associated genes and may represent colibacillosis and zoonotic risks.

Actual vs. best practices for young children with cerebral palsy: a survey of paediatric occupational therapists and physical therapists in Quebec, Canada.

RATIONALE: Cerebral palsy (CP) constitutes a substantial portion of paediatric rehabilitation, yet little is known regarding actual occupational therapy (OT) and physical therapy (PT) practices. This study describes OT and PT practices for young children with CP in Quebec, Canada. METHODS: This was a cross-sectional survey. All eligible, consenting paediatric occupational therapists (OTs) and physical therapists (PTs) were interviewed using a structured telephone interview based on vignettes of two typical children with CP at two age points--18 months and 4 years. Reported practices were grouped according to the International Classification of Functioning, Disability and Health (ICF). RESULTS: 91.9% of PTs (n=62; 83.8% participation rate) and 67.1% of OTs (n=85; 91.4% participation rate) reported using at least one standardized paediatric assessment. OT and PT interventions focused primarily on impairments and primary function (such as gait function and activities of daily living). Both professions gave little attention to interventions related to play and recreation/leisure. Clinicians reported the need for more training and education specific to CP and to the use of research findings in clinical practice. CONCLUSION: Wide variations and gaps were identified in clinicians' responses suggesting the need for a basic standard of OT and PT management as well as strategies to encourage knowledge dissemination regarding current best practice.

Helenalin reduces Staphylococcus aureus infection in vitro and in vivo.

Staphylococcus (S.) aureus is a major udder pathogen causing bovine mastitis. Some pro-inflammatory cytokines, including tumor necrosis factor-alpha (TNF-alpha), enhance extracellular and intracellular growth of S. aureus, indicating that the inflammatory process favors S. aureus infection. Helenalin is a sesquiterpene lactone with potent anti-inflammatory properties. This study was designed to evaluate the effects of helenalin on S. aureus infection. First, in vitro experiments were conducted. These studies revealed that proliferation of S. aureus in bovine mammary epithelial MAC-T cells treated in the presence or absence of TNF-alpha was markedly reduced in the presence of helenalin. Secondly, in vivo effects of helenalin were investigated. Lactating mice treated in the presence or absence of helenalin were challenged by the intramammary route with S. aureus and the bacteria in the mammary glands were counted 12 h after infection. Significantly less numbers of bacteria were recovered from the infected glands of helenalin-treated mice compared with untreated mice. Moreover, histological examination of mammary tissue from helenalin-treated mice that were challenged with S. aureus indicated that helenalin is able to significantly reduce leukocyte infiltration in the mammary gland following S. aureus inoculation. Our results show that helenalin reduces S. aureus intracellular growth and experimental S. aureus infection. We conclude that helenalin may be of potential interest in the treatment of S. aureus-induced mastitis in the bovine species.

Locomotor rehabilitation in a complex virtual environment.

Virtual reality (VR) technology offers a new and safe way to increase practice time and provide the varied environments and constraints needed to optimize locomotor training. Our specific objectives are (1) to create a virtual environment (VE) coupled with a self-paced treadmill for locomotor training; (2) to compare temporal and distance measurements of gait during treadmill walking while looking at different scenarios of VE; and (3) to develop a protocol optimized for the training of locomotor disorders after stroke. A motorized treadmill was mounted on a six-degree-of-freedom motion platform. VEs were created using commercial software (SoftImage) and projected on a large screen, while system control was administered through the CAREN software (Motek BV). The instantaneous treadmill speed and scene progression were servo-controlled. Preliminary results show that healthy subjects are able to have full control of their own walking speed both on the treadmill and within the virtual scene, while experiencing a strong sense of presence. A street crossing training protocol has been developed for locomotor training. It is expected that locomotor training with increasingly complex VEs will allow persons with stroke to increase progressively their locomotor capacity, as required and entrained by the VE.

Frontal and sagittal plane analyses of the stair climbing task in healthy adults aged over 40 years: what are the challenges compared to level walking?

OBJECTIVE: This study compared stair climbing and level walking in healthy adults aged over 40 years. DESIGN: Eleven subjects performed at their comfortable speed. BACKGROUND: The number of parameters studied during stair climbing has been limited, in particular in the frontal plane. METHODS: Time-distance parameters and three-dimensional kinematic data were obtained using foot-switches and an Optotrak system. Ground reaction forces were collected with a force platform embedded in the second step of the staircase or in the ground for level walking. Relative angles were calculated using a Cardanic rotation matrix and the net moments and the powers at the ankle, knee and hip joints were estimated with an inverse dynamic approach. RESULTS: A significant longer mean cycle duration and a shorter proportion of time in stance was obtained for stair climbing as compared to level walking. Profiles of the frontal plane joint angles, moments and powers indicated a different action of the hip abductors across tasks to control the pelvis in stance. Profiles of the sagittal plane confirmed the dominant role of the knee extensors during stair climbing but revealed also a knee-hip energy generation pattern that allows the avoidance of the intermediate step. CONCLUSIONS: Results suggest environment specific adaptations of the neuro-musculo-skeletal system that should be considered in the rehabilitation of stair climbing in patients. RELEVANCE: This study highlights the challenges of stair climbing compared to level walking in a within subject design. Key features of stair climbing that are important for the rehabilitation of step management are also reported.

