Temporal Coordination of the Sit-to-Walk Task in Subjects With Stroke and in Controls

Differences in paretic lower limb loading and fluidity in sit-to-walk according to selection of the leading limb in individuals with stroke

BACKGROUND

Sit-to-walk is an asymmetric task that is challenging for individuals with stroke, and paretic limb loading at seat-off and movement fluidity may change according to whether the non-paretic or paretic leg is used as the leading limb. This study aimed to investigate differences in paretic limb loading and fluidity depending on whether the non-paretic limb or paretic limb was used as the leading limb.

METHODS

Thirty-eight individuals with stroke performed sit-to-walk with each leg as the leading limb, and their movements were measured using a 3D motion analysis system. The paired t-test or Wilcoxon signed-rank test was used to assess differences according to limb selection in paretic limb loading ratio at seat-off and fluidity (Fluidity Index: ratio of the lowest to peak forward velocity before first initial contact).

FINDINGS

Twenty-two of 38 participants preferred to use the paretic limb as the leading limb. When leading with the paretic limb, the paretic limb loading ratio was significantly larger (p = 0.002), and the Fluidity Index was lower (p = 0.007).

INTERPRETATION

Sit-to-walk with the paretic leading limb seems to be an adaptive movement because many participants preferred leading with the paretic limb. However, selection of the leading limb in sit-to-walk involves a biomechanical tradeoff between paretic limb loading at seat-off and movement fluidity in individuals with stroke. Use of the paretic leading limb requires loading capacity of this limb, and the non-paretic leading limb must have high balance ability to merge sit-to-stand and gait initiation.

Analysis of 15 different pelvis marker protocols during sit-to-stand

Sit-to-stand (STS) is a common transition movement needed to perform daily tasks. Previously, the kinematics of the STS movement has been investigated using optical motion capture. This method uses cameras and reflective markers on the body to capture movements. During STS, these markers can be difficult to measure due to blocked vision from the chair's arm- and backrest. This can result in poor data quality. The aim of this study was to investigate 15 different marker protocols and compare them in terms of visibility and selected outcome measures: hip flexion mean angle and range of motion (ROM). Fourteen healthy subjects completed five successful trials of STS. Marker protocols consisted of three anterior marker protocols and five posterior marker protocols, combined into a total of 15 marker protocols. For visibility, the traditional pelvis marker protocol proved unsuitable for STS tracking. Marker pins or additional markers anteriorly, and sacrum markers posteriorly, proved to be more suitable alternatives. For hip flexion mean angle and ROM, the estimates had similar tendencies. Hence, marker protocols were not outcome measure specific. Anteriorly, marker pins resulted in similar estimates as the traditional pelvis marker protocol. Posteriorly, sacrum markers estimated a smaller hip flexion angle, compared to the traditional pelvis marker protocol. In conclusion, marker pins can be used instead of regular ASIS markers at anterior pelvis. Posteriorly, sacrum markers can be used instead of PSIS markers.

Investigating the Relationships Between Three Important Functional Tasks Early After Stroke: Movement Characteristics of Sit-To-Stand, Sit-To-Walk, and Walking

Background: Walking, sit-to-stand (STS) and sit-to-walk (STW) are all considered important functional tasks in achieving independence after stroke. Despite knowledge that sensitive measurement of movement patterns is crucial to understanding neuromuscular restitution, there is surprisingly little information available about the detailed biomechanical characteristics of, and relationships between, walking, sit-to-stand and sit-to-walk, particularly in the important time window early after stroke. Hence, here, the study aimed to:

Identify the biomechanical characteristics of and determine any differences in both movement fluidity (hesitation, coordination and smoothness) and duration of movement phases, between sit-to-stand (STS) and sit-to-walk (STW) in people early after stroke.

Determine whether measures of movement fluidity (hesitation, coordination, and smoothness) and movement phases during sit-to-stand (STS) and/or sit-to-walk (STW) are correlated strongly to commonly used measures of walking speed and/or step length ratio in people early after stroke.

