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.

Temporal coordination of the sit-to-walk task in subjects with stroke and in controls.

OBJECTIVES: To explore events and describe phases for temporal coordination of the sit-to-walk (STW) task, within a semistandardized set up, in subjects with stroke and matched controls. In addition, to assess variability of STW phase duration and to compare the relative duration of STW phases between the 2 groups. DESIGN: Cross-sectional. SETTING: Research laboratory. PARTICIPANTS: A convenience sample of persons with hemiparesis (n=10; age 50-67y) more than 6 months after stroke and 10 controls matched for sex, age, height, and body mass index. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Relative duration of STW phases, SE of measurement in percentage of the mean, and intraclass correlation coefficients (ICCs). RESULTS: Four STW phases were defined: rise preparation, transition, primary gait initiation, and secondary gait initiation. The subjects with stroke needed 54% more time to complete the STW task than the controls did. ICCs ranged from .38 to .66 and .22 to .57 in the stroke and control groups, respectively. SEs of measurement in percentage of the mean values were high, particularly in the transition phase: 54.1% (stroke) and 50.4% (controls). The generalized linear model demonstrated that the relative duration of the transition phase was significantly longer in the stroke group. CONCLUSIONS: The present results extend existing knowledge by presenting 4 new phases of temporal coordination of STW, within a semistandardized set-up, in persons with stroke and in controls. The high degree of variability regarding relative STW phase duration was probably a result of both the semistandardized set up and biological variability. The significant difference in the transition phase across the 2 groups requires further study.

Seat load characteristics in children with neuromuscular and syndrome-related scoliosis: effects of pathology and treatment.

The amount of correction from spine deformity surgery that is required to avoid asymmetric and unbalanced sitting is not known, and methods sensitive enough to document moderate changes in pressure distribution over time are few, as the commonly used methods are qualitative or semiquantitative. The aim was to analyse seating pressure distribution with a pressure sensor mat system in patients with nonidiopathic scoliosis and to compare the pressure distribution with that in able-bodied controls. The aim was also to apply the method in a surgically treated scoliosis group before and after the spine fusion. Peak pressure, contact area of the entire and the maximum pressure surface, and three measures of asymmetry were calculated. Patients had higher peak pressure and more asymmetric loading than controls. Significant difference was indicated in contact area. After the spine fusion, all asymmetry indices improved. The method fulfilled clinical needs to detect the differences from normal controls as well as the surgery-dependent changes.

Reach performance and postural adjustments during standing in children with severe spastic diplegia using dynamic ankle-foot orthoses.

OBJECTIVE: To investigate the co-ordination between reaching, ground reaction forces and muscle activity in standing children with severe spastic diplegia wearing dynamic ankle-foot orthoses compared with typically developing children. DESIGN: Clinical experimental study. SUBJECTS: Six children with spastic diplegia (Gross Motor Function Classification System level III-IV) and 6 controls. METHODS: Ground reaction forces (AMTI force plates), ankle muscle activity (electromyography and displacement of the hand (ELITE systems) were investigated while reaching for an object. RESULTS: For the children with severe spastic diplegia who were wearing dynamic ankle-foot orthoses, co-ordination between upward and forward reach velocity differed regarding the temporal sequencing and amplitude of velocity peaks. During reaching, these children lacked interplay of pushing force beneath the reach leg and braking force beneath the non-reach leg and co-ordinated ankle muscle activity, compared with controls. CONCLUSION: The results suggest differences in reach performance and postural adjustments for balance control during a reaching movement in standing between children with spastic diplegia Gross Motor Function Classification System level III-IV, wearing dynamic ankle-foot orthoses compared with typically developing children.

Motor control of every day motor tasks: guidance for neurological rehabilitation.

This paper reports some of the research activities conducted at the Motor Control and Physical Therapy Laboratory aimed to understand the control of the coordination between posture and voluntary actions as reflected in the performance of everyday motor tasks in subject with normal and impaired motor control. Through multi-factorial analysis regarding the kinematics, ground reaction forces and muscle activity patterns (EMG), motor control variables critical for specific task performance are identified. Target-reaching in subjects after stroke and in children with cerebral palsy are discussed in some detail. Further, transfer skills in subjects with spinal cord injury as well as weight shift during gait initiation in young and elderly adults and during clinical balance testing are presented. The research findings are illuminated with respect to clinical implications in neurological rehabilitation, based on the motor control hypothesis.

Age-related differences in postural adjustments in connection with different tasks involving weight transfer while standing.