Mechanisms of disturbed motor control in ankle weakness during gait after stroke.

This study investigated the role of paresis, excessive antagonist coactivation, increased muscle-tendon passive stiffness and spasticity in the reduced stance phase plantarflexor moment (Mmax) and swing phase dorsiflexion during gait (DFmax) in subjects with a recent (<6 months post-stroke) hemiparesis (patients). The gait pattern of the paretic and non-paretic sides was evaluated in 30 patients (aged 57.8+/-10.8 years), whereas only one side was evaluated in 15 healthy controls (aged 59.1+/-9.8 years) while walking at natural and very slow speeds. Peak plantarflexor moment (Mmax) and peak medial gastrocnemius (MG) activation during the stance phase, as well as peak dorsiflexion angle (Dfmax) and peak tibialis anterior (TA) activation during the swing phase, were retained for analysis. In addition, a coactivation index and a plantarflexor spasticity index were calculated for both the stance and the swing phase, and plantarflexor passive stiffness was evaluated on an isokinetic dynamometer. The results showed that Mmax on the paretic and non-paretic sides were both reduced compared with control values at natural speed. This reduction was combined to a low MG activation (paresis) on the paretic side. On the non-paretic side, the reduced plantarflexor moment was related to excessive coactivation levels. The swing phase Dfmax tended to be reduced (not significantly) on the paretic side of the patients compared with control values. This reduction was neither associated with excessive antagonist coactivation nor to plantarflexor hyperactive stretch reflexes, but rather to an increased plantarflexor passive stiffness. In some of the patients, however, an increased TA activation that overcame the plantarflexor passive stiffness allowed for normal DFmax values. The functional consequences of the disturbed mechanisms of motor control observed in both the paretic and non-paretic sides are discussed.

Locomotor-specific measure of spasticity of plantarflexor muscles after stroke.

OBJECTIVES: To study the stretch reflex excitability (spasticity) of the plantarflexor muscles during gait in patients with hemiparesis and to study the relationships of spasticity during gait with spasticity at rest and gait speed. DESIGN: Cross-sectional, descriptive. SETTING: Rehabilitation center. PARTICIPANTS: Convenience sample of 30 patients (58 +/- 11yr) with hemiparesis (<6mo poststroke) and 15 healthy controls (59 +/- 8yr). INTERVENTIONS: Patients walked at natural speed, healthy subjects at very slow speed for 10 gait cycles. Electromyographic activation of the medial gastrocremius was recorded by using surface electrodes. A 2-dimensional video camera system with reflective markers was used to acquire kinematics of the lower limbs. MAIN OUTCOME MEASURES: Electromyography-lengthening velocity slopes, calculated from measures obtained during the lengthening periods of the medial gastrocnemius muscle during the stance and the swing phases. Measured spatisticity (Modified Ashworth Scale [MAS]), static strength (ankle clonus), and motor control (Fugl-Meyer test). RESULTS: Velocity-sensitive electromyographic responses, indicative of hyperactive stretch reflexes, were found on the paretic side during the stance phase of gait (in 66% of the patients), but not on the nonparetic side or in controls. In many patients, velocity-sensitive responses coexisted with low plantarflexor activation levels during the stance phase. No clear patterns of response were measured during the swing phase in either group. Spasticity during gait in the patients was found to be positively related (r = .47, p < .01; r = .57, p < .001) to spasticity at rest (MAS; ankle clonus), whereas it was found to be negatively related to gait speed (r = -.47 to -.53, p < .01). CONCLUSIONS: The validity of the present method is supported by the fact that it is locomotor-specific and that it allowed for a good discrimination between spastic and nonspastic limbs, as well as between stance and swing phases of the gait cycle. The results also support plantarflexor spasticity as a factor contributing to the poor locomotor performance after stroke.

Walking speed over 10 metres overestimates locomotor capacity after stroke.