Methods: This study consisted of secondary data analysis from the SWIFT Cast Trial. Specifically, we investigated movement fluidity using established assessments of smoothness, hesitation and coordination and the time duration for specific movement phases in a group of 48 people after stroke. Comparisons were made between STS and STW and relationships to walking measures were explored.

Results: Participants spent significantly more time in the initial movement phase, flexion momentum, during STS [mean time (SD) 1.74 ±1.45 s] than they did during STW [mean time (SD) 1.13 ± 1.03 s]. STS was also completed more smoothly but with more hesitation and greater coordination than the task of STW. No strong relationships were found between movement fluidity or duration with walking speed or step length symmetry.

Conclusions: Assessment of movement after stroke requires a range of functional tasks and no one task should predominate over another. Seemingly similar or overlapping tasks such as STS and STW create distinct biomechanical characteristics which can be identified using sensitive, objective measures of fluidity and movement phases but there are no strong relationships between the functional tasks of STS and STW with walking speed or with step-length symmetry.

Identifying consistent biomechanical parameters across rising-to-walk subtasks to inform rehabilitation in practice: A systematic literature review

BACKGROUND

The best approach to rehabilitate the control of everyday whole-body movement (e.g. rise-to-walk) after pathology remains unclear in part because the associated controlled performance variables are not known. Rise-to-walk can be performed fluidly (sit-to-walk) or non-fluidly (sit-to-stand, proceeded by gait-initiation). Biomechanical variables that remain consistent in health regardless of how rise-to walk is performed represent controlled performance variable candidates which could monitor rehabilitative change.

RESEARCH QUESTION

To determine if any biomechanical parameters remain consistent across rising-to-walk (RTW) subtasks (sit-to-stand, gait-initiation, and sit-to-walk) in healthy adults for purposes of movement control assessment in clinical practice.

METHODS

Data sources included Medline, Cinahl, and Scopus databases, and the grey literature. Study selection was based on eligibility criteria and must have reported spatiotemporal, kinematic and/or kinetic biomechanical parameters featuring >1 RTW subtask. Data extraction and synthesis; standardised-mean-differences (SMDs) were calculated (pooled if replicated in >1 study) for each parameter. Consistency was determined if SMD95 %CIs included the zero-effect line.

RESULTS

Nine studies (n = 99) were included (40 ± 7.5yrs). Seven parameters were replicated in >1 study and subjected to meta-analysis (fixed-effect model). Two were consistent between sit-to-stand and sit-to-walk: flexion-momentum time (M(95 %CI) = 0.055(-0.423 to 0.533); p = 0.823) and peak whole-body-centre-of-mass vertical velocity (M(95 %CI)= -0.415(-0.898 to 0.069); p = 0.093); and centre-of-pressure to whole-body-centre-of-mass distance at toe-off (M(95 %CI)= -0.137(-0.712 to 0.439); p = 0.642) between gait-initiation and sit-to-walk. Another 20 parameters were consistent based on single-study SMDs.

SIGNIFICANCE

Consistent parameters might exist across RTW subtasks. However, the evidence is based on few studies with small samples and variable RTW protocols. Future studies designed to confirm consistency using a standardised RTW protocol are needed.

Gait-initiation onset estimation during sit-to-walk: Recommended methods suitable for healthy individuals and ambulatory community-dwelling stroke survivors

Background

Gait-initiation onset (GI-onset) during sit-to-walk (STW) is commonly defined by mediolateral ground-reaction-force (xGRF) rising and crossing a threshold pre-determined from sit-to-stand peak xGRF. However, after stroke this method [xGRFthresh] lacks validity due to impaired STW performance. Instead, methodologies based upon instance of swing-limb maximum-vertical-GRF [vGRFmaxSWING], maximum-xGRF [xGRFmax], and swing-limb heel-off [firstHEELoff] can be applied, although their validity is unclear. Therefore, we determined these methodologies’ validity by revealing the shortest transition-time (seat-off–GI-onset), their utility in routinely estimating GI-onset, and whether they exhibited satisfactory intra-subject reliability.

