Corinne G.C. Horlings

A weak balance: the contribution of muscle weakness to postural instability and falls

Muscle strength is a potentially important factor contributing to postural control. In this article, we consider the influence of muscle weakness on postural instability and falling. We searched the literature for research evaluating muscle weakness as a risk factor for falls in community-dwelling elderly individuals, for evidence that strength training reduces falls, and for pathophysiological evidence from patients with neuromuscular disease that supports the link between muscle weakness and falls. In virtually all studies that included strength testing, muscle weakness was a consistent risk factor for falls in the elderly. Studies that evaluated the merits of muscle strength training often showed a reduction in fall rates, particularly when strength training was a component of a multifactorial intervention, although it was unclear whether strength training alone led to a fall reduction. Surprisingly few studies addressed the pathophysiological relationship between muscle strength and balance control. We conclude that muscle weakness is an important risk factor for falls that is potentially amenable to therapeutic intervention, and that future studies should further clarify the role of muscle weakness in balance control and the pathophysiology of falls.

Effects of biofeedback on trunk sway during dual tasking in the healthy young and elderly

We examined the effect of biofeedback of trunk sway on balance control while walking and performing a simultaneous cognitive or motor task. Thirteen healthy elderly (mean age (+/-S.E.M.) 70.8+/-2.0 years) and 16 healthy young (mean age 21.5+/-0.7 years) subjects performed three gait tasks while wearing body-worn gyroscopes, mounted at L1-3, to measure trunk sway. The gait tasks were walking normally, walking and counting backwards in 7s, and walking while carrying a tray with cups of water. Differences in trunk sway were examined when subjects performed the gait tasks with or without a head mounted actuator system which provided subjects with vibro-tactile, auditory and visual biofeedback of trunk sway. In the young, trunk pitch (fore-aft) angles, and trunk roll (sideways) and pitch angular velocities were significantly reduced using biofeedback across all three gait tasks. In the elderly, the same angle and angular velocities were also significantly reduced while walking normally. During walking while carrying a tray, only trunk sway velocities were significantly reduced, whereas no improvements were seen for walking while counting backwards. Counting backwards ability significantly improved with feedback. Young participants were able to perform a dual task during gait and employ biofeedback to reduce trunk sway. Elderly participants were not able to reduce sway using biofeedback during the cognitive task but were able to reduce sway velocities with biofeedback during the motor task.

Influence of virtual reality on postural stability during movements of quiet stance

INTRODUCTION Balance problems during virtual reality (VR) have been mentioned in the literature but seldom investigated despite the increased use of VR systems as a training or rehabilitation tool. We examined the influence of VR on body sway under different stance conditions. METHODS Seventeen young subjects performed four tasks (standing with feet close together or tandem stance on firm and foam surfaces for 60s) under three visual conditions: eyes open without VR, eyes closed, or while viewing a virtual reality scene which moved with body movements. Angular velocity transducers mounted on the shoulder provided measures of body sway in the roll and pitch plane. RESULTS VR caused increased pitch and roll angles and angular velocities compared to EO. The effects of VR were, for the most part, indistinguishable from eyes closed conditions. Use of a foam surface increased sway compared to a firm surface under eyes closed and VR conditions. CONCLUSION During the movements of quiet stance, VR causes an increase in postural sway in amplitude similar to that caused by closing the eyes. This increased sway was present irrespective of stance surface, but was greatest on foam.

Vestibular and proprioceptive influences on trunk movements during quiet standing

We characterized upper trunk and pelvis motion in normal subjects and in subjects with vestibular or proprioceptive loss, to document upper body movement modes in the pitch and roll planes during quiet stance. Six bilateral vestibular loss (VL), six bilateral lower-leg proprioceptive loss (PL) and 28 healthy subjects performed four stance tasks: standing on firm or foam surface with eyes open or closed. Motion of the upper body was measured using two pairs of body-worn gyroscopes, one mounted at the pelvis and the other pair at the shoulders. Pitch and roll angular velocities recorded from the gyroscopes were analyzed separately for low-frequency (<0.7 Hz) and high-frequency (>3 Hz) motion. Low-frequency pitch motion was similar for all groups, consisting of in-phase pelvis and shoulder motion. High-frequency pitch motion in controls and VL subjects was dominated by pelvis motion with little shoulder motion, but vice versa in PL subjects. Low-frequency roll motion changed for all groups from mainly shoulder and little pelvis motion to in-phase pelvis and shoulder motion after moving from a firm to foam surface. In contrast, high-frequency roll motion changed from mainly shoulder motion to mainly pelvis motion with the change to a foam surface, except for PL subjects with eyes closed. Coherent low-frequency sway between pelvis and shoulder was only pronounced in VL patients. These results indicate that relative motion between the pelvis and shoulder depends on the support surface, the type of sensory loss, and whether the motion is in roll or pitch plane. Furthermore, relative motion between the pelvis and upper trunk is an integral part of movement modes used to control quiet stance. Vestibular loss patients showed very similar movement modes as controls, with larger amplitudes. Proprioceptive loss patients, however, used more shoulder motion and stabilized the pelvis for the high-frequency mode. We conclude that there is relative motion between the upper trunk and pelvis during quiet stance and suggest that it may contribute to balance control.

