Muscle weakness impairs the proprioceptive control of human standing

Bed rest impairs the vestibular control of balance

Prolonged bed rest impairs standing balance but the underlying mechanisms are uncertain. Previous research suggests strength loss is not the cause, leaving impaired sensorimotor control as an alternative. Here we examine vestibular control of posture in 18 male volunteers before and after 60 days of bed rest. Stochastic vestibular stimulation (SVS) was used to evoke sway responses before, 1 and 6 days after bed rest under different head yaw orientations. The directional accuracy and precision of these responses were calculated from ground reaction force vectors. Bed rest caused up to 63% increases in spontaneous standing sway and 31% reductions in leg strength, changes which were uncorrelated. The increase in sway was exacerbated when the eyes were closed. Mean directions of SVS-evoked sway responses were unaffected, being directed towards the anodal ear and rotating in line with head orientation in the same way before and after bed rest. However, individual trial analysis revealed 25%-30% increases in directional variability, which were significantly correlated with the increase in spontaneous sway (r = 0.48-0.71; P ≤ 0.044) and were still elevated on day 6 post-bed rest. This reveals that individual sway responses may be inappropriately oriented, a finding masked by the averaging process. Our results confirm that impaired balance following prolonged bedrest is not related to loss of strength. Rather, they demonstrate that the sensorimotor transformation process which converts vestibular feedback into appropriately directed balance responses is impaired. KEY POINTS: Prolonged inactivity impairs balance but previous research suggests this is not caused by loss of strength. Here we investigated vestibular control of balance before and after 60 days of bed rest using electrical vestibular stimulation (EVS) to evoke sway responses. Spontaneous sway significantly increased and muscle strength reduced following bed rest, but, in keeping with previous research, these two effects were not correlated. While the overall accuracy of EVS-evoked sway responses was unaffected, their directional variability significantly increased following bed rest, and this was correlated with the increases in spontaneous sway. We have shown that the ability to transform head-centred vestibular feedback into an appropriately directed body sway response is negatively affected by prolonged inactivity; this may contribute to the impaired balance commonly observed following bed rest.

Vibration perception among children and adolescents with Charcot-Marie-tooth disease and implications for foot posture

BACKGROUND

Alterations in vibration perception among children and adolescents with Charcot-Marie-Tooth disease might explain observed changes in foot posture. Therefore, this cross-sectional study compared the vibration perception of the lower limbs in youths with and without Charcot-Marie-Tooth disease and verified the cut-off value of the distal vibration perception for the Charcot-Marie-Tooth group. In addition, associations between dynamic plantar pressure, vibration perception and isometric muscle strength were investigated.

METHODS

Participants aged 9-18 (Charcot-Marie-Tooth group n = 32; Typical group n = 32) had vibration perception measured by a 128-Hz graduated tuning fork. The static and dynamic foot posture were evaluated by the Foot Posture Index and pressure distribution measuring system, respectively. For the Charcot-Marie-Tooth group, a hand-held dynamometer evaluated the isometric muscle strength of the lower limbs.

FINDINGS

Children with Charcot-Marie-Tooth disease presented impaired vibration perception at the distal phalanx of the hallux and head of the first metatarsal compared to their typically developing peers, while adolescents with Charcot-Marie-Tooth disease showed impairment in all the tested regions compared to their typically developing peers. The cut-off value for vibration perception for participants with Charcot-Marie-Tooth disease was 5.7, considering the original grade of the tuning-fork 128 Hz. Among the associations established for the Charcot-Marie-Tooth group, a greater vibration perception at the distal phalanx of the hallux was associated with a longer rearfoot contact time (β = 31.02, p = 0.04).

INTERPRETATION

These new findings may guide the clinical evaluation and rehabilitation treatment for children and adolescents with Charcot-Marie-Tooth disease.