Methods

Twenty community-dwelling stroke (60 (SD 14) years), and twenty-one age-matched healthy volunteers (63 (13) years) performed 5 standardised STW trials with 2 force-plates and optical motion-tracking. Transition-time differences across-methods were assessed using Friedman tests with post-hoc pairwise-comparisons. Within-method single-measure intra-subject reliability was determined using ICC_3,1 and standard errors of measurement (SEMs).

Results

In the healthy group, median xGRFthresh transition-time was significantly shorter than xGRFmax (0.183s). In both the healthy and stroke groups, xGRFthresh transition-times (0.027s, 0.695s respectively) and vGRFmaxSWING (0.080s, 0.522s) were significantly shorter than firstHEELoff (0.293s, 1.085s) (p<0.001 in all cases). GI-onset failed to be estimated in 48% of stroke trials using xGRFthresh. Intra-subject variability was relatively high but was comparable across all estimation methods.

Conclusion

The firstHEELoff method yielded significantly longer transition-times. The xGRFthresh method failed to routinely produce an estimation of GI-onset estimation. Thus, with all methods exhibiting low, yet comparable intra-subject repeatability, averaged xGRFmax or vGRFmaxSWING repeated-measures are recommended to estimate GI-onset for both healthy and community-dwelling stroke individuals.

Parameters that remain consistent independent of pausing before gait-initiation during normal rise-to-walk behaviour delineated by sit-to-walk and sit-to-stand-and-walk

BACKGROUND

Rising-to-walk is an everyday transitional movement task rarely employed in gait rehabilitation. Sit-to-walk (STW) and sit-to-stand-and-walk (STSW), where a pause separates sit-to-stand and gait-initiation (GI) represent extremes of rising-to-walk behaviour. Delayed GI can indicate pathological impairment but is also observed in healthy individuals. We hypothesise that healthy subjects express consistent biomechanical parameters, among others that differ, during successful rising-to-walk task performance regardless of behaviour. This study therefore sought to identify if any parameters are consistent between STW and STSW in health because they represent normal rise-to-walk performance independent of pause, and also because they represent candidate parameters sensitive enough to monitor change in pathology.

METHODS

Ten healthy volunteers performed 5 trials of STW and STSW. Event timing, ground-reaction-forces (GRFs), whole-body-centre-of-mass (BCoM) displacement, and centre-of-pressure (CoP) to extrapolated BCoM (xCoM) distance (indicator of positional stability) up to the 3rd step were compared between-tasks with paired t-tests. For consistent parameters; agreement between-tasks was assessed using Bland-Altman analyses and minimal-detectable-change (MDC) calculations.

RESULTS

Mean vertical GRFs, peak forward momentum and fluidity during rising; CoP-xCoM separation at seat-off, upright, GI-onset, and steps1-2; and forward BCoM velocity were all significantly greater in STW. In contrast, peak BCoM vertical momentum, flexion-momentum time, and 3rd step stability were consistent between tasks and yielded acceptable reliability.

CONCLUSION

STW is a more challenging task due to the merging of rising with GI reflected by greater CoP-xCoM separation compared to STSW indicative of more positional instability. However, BCoM vertical momentum, flexion-momentum time, and step3 stability remained consistent in healthy individuals and are therefore candidates with which to monitor change in gait rehabilitation following pathology. Future studies should impose typical pause-durations observed in pathology upon healthy subjects to determine if the parameters we have identified remain consistent.

A technique to record the sedentary to walk movement during free living mobility: A comparison of healthy and stroke populations

BACKGROUND

Hesitation between moving from a sedentary posture (lying/sitting) to walking is a characteristic of mobility impaired individuals, as identified from laboratory studies. Knowing the extent to which this hesitation occurs during everyday life would benefit rehabilitation research. This study aimed to quantify this transition hesitation through a novel approach to analysing data from a physical activity monitor based on a tri-axial accelerometer and compare results from two populations; stroke patients and age-matched unimpaired controls.