Directional effects of biofeedback on trunk sway during gait tasks in healthy young subjects

Biofeedback of trunk sway is a possible remedy for patients with balance disorders. Because these patients have a tendency to fall more in one direction, we investigated whether biofeedback has a directional effect on trunk sway during gait. Forty healthy young participants (mean age 23.1 years) performed 10 gait tasks with and without biofeedback. Combined vibrotactile, auditory and visual feedback on trunk sway in either the lateral or anterior-posterior (AP) direction was provided by a head-mounted actuator system. Trunk roll and pitch angles, calculated from trunk angular velocities measured with gyroscopes, were used to drive the feedback. A reduction in sway velocities occurred across all tasks regardless of feedback direction. Reductions in sway angles depended on the task. Generally, reductions were greater in pitch. For walking up and down stairs, or over barriers, pitch angle reductions were greater with AP than lateral feedback. For tandem and normal walking, reductions were similar in pitch and roll angles for both feedback directions. For walking while rotating or pitching the head or with eyes closed, only pitch angle was reduced for both feedback directions. These results indicate that the central nervous system is able to incorporate biofeedback of trunk sway from either the AP or lateral direction to achieve a reduction in both pitch and roll sway. Greater reductions in pitch suggest a greater ability to use this direction of trunk sway biofeedback during gait.

The influence of walking speed and gender on trunk sway for the healthy young and older adults

SIR—Falls are a major problem for the elderly and others prone to fall [1–7], occurring frequently during walking [8, 9]. Maki et al. [10] suggested that the ‘cautious’ gait pattern, characterised by reduced walking speed and shortened step length, is adopted by older people to minimise the risk of falling. Somewhat paradoxically, these changes may predispose to trips and slips [11, 12]. Step width and length are influenced by walking speed [13]. It is difficult, however, to define stability during walking with thesemeasures. Trunk swaymay provide alternativemeasures as increased trunk sway is associated with an increased risk of falling [13–15]. Increased trunk sway occurs in the young when they walk slower or faster than normal [13], indicating that preferred walking speed is the most stable. A different conclusion was reached for older persons who show reduced sway velocities and angles with slower walking speeds [14]. Greater variability in trunk roll and pitch angle was observed at all speeds for older adults compared to younger people [16]. However, the effect of speed, on the amplitudes of trunk roll (side-to-side) and pitch (fore–aft) angle and angular velocity for both groups, has not been reported. In addition, there is a gender difference between the walking styles and the gait parameters [17–24], possibly for trunk sway too, at different walking speeds. In order to provide more complete data, the current study investigated the influence of age, gender and walking speed on balance measures in the form of trunk sway angles and velocities. It was hypothesised that these measures increase across walking speeds for both young and older people with larger values for the elderly. This hypothesis was verified except that trunk sway angles were not less for slower walking speeds than the preferred.

Differentiating malingering balance disorder patients from healthy controls, compensated unilateral vestibular loss, and whiplash patients using stance and gait posturography.

Differentiating balance disorder patients who are malingering from those with organic balance disorders is difficult and costly. We used trunk sway measured during several stance and gait tasks in 18 patients suspected of malingering in order to differentiate these from 20 patients who had suffered unilateral vestibular loss 3 months earlier, 20 patients with documented whiplash injuries, and 34 healthy controls. Classification results ranged from 72 to 96% and were equally accurate for task or criteria variables based on 90% sway values. The tasks yielding the best discrimination were: standing with eyes closed on a foam and firm surface; standing with eyes open on a firm surface; standing on 1 leg; and walking tandem steps. The criteria yielding the best discrimination were: standing with eyes open on a firm surface; the difference between standing with eyes closed on foam and firm surfaces; the difference between walking tandem steps and standing on 1 leg with eyes open; and the difference between roll and pitch velocity when walking 8 tandem steps. We conclude that discriminating suspected malingering balance disorder patients is possible using variables or criteria based on objective measures of trunk sway during several stance and gait tasks.