Weight transfer designed to change the area of the supportive base during the performance of three different motor tasks (one-leg stance, tandem stance and gait initiation) was examined both in healthy, physically active elderly people and younger adults. The former two tasks are balance tests used clinically. Our hypothesis was that the elderly subjects would demonstrate age-related changes in their postural adjustments that could be detected by analysis of the ground reaction forces. While 24 healthy elderly adults (65-77 years of age) and 26 younger adults (24-40 years of age) performed these three tasks, the ground reaction forces were recorded from two force plates. Prior to the onset of all three tasks, the elderly placed significantly more weight on the leg that was to provide support (the stance leg), than did the younger individuals. The analyses revealed two distinct phases of weight transfer, i.e., an initial thrust and a subsequent unloading phase. The elderly individuals exhibited a significantly longer unloading phase, as well as a higher frequency of peaks of vertical and lateral forces during this phase. Moreover, the maximal force rate during this phase was achieved at an earlier time point by the elderly. However, both groups generated forces of similar magnitudes and force rates. In conclusion, our findings indicate the presence of age-related differences in the temporal phasing of the ground reaction forces in all three of these tasks involving weight transfer, whereas the magnitude and rates of change of these forces are independent of age.

Associated sagittal spinal movements in performance of head pro- and retraction in healthy women: a kinematic analysis.

Sagittal head excursions are frequently used as diagnostic and treatment tools by physiotherapists. Retractions are performed to promote good head-on-body orientation. This study examined the regional contribution of spinal movements to head pro- and retraction in addition to the effect of a more or less restrained sitting position in healthy women. Fourteen healthy women performed seven sagittal head excursions in a more or less restrained sitting position, during which time their kinematic response was measured with an optoelectronic system. Total anterior/posterior head excursion was smaller (P=0.005) in the more restrained sitting position. In both sitting positions, approximately 60% of the total anterior/posterior head excursion originated from the cervical spine, almost 30% from the cervicothoracic spine C7-T4, and approximately 10% from thoracic regions down to T12. Middle thoracic vertical displacement was smaller (p=0.005) in the more restrained sitting position. A high correlation was found between total head excursion and the cervicothoracic unit displacements in both sitting positions (r=0.79, r=0.85, respectively). In each sitting position, the craniovertebral angle, and the tragus-C7-horizontal line decreased in protraction. Movements in the thoracic region contributed to the total head excursion. Therefore, clinicians should recognize the thoracic contribution to sagittal head excursion when using pro- and retraction as a diagnostic and treatment tool.

Physically active older adults display alterations in gait initiation.

An understanding of age-related changes in motor behaviour is important when considering the design of training programs for fall-prevention in the elderly. Gait initiation is a phase of walking during which falls are often provoked and this study compares strategies employed by healthy older and young adults during gait initiation. Twenty-nine older, physically active subjects (65-79 years) and 28 younger individuals (23-40 years) were instructed to cross a staged road, when a traffic light changed from red to green, leading with a freely chosen or predetermined leg. Electromyography of tibialis anterior (TA) and lateral gastrocnemius (LG) muscles, ground reaction forces exerted and step lengths were recorded. The elderly displayed several striking differences compared to the young individuals. Weight bearing during initial standing was considerably more unequal and reaction time was 46% longer, with identical duration of gait initiation. Swing leg peak posterior force (% BW) tended to be smaller, but the increase of vertical force was larger. Eight elderly and one young subject lacked anticipatory TA onset; however TA anticipation increased with trial number in the elderly group. When the starting leg was predetermined, the deficiency in TA anticipation was no longer apparent. In the stance leg all forces were smaller and LG was recruited later, and unlike the young subjects generally after the swing leg had left the ground. The results revealed that ageing leads to significant alterations in weight bearing and ankle muscle activation in relation to gait initiation. Gait initiation changed significantly when the starting leg was predetermined and, in the elderly, with repetition.

Postural steadiness and weight distribution during tandem stance in healthy young and elderly adults.

BACKGROUND: Tandem stance is a clinical measure of standing balance considered to assess postural steadiness in a heel-to-toe position by a temporal measurement. To our knowledge, no studies have evaluated the change of postural steadiness, expressed as force variability, over time. The objective of this paper is to investigate postural steadiness during 30 s of tandem stance in healthy elderly and young adults, and to explore the weight distribution between legs during tandem stance. METHODS: A cross-sectional analysis comparing ground reaction forces and muscle activity in 26 healthy elderly adults (mean age 70.6 years) and 27 healthy young adults (mean age 30.0 years). Ground reaction forces beneath both feet and muscle activity of ankle muscles were recorded while the subjects performed 30 s of tandem stance during two conditions. FINDINGS: Two phases were identified in both groups: First a dynamic phase, a decrease in force variability during the first 3-4 s after foot placement, and thereafter a static phase, maintaining a certain level of force variability. Age-related changes were seen in the decrease in force variability (P<0.001) and ankle muscle activity (P<0.001). However, both groups placed more weight on the rear leg (P<0.001). INTERPRETATION: The first few seconds of tandem stance pose the greatest challenge to postural steadiness and influence the static phase. We suggest that the dynamic phase is the most crucial period of time for assessing balance requirements. Independent of age, tandem stance is not a task for equal weight bearing.