METHODS

Stroke patients living at home with early supported discharge (n=34, 68.9YO±11.8) and age-matched controls (n=30, 66.8YO±10.5) wore a physical activity monitor for 48h. The outputs from the monitor were then used to determine the transitions from sedentary to walking. The time delay between a sedentary posture ending and the start of walking classified four transition types: 1) fluent (<=2s), 2) hesitant (>2s<=10s), 3) separated (>10s) and 4) a change from sedentary with no registered walking to a return to sedentary.

RESULTS

Control participants initiated walking after a sedentary posture on 92% of occasions. Most commonly (43%) this was a fluent transition. In contrast stroke patients walked after changing from a sedentary posture on 68% of occasions with only 9% of transitions classed as fluent, (p<0.05).

DISCUSSION/ CONCLUSION

A new data analysis technique reports the frequency of walking following a change in sedentary position in stroke patients and healthy controls and characterises this transition according to the time delay before walking. This technique creates opportunities to explore everyday mobility in greater depth.

Timed Up and Go test: Comparison of kinematics between patients with chronic stroke and healthy subjects

Understanding locomotor behavior is important to guide rehabilitation after stroke. This study compared lower-limb kinematics during the walking and turning sub-tasks of the Timed Up and Go (TUG) test in stroke patients and healthy subjects. We also determined the parameters which explain TUG sub-task performance time in healthy subjects. Biomechanical parameters were recorded during the TUG in standardized conditions in 25 healthy individuals and 29 patients with chronic stroke using a 3D motion-analysis system. Parameters were compared between groups and a stepwise regression was used to indicate parameters which explained performance time in the healthy subjects. The percentage difference in step length between the last and first steps was calculated, during walking sub-tasks for each group. Speed, cadence, step length, percentage paretic single support phase, percentage non-paretic swing phase, peak hip extension, knee flexion and ankle dorsiflexion were significantly reduced in the Stroke group compared to the Healthy group (p<0.05). In the Healthy group, step length and cadence explained 91% of variance for Go and 86% for Return (walking sub-tasks), and none of the parameters explained the Turn. Previous study in patients with stroke showed that the same parameters explained the variance during the walking sub-tasks and balance-related parameters explained the Turn. The present results showed that step length was differently modulated in each group. Thus the locomotor behavior of patients with stroke during obstacle circumvention is quite specific in light of the results obtained in healthy subjects.

Sit-to-stand-and-walk from 120% Knee Height: A Novel Approach to Assess Dynamic Postural Control Independent of Lead-limb

Individuals with sensorimotor pathology e.g., stroke have difficulty executing the common task of rising from sitting and initiating gait (sit-to-walk: STW). Thus, in clinical rehabilitation separation of sit-to-stand and gait initiation - termed sit-to-stand-and-walk (STSW) - is usual. However, a standardized STSW protocol with a clearly defined analytical approach suitable for pathological assessment has yet to be defined. Hence, a goal-orientated protocol is defined that is suitable for healthy and compromised individuals by requiring the rising phase to be initiated from 120% knee height with a wide base of support independent of lead limb. Optical capture of three-dimensional (3D) segmental movement trajectories, and force platforms to yield two-dimensional (2D) center-of-pressure (COP) trajectories permit tracking of the horizontal distance between COP and whole-body-center-of-mass (BCOM), the decrease of which increases positional stability but is proposed to represent poor dynamic postural control. BCOM-COP distance is expressed with and without normalization to subjects' leg length. Whilst COP-BCOM distances vary through STSW, normalized data at the key movement events of seat-off and initial toe-off (TO1) during steps 1 and 2 have low intra and inter subject variability in 5 repeated trials performed by 10 young healthy individuals. Thus, comparing COP-BCOM distance at key events during performance of an STSW paradigm between patients with upper motor neuron injury, or other compromised patient groups, and normative data in young healthy individuals is a novel methodology for evaluation of dynamic postural stability.

