Responses of Ankle Musculature of Healthy Subjects and Hemiplegic Patients to Sinusoidal Anterior-Posterior Movements of the Base of Support

Pain alleviation improves balance control and muscular coordination of lower limbs in patients with chronic ankle instability during sinusoidal perturbations

BACKGROUND

It is well established that individuals with chronic ankle instability manifest deficits in balance control and muscle activation. Given the prevalence of pain as a prominent symptom in this population, there is a need for in-depth investigation of its role in contributing to these impairments.

METHODS

A Stewart platform was used to generate translational sinusoidal perturbations in the antero-posterior direction. Eighteen individuals with chronic ankle instability and concurrent ankle pain were recruited. They were instructed to assume a central stance on the support surface with open eyes both before and 30 min after local analgesia. Data of center of pressure and electromyography of the tibialis anterior and medial gastrocnemius were recorded. Statistical analysis was performed to make comparisons pre- and post-analgesia using two-tailed paired t-test for the continuous variables.

FINDINGS

Pain intensity was significantly decreased after local anesthetic injections. Antero-posterior center of pressure parameters significantly decreased following the injection. Also, there was an increase in the regularity of the center of pressure pattern. The electromyographic pattern of the tibialis anterior and medial gastrocnemius exhibited various activation patterns. After pain alleviation, the characteristic electromyographic response of the tibialis anterior and medial gastrocnemius was reciprocal contraction and relaxation that corresponded with the sinusoidal pattern of the perturbations.

INTERPRETATION

Individuals who had chronic ankle instability and ankle pain demonstrated impaired balance control during sinusoidal perturbations. Mitigating pain improved their balance performance, evident in the center of pressure pattern and the coordination of lower limb muscles.

Posterior fall-recovery training applied to individuals with chronic stroke: A single-group intervention study

BACKGROUND

To assess the effects of the initial stepping limb on posterior fall recovery in individuals with chronic stroke, as well as to determine the benefits of fall-recovery training on these outcomes.

METHODS

This was a single-group intervention study of 13 individuals with chronic stroke. Participants performed up to six training sessions, each including progressively challenging, treadmill-induced perturbations from a standing position. Progressions focused on initial steps with the paretic or non-paretic limb. The highest perturbation level achieved, the proportion of successful recoveries, step and trunk kinematics, as well as stance-limb muscle activation about the ankle were compared between the initial stepping limbs in the first session. Limb-specific outcomes were also compared between the first and last training sessions.

FINDINGS

In the first session, initial steps with the non-paretic limb were associated with a higher proportion of success and larger perturbations than steps with the paretic limb (p = 0.02, Cohen's d = 0.8). Paretic-limb steps were wider relative to the center of mass (CoM; p = 0.01, d = 1.3), likely due to an initial standing position with the CoM closer to the non-paretic limb (p = 0.01, d = 1.4). In the last training session, participants recovered from a higher proportion of perturbations and advanced to larger perturbations (p < 0.05, d > 0.6). There were no notable changes in kinematic or electromyography variables with training (p > 0.07, d < 0.5).

INTERPRETATION

The skill of posterior stepping in response to a perturbation can be improved with practice in those with chronic stroke, we were not able to identify consistent underlying kinematic mechanisms behind this adaptation.

Impact of Spasticity on Balance Control during Quiet Standing in Persons after Stroke

Background

Balance impairments, falls, and spasticity are common after stroke, but the effect of spasticity on balance control after stroke is not well understood.

Methods

In this cross-sectional study, twenty-seven participants with stroke were divided into two groups, based on ankle plantar flexor spasticity level. Fifteen individuals with high spasticity (Modified Ashworth Scale (MAS) score of ≥2) and 12 individuals with low spasticity (MAS score <2) completed quiet standing trials with eyes open and closed conditions. Balance control measures included centre of pressure (COP) root mean square (RMS), COP velocity, and COP mean power frequency (MPF) in anterior-posterior and mediolateral (ML) directions. Trunk sway was estimated using a wearable inertial measurement unit to measure trunk angle, trunk velocity, and trunk velocity frequency amplitude in pitch and roll directions.

Results

The high spasticity group demonstrated greater ML COP velocity, trunk roll velocity, trunk roll velocity frequency amplitude at 3.7 Hz, and trunk roll velocity frequency amplitude at 4.9 Hz, particularly in the eyes closed condition (spasticity by vision interaction). ML COP MPF was greater in the high spasticity group.

Conclusion

Individuals with high spasticity after stroke demonstrated greater impairment of balance control in the frontal plane, which was exacerbated when vision was removed.

Ordinal and timed balance measurements: reliability and validity in patients with stroke

The aim of this study of 38 patients with stroke was to describe the intrasession and intersession reliability and validity of ordinally graded and timed balance tests. Patients had a mean age and time since stroke of 67 years and 21 days respectively. Balance and gait were both timed with a stop-watch and given an ordinal score. Balance was timed for four different task levels: feet apart, feet together and unilateral stance (either limb first). Subjects who demonstrated the ability to complete the task for 60 seconds proceeded to the next, more difficult, task level. Most subjects remained within an ordinal balance category during a session; 81.6% for session 1 and 86.8% for session 2. The distribution of ordinal balance scores between sessions revealed that 31 of the 38 subjects remained within the same ordinal balance score, with the remainder of subjects scoring higher during session 2. The weighted Kappa coefficient for these scores was 0.858, indicating excellent reliability. The magnitude of the intrasession and intersession intraclass correlation coefficients for unilateral balance times indicated acceptable reliability. The Spearman correlations showed that balance measurements were a valid indicator of walking performance regardless of whether timed or ordinal measurements were used to characterize balance and gait. Given the findings of this study relevant to reliability and validity, the use of the more precise timed balance times cannot be advocated.