Effect of Moving Tactile Stimuli to Mimic Altered Weight Distribution During Gait on Quiet Stance Body Sway

Our purpose in the present study was to examine whether moving tactile stimuli to the sole to mimic moving weight distribution over the feet during gait would influence body sway in quiet stance. Fifteen healthy males maintained the quiet stance, and we delivered moving tactile stimuli to mimic the change in their weight distribution during gait. Moving tactile stimuli did not change the length of the center of pressure (COP) displacement and COP position. Vision decreased the length of the COP, but it did not interact with moving tactile stimuli for the COP length and position. The COP position rhythmically moved in the medial-lateral axis along with the cycle of moving tactile stimuli. The COP was at the lateral peak position at the period at which moving tactile stimuli mimicked the weight distribution in the transition between the swing and stance phases of the gait cycle. This finding may indicate that the body is positioned at the lateral peak position in quiet stance when people perceive the sensation of weight distribution over the feet at the most unstable phase of the gait cycle. We suggest that moving tactile stimuli to the sole may induce medial-lateral body sway before gait initiation for patients with Parkinson's disease to improve their freezing of gait initiation.

Exercise-induced fatigue affects knee proprioceptive acuity and quadriceps neuromuscular function more in patients with ACL reconstruction or meniscus surgery than in healthy individuals

PURPOSE

To observe how knee proprioceptive acuity and quadriceps neuromuscular function change during and after repeated isokinetic knee-extension exercise in patients with anterior cruciate ligament reconstruction (ACLR) or meniscus surgery.

METHODS

Patients with ACLR or meniscus surgery and matched controls (n = 19 in each group) performed knee-flexion replication at 15° and 75°, and quadriceps peak torque (PT), central activation ratio (CAR) and rate of torque development (RTD) at baseline and immediately after every five sets of isokinetic knee-extension exercise (times 1-5).

RESULTS

Compared to the baseline, the ACLR and control groups displayed errors in knee-flexion replication at 75° only at time 5 (115.9-155.6%; p ≤ 0.04, d ≥ 0.97), whereas the meniscus surgery group exhibited errors at all time points (142.5-265.6%; p ≤ 0.0003, d ≥ 1.4). Significant percentage reductions in quadriceps CAR were observed between times 4 and 5 in the ACLR group (-5.8%; p = 0.0002, d = 0.96), but not in the meniscus surgery (-1.4%; n.s.) and control (0.1%; n.s.) groups. Significant percentage reductions in quadriceps RTD were observed between times 4 and 5 in the ACLR (-24.2%; p = 0.007, d = 0.99) and meniscus surgery (-23.0%; p = 0.01, d = 0.85) groups, but not in the control group (-0.2%; n.s.).

CONCLUSION

Patients with ACLR or meniscus surgery displayed a greater loss in knee proprioceptive acuity and quadriceps neuromuscular function during and after exercise than healthy individuals. Evidence-based interventions to enhance exercise-induced fatigue resistance should be implemented following ACLR or meniscus surgery, aiming to prevent proprioceptive and neuromuscular changes within the knee joint and quadriceps.

LEVEL OF EVIDENCE

III.

Investigating Knee Joint Proprioception and Its Impact on Limits of Stability Using Dynamic Posturography in Individuals with Bilateral Knee Osteoarthritis-A Cross-Sectional Study of Comparisons and Correlations

(1) Background: Proprioception and limits of stability can significantly impact static and dynamic balance. Knee proprioception and limits of stability may be impaired in individuals with knee osteoarthritis (KOA). Impaired knee proprioception may impact the limits of stability, and understanding the associations between these factors is important for formulating treatment strategies in this population. The objectives of this study are to (a) compare the knee joint position error (JPE) and limits of stability between KOA and asymptomatic individuals and (b) assess the correlation between knee JPE and the limits of stability in KOA individuals. (2) Methods: This cross-sectional study included 50 individuals diagnosed with bilateral KOA and 50 asymptomatic individuals. Knee JPE was measured using a dual digital inclinometer at 25° and 45° of knee flexion (in the dominant and nondominant legs). The limits of stability variables, including reaction time (s), maximum excursion (%), and direction control (%), were evaluated using computerized dynamic posturography. (3) Results: The magnitude of the mean knee JPE is significantly larger in KOA individuals (p < 0.001) compared to asymptomatic individuals assessed at 25° and 45° of knee flexion in both the dominant and nondominant legs. The limits of stability test showed that KOA group individuals had a longer reaction time (1.64 ± 0.30 s) and reduced maximum excursion (4.37 ± 0.45) and direction control (78.42 ± 5.47) percentages compared to the asymptomatic group (reaction time = 0.89 ± 0.29, maximum excursion = 5.25 ± 1.34, direction control = 87.50 ± 4.49). Knee JPE showed moderate to strong correlations with the reaction time (r = 0.60 to 0.68, p < 0.001), maximum excursion (r = -0.28 to -0.38, p < 0.001) and direction control (r = -0.59 to -0.65, p < 0.001) parameters in the limits of stability test. (4) Conclusions: Knee proprioception and limits of stability are impaired in KOA individuals compared to asymptomatic individuals, and knee JPE showed significant relationships with the limits of stability variables. These factors and correlations may be considered when evaluating and developing treatment strategies for KOA patients.