Sit-to-walk and sit-to-stand-and-walk task dynamics are maintained during rising at an elevated seat-height independent of lead-limb in healthy individuals

INTRODUCTION

Sit-to-walk (STW) is a common transitional motor task not usually included in rehabilitation. Typically, sit-to-stand (STS), pause, then gait initiation (GI) before walking is used, which we term sit-to-stand-and-walk (STSW). Separation between centre-of-pressure (COP) and whole-body centre-of-mass (BCOM) during GI is associated with dynamic postural stability. Rising from seats higher than knee-height (KH) is more achievable for patients, but whether this and/or lead-limb significantly affects task dynamics is unclear. This study tested whether rising from seat-heights and lead-limb affects STW and STSW task dynamics in young healthy individuals.

METHODS

Ten (5F) young (29±7.7 years) participants performed STW and STSW from a standardised position. Five trials of each task were completed at 100 and 120%KH leading with dominant and non-dominant legs. Four force-plates and optical motion capture delineated key movement events and phases with effect of seat-height and lead-limb determined by 2-way ANOVA within tasks.

RESULTS

At 120%KH, lower peak vertical ground-reaction-forces (vGRFs) and vertical BCOM velocities were observed during rising irrespective of lead-limb. No other parameters differed between seat-heights or lead-limbs. During GI in STSW there was more lateral, and less posterior, COP excursion than expected.

CONCLUSION

Reduction in vGRFs and velocity during rising at 120%KH is consistent with reduced effort in young healthy individuals and is likely therefore to be an appropriate seat-height for patients. Lead-limb had no effect upon STSW or STW parameters suggesting that normative data independent of lead-limb can be utilised to monitor motor rehabilitation should differences be observed in patients. STSW should be considered an independent movement transition.

Locomotor Trajectories of Stroke Patients during Oriented Gait and Turning

Background

The Timed Up and Go (TUG) test is widely used to assess locomotion in patients with stroke and is considered to predict the risk of falls. The analysis of locomotor trajectories during the TUG appears pertinent in stroke patients. The aims of this study were i) to analyze locomotor trajectories in patients with stroke during the walking and turning sub-tasks of the TUG, and to compare them with healthy subjects, ii) to determine whether trajectory parameters provide additional information to that provided by the conventional measure (performance time), iii) to compare the trajectory parameters of fallers and non-fallers with stroke and of patients with right and left hemisphere stroke, and iv) to evaluate correlations between trajectory parameters and Berg Balance Scale scores.

Methods

29 patients with stroke (mean age 54.2±12.2 years, 18 men, 8 fallers) and 25 healthy subjects (mean age 51.6±8.7 years, 11 men) underwent three-dimensional analysis of the TUG. The trajectory of the center of mass was analyzed by calculation of the global trajectory length, Hausdorff distance and Dynamic Time Warping. The parameters were compared with a reference trajectory during the total task and each sub-task (Go, Turn, Return) of the TUG.

Results

Values of trajectory parameters were significantly higher for the stroke group during the total TUG and the Go and Turn sub-tasks (p<0.05). Moreover, logistic regression indicated that these parameters better discriminated stroke patients and healthy subjects than the conventional timed performance during the Go sub-task. In addition, fallers were distinguished by higher Dynamic Time Warping during the Go (p<0.05). There were no differences between patients with right and left hemisphere stroke.

Discussion and Conclusion

The trajectories of the stroke patients were longer and more deviated during the turn and the preceding phase. Trajectory parameters provided additional information to timed performance of this locomotor task. Focusing rehabilitation programs on lead-up to turn and turning could be relevant for stroke patients since the Turn was related to the balance and the phase preceding the turn seemed to distinguish fallers.