Incorporating voluntary unilateral knee flexion into balance corrections elicited by multi-directional perturbations to stance.

Positive effects on lateral center of mass (CoM) shifts during balance recovery have been seen with voluntarily unilateral arm raising but not with voluntarily bilateral knee flexion. To determine whether unilateral voluntary knee movements can be effectively incorporated into balance corrections we perturbed the balance of 30 young healthy subjects using multi-directional rotations of the support surface while they simultaneously executed unilateral knee flexion. Combined pitch and roll rotations (7.5 degrees and 60 degrees/s) were presented randomly in six different directions. Subjects were tested in four stance conditions: balance perturbation only (PO); cued flexion of one knee only (KO); combined support surface rotation and cued (at rotation onset) flexion of the uphill knee, contralateral to tilt (CONT), or of the downhill knee, ipsilateral to tilt (IPS). Outcome measures were CoM motion and biomechanical and electromyography (EMG) responses of the legs, arms and trunk. Predicted measures (PO+KO) were compared with combined measures (CONT or IPS). Unilateral knee flexion of the uphill knee (CONT) provided considerable benefit in balance recovery. Subjects rotated their pelvis more to the uphill side than predicted. Downhill knee bending (IPS) also had a positive effect on CoM motion because of a greater than predicted simultaneous lateral shift of the pelvis uphill. KO leg muscle activity showed anticipatory postural activity (APA) with similar profiles to early balance correcting responses. Onsets of muscle responses and knee velocities were earlier for PO, CONT, and IPS compared to KO conditions. EMG response amplitudes for CONT and IPS conditions were generally not different from the PO condition and therefore smaller than predicted. Later stabilizing responses at 400 ms had activation amplitudes generally equal to those predicted from the PO+KO conditions. Our results suggest that because EMG patterns of anticipatory postural activity of voluntary unilateral knee flexion and early balance corrections have similar profiles, the CNS is easily able to incorporate voluntary activation associated with unilateral knee flexion into automatic postural responses. Furthermore, the effect on movement strategies appears to be non-linear. These findings may have important implications for the rehabilitation of balance deficits.

Adding quantitative muscle MRI to the FSHD clinical trial toolbox

Objective: To add quantitative muscle MRI to the clinical trial toolbox for facioscapulohumeral muscular dystrophy (FSHD) by correlating it to clinical outcome measures in a large cohort of genetically and clinically well-characterized patients with FSHD comprising the entire clinical spectrum. Methods: Quantitative MRI scans of leg muscles of 140 patients with FSHD1 and FSHD2 were assessed for fatty infiltration and TIRM hyperintensities and were correlated to multiple clinical outcome measures. Results: The mean fat fraction of the total leg musculature correlated highly with the motor function measure, FSHD clinical score, Ricci score, and 6-minute walking test (correlation coefficients −0.845, 0.835, 0.791, −0.701, respectively). Fat fraction per muscle group correlated well with corresponding muscle strength (correlation coefficients up to −0.82). The hamstring muscles, adductor muscles, rectus femoris, and gastrocnemius medialis were affected most frequently, also in early stage disease and in patients without leg muscle weakness. Muscle involvement was asymmetric in 20% of all muscle pairs and fatty infiltration within muscles showed a decrease from distal to proximal of 3.9%. TIRM hyperintense areas, suggesting inflammation, were found in 3.5% of all muscles, with and without fatty infiltration. Conclusions: We show a strong correlation between quantitative muscle MRI and clinical outcome measures. Muscle MRI is able to detect muscle pathology before clinical involvement of the leg muscles. This indicates that quantitative leg muscle MRI is a promising biomarker that captures disease severity and motor functioning and can thus be included in the FSHD trial toolbox.

The epidemiology of neuromuscular disorders: Age at onset and gender in the Netherlands

Based on approximately eight years of data collection with the nationwide Computer Registry of All Myopathies and Polyneuropathies (CRAMP) in the Netherlands, recent epidemiologic information for thirty neuromuscular disorders is presented. This overview includes age and gender data for a number of neuromuscular disorders that are either relatively frequently seen in the neuromuscular clinic, or have a particular phenotype. Since 2004, over 20,000 individuals with a neuromuscular disorder were registered in CRAMP; 56% men and 44% women. The number per diagnosis varied from nine persons with Emery-Dreifuss muscular dystrophy to 2057 persons with amyotrophic lateral sclerosis. Proportions of men ranged from 38% with post-polio syndrome to 68% with progressive spinal muscular atrophy, excluding X-chromosome linked disorders. Inclusion body myositis showed the highest median age at diagnosis of 70 years. These data may be helpful in the diagnostic process in clinical practice and trial readiness.