Time of Day Influence on Postural Balance of Young and Older Men

BACKGROUND

Many physiologic parameters fluctuate on a diurnal basis following the circadian rhythm function. The purpose of the study was to investigate if postural performance is interdependent of time of day and age.

METHODS

19 young (22.63 ± 3.43 y.o.) and 19 older male adults (60.21 ± 3.67 y.o.) performed three balance tests (quiet stance with open and closed eyes and bipedal balance on a Togu ball) at 12:00 AM and at 12:00 PM. Time and frequency domain variables of the center of pressure were analyzed.

RESULTS

At eyes closed test, the younger had significant less distance traveled by the Center of Pressure (CoP) at night compared to day. At open eyes test, the younger had significant less CoP sway in the anterior-posterior (AP) axis at night compared to day. At Togu ball test the older showed increased peak-to-peak amplitude of CoP in both axes compared to younger. They also had lower frequency in the medial-lateral (ML) axis but higher in the AP axis compared to the younger.

CONCLUSION

Younger seem to function better at night. There is also an indication that the older are better at day. The results on unstable surface indicate different control strategies between the two groups.

Physical Development Differences between Professional Soccer Players from Different Competitive Levels

In soccer, physical development is crucial for developing optimal performance. This study aimed to assess and compare the physical development of elite and non-elite professional soccer players. Seventy-eight male professional football players divided into four competitive levels participated in this study: the elite group (EG), the non-elite group A (NEG-A), the non-elite group B (NEG-B), and the under 23 group (U23). Body composition, static strength, lower-body explosive strength, flexibility, and balance were assessed. No significant statistical differences between elite and non-elite players were seen in body composition parameters. However, the EG performed better in static strength, lower-body explosive strength, flexibility, and balance, even after adjusting for the effects of chronological age. The analysis showed that the competitive level (group) explained 25% to 29% of the variance observed in the lower-body explosive strength tasks. Sports staff and coaches in different age categories or competitive levels should include specific lower-body explosive strength content during soccer training to promote players’ long-term development towards the elite level.

Contribution of vision and tactile sensation on body sway during quiet stance

[Purpose] This study examines the contribution of vision and tactile sensation on body sway during quiet stance. [Participants and Methods] Sixteen healthy participants maintained quiet stance. The mean distance between the neutral center of pressure (COP) and that at the peak deviated position, indicating how quickly humans initiate the swaying of the body back to the neutral position, was calculated (COPpeak). [Results] The displacement of the COP in both the anterior–posterior and medial–lateral axes was greater when vision was occluded. The anterior or posterior COPpeak was also greater when vision was occluded. The leftward COPpeak was greater when the tactile sensation of the sole was masked. Visual occlusion decreased the tactile perception threshold of the sole. There was no significant interaction between the effect of vision and that of tactile sensation on body sway during quiet stance. [Conclusion] Vision plays a role in returning the body to the neutral position, particularly in the anterior–posterior axis. Tactile sensation contributes particularly to recovery from the leftward body sway during quiet stance. Tactile sensitivity is enhanced by visual occlusion through inter-modal reweighting. However, inter-modal reweighting between vision and tactile sensation is not specifically for postural control during quiet stance.

Falls in Post-Polio Patients: Prevalence and Risk Factors

Simple Summary

People with post-polio syndrome (PPS) suffer frequent falls due to muscle weakness and problems with their balance. In order for a rehabilitation clinician to fit the patient with the optimal treatment plan to prevent imbalance and falls, we performed a simple 10-min walking test with 50 PPS patients. We also asked the patients how many falls they had experienced in the last year and they filled out a questionnaire regarding their balance confidence. We found that we can predict the occurrence of falls in PPS patients based on the consistency of their walking pattern. Since it is very easy to measure the walking pattern, our results may help rehabilitation clinicians to identify individuals at risk of fall and reduce the occurrence of falls in this population.