Sit-to-walk Task in Hemiplegic Stroke Patients: Relationship between Movement Fluidity and the Motor Strategy in Initial Contact

PURPOSE

Generally, stroke patients can walk and stand up fluidly but fulfill the sit-to-walk (STW) task with difficulty. The purpose of this study was to investigate the relationship between movement fluidity and motor strategy in the initial contact of the STW task.

METHOD

Thirty stroke patients and ten healthy subjects performed the STW task from a sitting position, and their movement was measured by a motion analysis system. The differences in data between patients and healthy subjects were analyzed using the Mann-Whitney U test. The relationship between fluidity index (FI) and other indices (kinetic and kinematic data in STW, functional independence measure [FIM], and Fugl-Meyer Assessment [FMA]) were analyzed using Spearman's rank correlation coefficient.

RESULTS

The stroke patients had lower FI values than the healthy subjects and exhibited shortened step length and prolonged duration from onset to the first stance leg off. FI values correlated with trunk flexure angle at initial contact, first step length, and maximum vertical floor reaction force. The independent level of the FIM of stair climbing and walking ability and the FMA of balance also correlated with FI.

CONCLUSION

There is a possibility that poor balance is one of the reasons why stroke patients are unable to start walking fluently from the sitting position. To perform the STW fluidly, patients must start walking before the trunk extension is fully completed. The relationship between FI and indices of physical ability, namely stair climbing and balance, may have therapeutic benefits for coaching the STW task to stroke patients.

Dynamic Stability and Risk of Tripping during the Timed Up and Go Test in Hemiparetic and Healthy Subjects

Background

The Timed Up and Go (TUG) test is often used to estimate risk of falls. Foot clearance and displacement of the center of mass (COM), which are related to risk of tripping and dynamic stability have never been evaluated during the TUG. Accurate assessment of these parameters using instrumented measurements would provide a comprehensive assessment of risk of falls in hemiparetic patients. The aims of this study were to analyze correlations between TUG performance time and displacement of the COM and foot clearance in patients with stroke-related hemiparesis and healthy subjects during the walking and turning sub-tasks of the TUG and to compare these parameters between fallers and non-fallers.

Methods

29 hemiparetic patients and 25 healthy subjects underwent three-dimensional gait analysis during the TUG test. COM and foot clearance were analyzed during the walking and turning sub-tasks of the TUG.

Results

Lateral displacement of the COM was greater and faster during the walking sub-tasks and vertical displacement of the COM was greater during the turn in the patients compared to the healthy subjects (respectively p<0.01 and p<0.05). Paretic foot clearance was greater during walking and displacement of the COM was slower during the turn in the patients (p<0.01). COM displacement and velocity during the turn were correlated with TUG performance in the patients, however, vertical COM displacement was not. These correlations were significant in the healthy subjects. There were no differences between COM parameters or foot clearance in fallers and non-fallers.

Discussion and Conclusion

Hemiparetic patients are less stable than healthy subjects, but compensate with a cautious gait to avoid tripping. Instrumented analysis of the TUG test appears relevant for the assessment of dynamic stability in hemiparetic patients, providing more information than straight-line gait.

Spatiotemporal and Kinematic Parameters Relating to Oriented Gait and Turn Performance in Patients with Chronic Stroke

Background

The timed up and go test (TUG) is a functional test which is increasingly used to evaluate patients with stroke. The outcome measured is usually global TUG performance-time. Assessment of spatiotemporal and kinematic parameters during the Oriented gait and Turn sub-tasks of the TUG would provide a better understanding of the mechanisms underlying patients’ performance and therefore may help to guide rehabilitation. The aim of this study was thus to determine the spatiotemporal and kinematic parameters which were most related to the walking and turning sub-tasks of TUG performance in stroke patients.

Methods

29 stroke patients carried out the TUG test which was recorded using an optoelectronic system in two conditions: spontaneous and standardized condition (standardized foot position and instructed to turn towards the paretic side). They also underwent a clinical assessment. Stepwise regression was used to determine the parameters most related to Oriented gait and Turn sub-tasks. Relationships between explanatory parameters of Oriented gait and Turn performance and clinical scales were evaluated using Spearman correlations.