Automatic and voluntary lateral weight shifts in rehabilitation of hemiparetic patients

One of the main objectives of exercise therapy for hemiparetic patients is the rehabilitation of their impaired ability to accept and bear bodyweight on the involved lower extremity. The purpose of this study was to compare two types of therapeutic exercises, automatic and voluntary weight shifts, used as treatment for this problem.

Thirteen hemiparetic patients and nine age-matched healthy controls participated in the study. Criterion variables were four: (1) body sway; (2) location of the centre of pressure; (3) activation pattern of the gluteus medius and medial gastrocnemius muscles; and (4) magnitude of activation of these two muscles. Each subject was tested three times: (1) during static stance; (2) while standing on a moving platform that imposed automatic lateral weight shifts; and (3) while standing on a stationary base and voluntarily shifting bodyweight from one lower limb to the other. Values of sway and location of the centre of pressure on the mediolateral axis were collected by the Chattecx balance system; magnitude and modulation of the muscular activity in both lower extremities were recorded with surface electromyography.

The findings showed significant differences between patients and controls in all four variables. Regarding differences between exercise modes, the main finding pointed to larger sways in voluntary as compared to automatic weight shifts. Presumably, body fixation during automatic perturbations was manifested in a decreased body sway. Stance symmetry and the EMG activation profile of the paretic muscles were not improved by either exercise mode.

Compensatory stepping responses in individuals with stroke: a pilot study

Impaired postural control and a high incidence of falls are commonly observed following stroke. Compensatory stepping responses are critical to reactive balance control. We hypothesize that, following a stroke, individuals with unilateral limb dyscontrol will be faced with the unique challenge of controlling such rapid stepping reactions that may eventually be linked to the high rate of falling. The objectives of this exploratory pilot study were to investigate compensatory stepping in individuals poststroke with regard to: (1) choice of initial stepping limb (paretic or non-paretic); (2) step characteristics; and (3) differences in step characteristics when the initial step is taken with the paretic vs. the non-paretic limb. Four subjects following stroke (38-165 days post) and 11 healthy young adults were recruited. Anterior and posterior perturbations were delivered by using a weight drop system. Force plates recorded centre-of-pressure excursion prior to the onset of stepping and step timing. Of the four subjects, three only attempted to step with their non-paretic limb and one stepped with either limb. Time to foot-off was generally slow, whereas step onset time and swing time were comparable to healthy controls. Two of the four subjects executed multistep responses in every trial, and attempts to force stepping with the paretic limb were unsuccessful in three of the four subjects. Despite high clinical balance scores, these individuals with stroke demonstrated impaired compensatory stepping responses, suggesting that current clinical evaluations might not accurately reflect reactive balance control in this population.

A review of standing balance recovery from stroke

Recently, interest in the mechanisms underlying balance recovery following stroke has grown, because insight into these mechanisms is necessary to develop effective rehabilitation strategies for different types of stroke. Studies dealing with the recovery of standing balance from stroke are, however, limited to rehabilitation inpatients with a unilateral supratentorial brain infarction or haemorrhage. In most of these patients, stance stability improves in both planes as well as the ability to compensate for external and internal body perturbations and to control posture voluntarily. Although there is evidence of true physiological recovery of paretic leg muscle functions in postural control, particularly during the first three months post-stroke, substantial balance recovery also occurs in patients when there are no clear signs of improved support functions or equilibrium reactions exerted through the paretic leg. This type of recovery probably takes much longer than 3 months. Apparently, mechanisms other than the restoration of paretic leg muscle functions may determine the standing balance recovery in patients after severe stroke. No information is available about the role of stepping responses as an alternative to equilibrium reactions for restoring the ability to maintain upright stance after stroke. The finding that brain lesions involving particularly the parieto-temporal junction are associated with poor postural control, suggests that normal sensory integration is critical for balance recovery. Despite a considerable number of intervention studies, no definitive conclusions can be drawn about the best approach to facilitate the natural recovery of standing balance following stroke.

Changing patterns of postural hip muscle activity during recovery from stroke

OBJECTIVE

To describe the recovery of neurophysiological responses to perturbation of standing balance after stroke.

METHODS

Surface electromyography (EMG) from hip abductors and adductors and ground reaction forces (GRF) were measured in response to 20 sideways pushes applied to the pelvis by a linear motor. Each subject's data from pushes in each direction were averaged and the presence of a muscle EMG response was assessed visually.

SUBJECTS

Thirteen acute hemiplegic patients were tested as soon as they could stand after stroke (median six weeks) and serially during recovery.

RESULTS

Four patterns of hip muscle activity were seen: (1) no response at all, (2) no response in hemiparetic muscles but compensation by contralateral muscles, (3) an appropriate, if delayed, response in the hemiparetic abductor but not adductor muscles, and (4) a relatively normal pattern in both hemiparetic muscles. Nine of 13 patients showed a change in pattern of hip muscle activity during recovery. All patients who initially resisted the sideways pushes solely with muscles of the unaffected leg later regained use of the hemiparetic hip abductors.

CONCLUSIONS

The pattern of hip muscle activation changed towards normal during recovery from stroke in most patients. Use of compensatory strategies early after stroke in these subjects did not prevent return of normal patterns of muscle activation later.