OBJECTIVE: To examine 10-m comfortable walking speed and 6-minute distance in healthy individuals and individuals after stroke and to assess the level of disability associated with poor walking endurance after stroke. DESIGN: Descriptive study in which comfortable walking speed over 10 m and distance covered in 6 minutes (6-minute walk test) were compared between healthy subjects and subjects after stroke. SUBJECTS: Twelve healthy subjects and 14 subjects after stroke. MAIN OUTCOME MEASURES: Walking speed and 6-minute distances were compared between groups. In addition, for each group, actual distance walked in 6 minutes was compared with the distance predicted by the 10-m walking speed test and the distance predicted by normative reference equations. RESULTS: Subjects after stroke had significant reductions in 10-m speed and 6-minute distance compared with healthy subjects (p < 0.05). Subjects after stroke were not able to maintain their comfortable walking speed for 6 minutes, whereas healthy subjects walked in excess of their comfortable speed for 6 minutes. The average distance walked in 6 minutes by individuals after stroke was only 49.8+/-23.9% of the distance predicted for healthy individuals with similar physical characteristics. CONCLUSION: In our subjects after stroke, walking speed over a short distance overestimated the distance walked in 6 minutes. Both walking speed and endurance need to be measured and trained during rehabilitation.

Potential role of mental practice using motor imagery in neurologic rehabilitation.

For many patients with damage to the central nervous system (CNS), execution of motor tasks is very difficult, sometimes impossible, even after early participation in an active rehabilitation program. Several investigators have recently proposed that mental practice could be used by these patients as a therapeutic tool to improve their performance of motor functions, yet very little empirical work addresses this issue directly. This article discusses the rationale for investigating mental practice as a means of promoting motor recovery in patients with a neurologic disorder. We first present evidence supporting the existence of a similarity between executed and imagined actions using data from psychophysical, neurophysiologic, and brain imaging studies. This parallel is then extended to the repetition of movements during physical and mental practice of a motor skill. Finally, a new model is proposed to emphasize the key role of motor imagery as an essential process of mental practice, and also to stimulate additional research on this type of training in the rehabilitation of patients with motor impairments of cerebral origin.

In vitro activities of RWJ-54428 (MC-02,479) against multiresistant gram-positive bacteria.

RWJ-54428 (MC-02,479) is a new cephalosporin with a high level of activity against gram-positive bacteria. In a broth microdilution susceptibility test against methicillin-resistant Staphylococcus aureus (MRSA), RWJ-54428 was as active as vancomycin, with an MIC at which 90% of isolates are inhibited (MIC(90)) of 2 microg/ml. For coagulase-negative staphylococci, RWJ-54428 was 32 times more active than imipenem, with an MIC(90) of 2 microg/ml. RWJ-54428 was active against S. aureus, Staphylococcus epidermidis, and Staphylococcus haemolyticus isolates with reduced susceptibility to glycopeptides (RWJ-54428 MIC range, < or = 0.0625 to 1 microg/ml). RWJ-54428 was eight times more potent than methicillin and cefotaxime against methicillin-susceptible S. aureus (MIC(90), 0.5 microg/ml). For ampicillin-susceptible Enterococcus faecalis (including vancomycin-resistant and high-level aminoglycoside-resistant strains), RWJ-54428 had an MIC(90) of 0.125 microg/ml. RWJ-54428 was also active against Enterococcus faecium, including vancomycin-, gentamicin-, and ciprofloxacin-resistant strains. The potency against enterococci correlated with ampicillin susceptibility; RWJ-54428 MICs ranged between < or = 0.0625 and 1 microg/ml for ampicillin-susceptible strains and 0.125 and 8 microg/ml for ampicillin-resistant strains. RWJ-54428 was more active than penicillin G and cefotaxime against penicillin-resistant, -intermediate, and -susceptible strains of Streptococcus pneumoniae (MIC(90)s, 0.25, 0.125, and < or = 0.0625 microg/ml, respectively). RWJ-54428 was only marginally active against most gram-negative bacteria; however, significant activity was observed against Haemophilus influenzae and Moraxella catarrhalis (MIC(90)s, 0.25 and 0.5 microg/ml, respectively). This survey of the susceptibilities of more than 1,000 multidrug-resistant gram-positive isolates to RWJ-54428 indicates that this new cephalosporin has the potential to be useful in the treatment of infections due to gram-positive bacteria, including strains resistant to currently available antimicrobials.

Anticipatory locomotor control for obstacle avoidance in mid-childhood aged children.

The present work explored the anticipatory locomotor adjustments during obstacle avoidance by eight children aged 7--9 years. Analyses involved kinematic, kinetic and muscle mechanical power patterns at each lower limb joint, as well as electromyographic data from five muscles. The children demonstrated adult-like limb displacements and general dynamic strategies for obstacle clearance. However, when normalized to body mass, amplitudes of certain muscle power bursts related to anticipatory locomotor adjustments were decreased from those reported in the literature for adults, and an absence of the usual antagonistic knee extensor power burst at the end of the stance phase was frequently observed. The data suggest that the expression of anticipatory locomotor adjustments is still maturing during mid-childhood.