Results

Step length and cadence explained 82% to 95% of the variance for the walking sub-tasks in both conditions. Percentage single support phase and contralateral swing phase (depending on the condition) respectively explained 27% and 56% of the variance during the turning sub-task in the spontaneous and standardized conditions.

Discussion and Conclusion

Step length, cadence, percentage of paretic single support phase and non-paretic swing phase, as well as dynamic stability were the main parameters related to TUG performance and they should be targeted in rehabilitation.

Emotional influences on sit-to-walk in healthy young adults

The purpose of this study was to investigate influences of emotional feelings on sit-to-walk (STW). Eighteen healthy young adults performed STW while feeling sadness, anger, joy and neutral emotion. Emotions were elicited using an autobiographical memories task. We used an optoelectronic motion capture system to collect motion data and assessed kinematics of STW. Emotion-related differences in STW kinematics were consistent with differences in movement speed. Compared to neutral emotion, sadness was associated with increased STW duration and phase durations, decreased peak forward and vertical center-of-mass (COM) velocity, increased drop in forward COM velocity, and increased forward and vertical normalized jerk score (NJS). Anger and joy were associated with decreased STW duration and phase durations, increased peak forward and vertical COM velocity, decreased drop in forward COM velocity, and decreased forward and vertical NJS compared to neutral emotion. Findings suggest that emotional feelings affect movement speed, hesitation, and movement smoothness during STW.

Effects of Directional Change on Postural Adjustments during the Sit-to-walk Task

[Purpose] The purpose of this study was to clarify the effects of directional change on postural adjustments during the sit-to-walk (STW) task. [Subjects] Fifteen healthy young men participated in this study. [Methods] Subjects were required to stand up from a chair and walk toward a target. The first step was limited to the right limb only. Three conditions of target direction (straight, ipsilateral and contralateral) were set. For the ipsilateral and contralateral conditions, the target was placed at an angle 45° clockwise and 45° counterclockwise from straight ahead, respectively. Trials were recorded by a motion capture system and force plates. The forward momentum of the body, time of events, center of pressure (COP) and center of gravity (COG) displacement were measured and compared between conditions. [Results] In the contralateral condition, the fluidity index was significantly lower than that in the straight condition. In the contralateral condition, COP displacement toward the swing limb was larger than in the other conditions. [Conclusion] The present results indicate that a directional change during the STW task affects fluidity and postural adjustments. When the STW direction was changed to diagonal, the lateral component of postural control became more important.

Biomechanics of rising from a chair and walking in pregnant women

The present study aimed to assess the changes in the pattern of rising from a chair and walking forward as pregnancy progressed. Twelve pregnant women and 10 nulliparous women were included in this study. Participants were videotaped with a digital video camera in the sagittal plane, and the coordinates of the markers attached to the subjects were identified using image analysis software. The peak trunk-flexion angle in pregnant women during rising was smaller, but the hip-extension angle during the stance phase was larger than in controls. Also, the peak horizontal and vertical velocities of the center of mass were lower, and appeared earlier, in pregnant women than in controls. During rising, pregnant women dampened the propulsion attributable to increased uterus volume, and they enhanced the forward propulsion at gait initiation. To ensure safe motion, pregnant women should not initiate gait until reaching a stable standing position after rising.

Measuring movement fluency during the sit-to-walk task

BACKGROUND

Restoring movement fluency is a key focus for physical rehabilitation; it's measurement, however, lacks objectivity. The purpose of this study was to find whether measurable movement fluency variables differed between groups of adults with different movement abilities whilst performing the sit-to-walk (STW) movement. The movement fluency variables were: (1) hesitation during movement (reduction in forward velocity of the centre of mass; CoM), (2) coordination (percentage of temporal overlap of joint rotations) and (3) smoothness (number of inflections in the CoM jerk signal).