One-leg stance in healthy young and elderly adults: a measure of postural steadiness?

OBJECTIVE: To investigate postural steadiness during 30 s of one-leg stance in healthy young and elderly adults, by analysing the pattern of the ground reaction force variability. DESIGN: A laboratory set-up was used to analyse the variability of the ground reaction forces in relation to time as a measure of postural steadiness. BACKGROUND: The one-leg stance test is a measure considered to assess postural steadiness in a static position by a temporal measurement. The common notion is that a better postural steadiness, i.e. less force variability, allows for longer time standing on one leg. However, there is lack of evidence how postural steadiness during one-leg stance changes over time. METHODS: Twenty-eight healthy elderly and 28 healthy young adults were tested by means of force plates assessing ground reaction forces while performing one-leg stance. RESULTS: During one-leg stance, two phases could be identified in both groups: First a dynamic phase, a rapid decrease of force variability, and thereafter a static phase, maintaining a certain level of force variability. During the first 5 s of one-leg stance the force variability decreased significantly more in the young group resulting in a lower force variability level during the static phase than in the elderly. CONCLUSIONS: The difficulties in maintaining the static position in elderly seems dependent on the reduced initial decrease in force variability and/or musculoskeletal components. We suggest that the first 5 s are crucial when assessing balance during one-leg stance.

Does the functional reach test reflect stability limits in elderly people?

OBJECTIVE: To explore how the Functional Reach test correlates with the displacement of the centre of pressure and whether the test is a measure of the stability limits in healthy elderly people. Also to explore the performance parameters during the Functional Reach test. DESIGN: Method comparison study. SUBJECTS: Twenty-seven healthy elderly subjects. METHODS: Whole body kinematics (ELITE systems), ground reaction forces (AMTI) and muscle activity (EMG) parallel with clinical yardstick measure while performing the Functional Reach test. RESULTS: This study showed a low correlation (r = 0.38) between reach distance and displacement of centre of pressure and a moderate correlation (r = 0.68) between forward rotation of the trunk and reach distance. The movement during the Functional Reach test was characterized by a large forward rotation of the trunk and a small extension in the ankle. The latter constraining centre of pressure forward displacement. CONCLUSIONS: The results suggest that the Functional Reach test is a weak measure of the stability limits. Movement of the trunk seems to influence the test more than the displacement of the centre of pressure. When using the Functional Reach test for assessing balance, compensatory mechanisms should be taken into account.

Joint coordination during whole-body lifting in women with low back pain after pregnancy.

OBJECTIVE: To quantify differences in the kinematics of lifting between women with low back and/or pelvic pain after pregnancy and women without. DESIGN: Comparison study. SETTING: Research laboratory. PARTICIPANTS: Volunteer sample of 7 women with pain (positive pain drawing, no physical examination) and 9 female controls (not matched). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Duration of downward and upward phases, relative instant of box lift-off, joint angles, spatial angles of trunk and pelvis, pelvic angle relative to trunk, and phase angle relationships between joints. RESULTS: The duration of the upward phase +/- standard deviation was longer in the pain group (1731+/-290 ms vs 1489+/-187 ms, P=.031). At box lift-off, this group had less hip joint flexion (101.9 degrees +/-20.8 degrees vs 78.7 degrees +/-12.4 degrees, P=.015) but more backward pelvis tilt relative to the trunk, that is, more lumbar spine flexion (126.3 degrees +/-16.8 degrees vs 109.0 degrees +/-12.3 degrees, P=.031). The pain group showed an immediate transition from lumbar spine flexion to extension, whereas the controls maintained peak flexion for about 600 ms. The peak phase lag between knee and hip joint extension in the upward phase was larger for the pain group (-29.7 degrees +/-8.3 degrees vs -17.2 degrees +/-5.5 degrees, P=.003). CONCLUSION: Women with low back and/or pelvic pain after pregnancy showed different kinematics of lifting. Further research is needed to determine the exact relationship between the altered kinematics and the underlying disorder.