Coactivation during gait as an adaptive behavior after stroke.

The aims of the present study were to quantify the impairment in ankle coactivation on the paretic and non-paretic sides of subjects with hemiparesis and to examine the relationship of ankle coactivation with postural instability, motor deficit of the paretic lower extremity and locomotor performance. Electromyography of the medial gastrocnemius (MG) and tibialis anterior (TA) muscles were recorded bilaterally during gait in 30 subjects (62.1+/-9.9 years) who had suffered a recent stroke (<6 months) as well as on one side of 17 healthy controls (59.3+/-9.1 years) walking at very slow speed. Ankle muscle coactivation was calculated by dividing the time of overlap between MG and TA signals (threshold of 20 microV) by the duration of the gait phases of interest: stance, swing, first and second double support sub-phases and single support sub-phase. The time spent in single support and the peak plantarflexor moment of force on the paretic side were used to measure, respectively, postural stability and dynamic strength of the paretic plantarflexors. The subjects with hemiparesis demonstrated less coactivation on the paretic side during the single support sub-phase (p<0.01) and more coactivation during first and second double support sub-phases on the non-paretic side (p<0.001) compared to control values. The patients with coactivation patterns that differed the most from controls were the patients with the more severe impairments and disabilities. While the reduced coactivation on the paretic side may contribute to poor postural stability and poor locomotor performance, the presence of excessive coactivation on the non-paretic side when both limbs were in ground contact may be an adaptation to help maintain postural stability during gait.

Three-dimensional gait analysis in women with a total hip arthroplasty.

OBJECTIVES: The purposes of this study were: (1) to identify the primary (hip) and secondary (neighboring joints) impairments during gait in subjects with a total hip arthroplasty total hip arthroplasty, (2) to determine which impairments persist when controlling for gait speed and (3) to study the relationships between primary and secondary impairments in order to describe the locomotor strategies used by these patients.DESIGN. This cross-sectional study compared the gait patterns of women with a total hip arthroplasty to those of healthy women.BACKGROUND. Several studies have reported residual hip impairments in the sagittal plane during gait after a total hip arthroplasty. There is, however, a substantial lack of knowledge in regard to the changes at the neighboring joints and in the other planes of movement.METHODS. Subjects have been examined during a gait laboratory testing session including the simultaneous recording of three-dimensional kinematics and ground reaction forces on one side, and bilateral activation of six lower limb muscles.RESULTS. A significant decrease of 20% in the hip extensor moment of force during the early stance phase was correlated (R(2)=43%) with a significant decrease of 14% in gait speed. Moreover, a significant decrease of 59% in the range of hip extension at the end of the stance phase was observed together with secondary impairments such as a significant increase in the anterior pelvic rotation, in knee flexion and in ankle dorsiflexion. Lastly, a significant increase in ipsilateral bending of the trunk during the single limb support on the operated limb was concomitant with a significant decrease in the hip abductor moment of force.CONCLUSIONS. The decrease in gait speed and the persistence of abnormal gait patterns one year after the total hip arthroplasty were associated respectively with a decrease in the hip extensor moment of force and with a decrease in the range of hip extension (sagittal plane) or in the hip abductor moment of force (frontal plane). RelevanceThe data provided in this paper may serve as guidelines to establish rehabilitation programs designed to restore optimal locomotor function.

Preparatory adjustments during gait initiation in 4-6-year-old children.

The preparatory adjustments related to gait initiation in a group of six children (4-6 years old) were studied in comparison to a group of six adults (50-61 years old). Muscle activity, ground reaction forces and body kinematics were recorded during the initiation of gait in subjects standing with one foot on each of two forceplates. Like adults, children had consistent anticipatory activations of the tibialis anterior (TA) muscle accompanied by center of pressure (COP) displacements, but the relative magnitude of both the backward COP displacement and concomitant initial TA activation burst were lower (P<0.03 and P<0.001 respectively) in children. The latter findings were associated with a lower rate of forward progression in children (P=0.01), and a lack of significant covariance between the backward shift and forthcoming velocity. In contrast, the preparatory adjustments in the medio-lateral (M/L) direction were prominent in children. Larger M/L peak force rates in children (P=0. 01) were associated with an earlier (P=0.007) weight transfer to the stance limb; moreover, children initiated gait from a wider (P=0.04) base of support and had a trajectory of the total COP that was lateral rather than posterior like in adults. The consistent preparatory adjustment responses indicate that the motor program for initiating gait is functional at this age. The prominence of the preparatory adjustments in the M/L direction together with a reduced magnitude of the responses in the antero-posterior direction suggest that the anticipatory behavior for initiating gait develops first in the frontal plane and that more walking experience and better postural stability are required to fully achieve the adult-like control of the gait initiation process.