METHODS

Kinematic data previously collected for another study were extracted for three groups: older adults (n=18), older adults at risk of falling (OARF, n=18), and younger adults (n=20). Each subject performed the STW movement freely while a motion analysis system tracked 11 body segments. The fluency variables were derived from the processed kinematic data and tested for group variation using analysis of variance.

FINDINGS

All three variables showed statistically significant differences among the groups. Hesitation (F=15.11, p<0.001) was greatest in the OARF 47.5% (SD 18.0), compared to older adults 30.3% (SD 15.9) and younger adults 20.8% (SD 11.4). Co-ordination (F=44.88, p<0.001) was lowest for the OARF (6.93%, SD 10.99) compared to both the young (31.21%, SD 5.48) and old (26.24%, SD 5.84). Smoothness (F=35.96, p<0.001) was best in the younger adults, 18.3 (SD 5.2) inflections, compared to the old, 42.5 (SD 11.5) and OARF, 44.25 (SD 7.29).

INTERPRETATION

Hesitation, co-ordination and smoothness may be valid indicators of movement fluency in adults, with important consequences for research and clinical practice.

Impact of stroke on anterior-posterior force generation prior to seat-off during sit-to-walk

Force generation during sit-to-walk (STW) post-stroke is a poorly studied area, although STW is a common daily transfer giving rise to a risk of falling in persons with disability. The purpose of this study was to describe and compare strategies for anterior-posterior (AP) force generation prior to seat-off during the STW transfer in both subjects with stroke and in matched controls. During STW at self-selected speed, AP force data were collected by 4 force plates, beneath the buttocks and feet from eight subjects with stroke (>6 months after onset) and 8 matched controls. Subjects with post-stroke hemiparesis and matched controls generated a similar magnitude of total AP force impulses (F(1,71)=0.67; p=0.42) beneath buttocks and feet prior to seat-off during STW. However, there were significant group differences in AP force impulse generation beneath the stance buttock (i.e. the non-paretic buttock in the stroke group), with longer duration (F(1,71)=8.78; p<0.005), larger net AP impulse (F(1,71)=6.76; p<0.05) and larger braking impulse (F(1,71)=7.24; p<0.05) in the stroke group. The total braking impulse beneath buttocks and feet was about 4.5 times larger in the stroke group than in the control group (F(1,71)=8.84; p<0.005). An intra- and inter-limb dys-coordination with substantial use of braking impulses was demonstrated in the stroke group. This motor strategy differed markedly from the smooth force interaction in the control group. These results might be important in the development of treatment models related to locomotion post-stroke.

Medio-lateral stability of sit-to-walk performance in older individuals with and without fear of falling

Most falls in older people are due to loss of balance during everyday locomotion, e.g., when initiating walking from sitting; sit-to-walk (STW). It has been considered that the broader stride width in walking that is seen in many people with fear of falling (FoF) does not increase stability, but could be predictive of future falls because of increased medio-lateral (ML) velocity of the body centre of mass (CoM). This study was aimed to examine step-, velocity- and stability-related parameters, focusing on ML stability, in STW performance of people with and without FoF. Ten subjects with FoF and 10 matched controls, aged > or = 70 years, were included. Kinematic and kinetic data were collected in a laboratory. Stability parameters were calculated from a formula implying that the vertical projection of the CoM extrapolated by adding its velocity times a factor radicall/g (height of inverted pendulum divided by gravity) should fall within the base of support (BoS). A related spatial margin of stability (SMoS), defined as the minimum distance from the extrapolated CoM (XCoM) to the boundaries of the BoS, was also calculated. In the phase 'seat-off-second-toe-off', the FoF group had significantly (p<0.05) shorter and broader steps, lower forward but similar ML CoM velocity, and broader CoM and XCoM widths. The FoF group therefore exhibited a disproportionately large sideways velocity compared to the controls. This indicates that STW may be a hazardous transfer for older people with FoF, which should be relevant in assessment and training aimed at preventing falls.