Abstract

Individuals with post-polio syndrome (PPS) suffer from falls and secondary damage. Aim: To (i) analyze the correlation between spatio-temporal gait data and fall measures (fear and frequency of falls) and to (ii) test whether the gait parameters are predictors of fall measures in PPS patients. Methods: Spatio-temporal gait data of 50 individuals with PPS (25 males; age 65.9 ± 8.0) were acquired during gait and while performing the Timed Up-and-Go test. Subjects filled the Activities-specific Balance Confidence Scale (ABC Scale) and reported number of falls during the past year. Results: ABC scores and number of falls correlated with the Timed Up-and-Go, and gait cadence and velocity. The number of falls also correlated with the swing duration symmetry index and the step length variability. Four gait variability parameters explained 33.2% of the variance of the report of falls (p = 0.006). The gait velocity was the best predictor of the ABC score and explained 24.8% of its variance (p = 0.001). Conclusion: Gait variability, easily measured by wearables or pressure-sensing mats, is an important predictor of falls in PPS population. Therefore, gait variability might be an efficient tool before devising a patient-specific fall prevention program for the PPS patient.

Cutaneous and muscular afferents from the foot and sensory fusion processing: Physiology and pathology in neuropathies

The foot-sole cutaneous receptors (section 2), their function in stance control (sway minimisation, exploratory role) (2.1), and the modulation of their effects by gait pattern and intended behaviour (2.2) are reviewed. Experimental manipulations (anaesthesia, temperature) (2.3 and 2.4) have shown that information from foot sole has widespread influence on balance. Foot-sole stimulation (2.5) appears to be a promising approach for rehabilitation. Proprioceptive information (3) has a pre-eminent role in balance and gait. Reflex responses to balance perturbations are produced by both leg and foot muscle stretch (3.1) and show complex interactions with skin input at both spinal and supra-spinal levels (3.2), where sensory feedback is modulated by posture, locomotion and vision. Other muscles, notably of neck and trunk, contribute to kinaesthesia and sense of orientation in space (3.3). The effects of age-related decline of afferent input are variable under different foot-contact and visual conditions (3.4). Muscle force diminishes with age and sarcopenia, affecting intrinsic foot muscles relaying relevant feedback (3.5). In neuropathy (4), reduction in cutaneous sensation accompanies the diminished density of viable receptors (4.1). Loss of foot-sole input goes along with large-fibre dysfunction in intrinsic foot muscles. Diabetic patients have an elevated risk of falling, and vision and vestibular compensation strategies may be inadequate (4.2). From Charcot-Marie-Tooth 1A disease (4.3) we have become aware of the role of spindle group II fibres and of the anatomical feet conditions in balance control. Lastly (5) we touch on the effects of nerve stimulation onto cortical and spinal excitability, which may participate in plasticity processes, and on exercise interventions to reduce the impact of neuropathy.

Association Between Back Muscle Strength and Proprioception or Mechanoreceptor Control Strategy in Postural Balance in Elderly Adults with Lumbar Spondylosis

This study aimed to investigate the relationship between back muscle strength and proprioception or mechanoreceptor control strategies used for postural balance in elderly adults with lumbar spondylosis. The displacement of the center of pressure (COP) excursion was determined in 24 elderly adults with lumbar spondylosis and 24 healthy young adults while the participants were standing upright on a balance board with their eyes closed. Vibratory stimulations of 30, 60, and 240 Hz were applied to the gastrocnemius (GS) and lumbar multifidus (LM) muscles to evaluate the effect of different proprioceptive signals on postural control. Back muscle strength was evaluated. Spearman’s rank correlation analysis was performed to determine the relationship between back muscle strength and significant COP excursion. Compared with young adults, elderly adults with lumbar spondylosis showed an increase in COP excursion displacement when a vibratory stimulation of 240 Hz was applied to the GS (P = 0.002) and LM muscles (P < 0.001). LM stimulation at 240 Hz was significantly associated with back muscle strength (P = 0.038). Postural control assessment with 240-Hz mechanoreceptor stimulation of the trunk could be a good indicator of postural instability due to over-dependence on mechanoreceptors and back muscle weakness in elderly adults with lumbar spondylosis.

Age-related changes in leg proprioception: implications for postural control

In addition to being a prerequisite for many activities of daily living, the ability to maintain steady upright standing is a relevant model to study sensorimotor integrative function. Upright standing requires managing multimodal sensory inputs to produce finely tuned motor output that can be adjusted to accommodate changes in standing conditions and environment. The sensory information used for postural control mainly arises from the vestibular system of the inner ear, vision, and proprioception. Proprioception (sense of body position and movement) encompasses signals from mechanoreceptors (proprioceptors) located in muscles, tendons, and joint capsules. There is general agreement that proprioception signals from leg muscles provide the primary source of information for postural control. This is because of their exquisite sensitivity to detect body sway during unperturbed upright standing that mainly results from variations in leg muscle length induced by rotations around the ankle joint. However, aging is associated with alterations of muscle spindles and their neural pathways, which induce a decrease in the sensitivity, acuity, and integration of the proprioceptive signal. These alterations promote changes in postural control that reduce its efficiency and thereby may have deleterious consequences for the functional independence of an individual. This narrative review provides an overview of how aging alters the proprioceptive signal from the legs and presents compelling evidence that these changes modify the neural control of upright standing.

Age-related differences in brain activity during physical and imagined sit-to-stand in healthy young and older adults

[Purpose] The purpose of this study was to investigate whether healthy young and older people differ in self-reported movement time and brain activity pattern as indicated by electroencephalography during physical and imagined sit-to-stand movements. [Participants and Methods] Twenty healthy young (aged 20–29 years) and 19 older (aged 60–69) participants performed physical and imagined sit-to-stand movements while their self-reported movement times and electroencephalography were recorded. [Results] No age-related differences were found in self-reported movement time for physical or imagined sit-to-stand. In the frontal and temporal regions, electroencephalography showed a beta wave (14–17 Hz) for all conditions in both young and older adults. In the parietal and occipital regions, during physical sit-to-stand trials, both groups showed a beta wave in both regions. During imagined sit-to-stand trials, however, young participants showed a high alpha wave (10.6–13 Hz) in the parietal and a low alpha wave (8–10.5 Hz) in the occipital region, whereas older participants showed all three (alpha and beta) waves in the parietal and occipital regions. [Conclusion] Although no age-related differences were found in the ability to generate motor imagery, brain activity pattern as indicated by electroencephalography was dissimilar between young and older participants during motor imagery.

Vestibular impairment in chronic inflammatory demyelinating polyneuropathy

Chronic inflammatory demyelinating polyneuropathy (CIDP) is a common, treatable, autoimmune peripheral neuropathy considered to produce imbalance by weakness and proprioceptive impairment rather than vestibular impairment. We measured semicircular canal vestibular function in 21 CIDP patients (15M/6F) by the video head impulse test and postural stability with a battery comprising the modified Clinical Test of Sensory Integration and Balance, the Berg Balance Scale, the Dynamic Gait Index, the Fall Efficiency Scale, and the International Cooperative Ataxia Rating Scale. Of the 21 patients, 16 had vestibular impairment, ranging from mild-affecting just a single semicircular canal, to severe-affecting all 6 canals. Although the severity of the vestibular impairment did not correlate either with the severity of the postural imbalance or of the peripheral neuropathy, our data show that vestibular impairment is an additional challenge to balance that some CIDP patients will face.

Exercise strategies to protect against the impact of short-term reduced physical activity on muscle function and markers of health in older men: study protocol for a randomised controlled trial

Background

Muscles get smaller and weaker as we age and become more vulnerable to atrophy when physical activity is reduced or removed. This research is designed to investigate the potentially protective effects of two separate exercise strategies against loss in skeletal muscle function and size, and other key indices of health, following 14 days of reduced physical activity in older men.

Methods

Three groups of 10 older men (aged 65–80 years) will undertake 2 weeks of reduced activity by decreasing daily steps from more than 3500 to less than 1500 (using pedometers to record step count). Two of the three groups will then undertake additional exercise interventions, either: 4 weeks of progressive resistance training prior to the step-reduction intervention (PT-group), or home-based ‘exercise snacking’ three times per day during the step-reduction intervention (ES-group). The third group undertaking only the step-reduction intervention (control) will provide a comparison against which to assess the effectiveness of the protective exercise strategies. Pre and post step-reduction assessments of muscle function, standing balance, anthropometry and muscle architecture will be taken. Pre and post step-reduction in postprandial metabolic control, resting systemic inflammation, adipose inflammation, oxidative stress, immune function, sleep quality, dietary habits, and quality of life will be measured. The stress response to exercise, and signalling protein and gene expression for muscle protein synthesis and breakdown following an acute bout of exercise will also be assessed pre and post step-reduction. Rates of muscle protein synthesis and adipose triglyceride turnover during the step-reduction intervention will be measured using stable isotope methodology. All participants will then undertake 2 weeks of supervised resistance training with the aim of regaining any deficit from baseline in muscle function and size.

Discussion

This study aims to identify exercise strategies that could be implemented to protect against loss of muscle power during 2 weeks of reduced activity in older men, and to improve understanding of the way in which a short-term reduction in physical activity impacts upon muscle function and health.

Trial registration

ClinicalTrials.gov: NCT02495727 (Initial registration: 25 June 2015)

Stance Postural Strategies in Patients with Chronic Inflammatory Demyelinating Polyradiculoneuropathy

Introduction

Polyneuropathy leads to postural instability and an increased risk of falling. We investigated how impaired motor impairment and proprioceptive input due to neuropathy influences postural strategies.

Methods

Platformless bisegmental posturography data were recorded in healthy subjects and patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Each subject stood on the floor, wore a head and a hip electromagnetic tracker. Sway amplitude and velocity were recorded and the mean direction difference (MDD) in the velocity vector between trackers was calculated as a flexibility index.

Results

Head and hip postural sway increased more in patients with CIDP than in healthy controls. MDD values reflecting hip strategies also increased more in patients than in controls. In the eyes closed condition MDD values in healthy subjects decreased but in patients remained unchanged.

Discussion

Sensori-motor impairment changes the balance between postural strategies that patients adopt to maintain upright quiet stance. Motor impairment leads to hip postural strategy overweight (eyes open), and prevents strategy re-balancing when the sensory context predominantly relies on proprioceptive input (eyes closed).

Proprioceptive acuity predicts muscle co-contraction of the tibialis anterior and gastrocnemius medialis in older adults' dynamic postural control

Older adults use a different muscle strategy to cope with postural instability, in which they 'co-contract' the muscles around the ankle joint. It has been suggested that this is a compensatory response to age-related proprioceptive decline however this view has never been assessed directly. The current study investigated the association between proprioceptive acuity and muscle co-contraction in older adults. We compared muscle activity, by recording surface electromyography (EMG) from the bilateral tibialis anterior (TA) and gastrocnemius medialis (GM) muscles, in young (aged 18-34) and older adults (aged 65-82) during postural assessment on a fixed and sway-referenced surface at age-equivalent levels of sway. We performed correlations between muscle activity and proprioceptive acuity, which was assessed using an active contralateral matching task. Despite successfully inducing similar levels of sway in the two age groups, older adults still showed higher muscle co-contraction. A stepwise regression analysis showed that proprioceptive acuity measured using variable error was the best predictor of muscle co-contraction in older adults. However, despite suggestions from previous research, proprioceptive error and muscle co-contraction were negatively correlated in older adults, suggesting that better proprioceptive acuity predicts more co-contraction. Overall, these results suggest that although muscle co-contraction may be an age-specific strategy used by older adults, it is not to compensate for age-related proprioceptive deficits.

Pisa Syndrome in Parkinson's Disease: Electromyographic Aspects and Implications for Rehabilitation

Pisa Syndrome (PS) is a real clinical enigma, and its management remains a challenge. In order to improve the knowledge about resting state and during maximal voluntary muscle contraction (MVMC) of the axial muscles, we described the electromyography results of paraspinal muscles, rectus abdominis, external oblique, and quadratus lumborum of both sides of 60 patients. Electromyography was assessed at rest, during MVMC while bending in the opposite direction of the PS and during MVMC while bending in the direction of the PS. The MVMC gave information about the interferential pattern (INT) or subinterferential pattern (sub-INT). We defined asymmetrical activation (AA) when a sub-INT was detected on the muscle on the side opposite to the PS bending and an INT of same muscle in the direction of PS bending. We observed significant AA during MVMC only in the external oblique muscles in 78% of the subjects. Our results of asymmetric ability to generate maximal voluntary force of the external oblique muscles support a central dissynchronisation of axial muscles as a significant contributor for the bending of the spine in erect position. These results could have important implication to physiotherapy and the use of botulinum toxin in the treatment of PS.

The impact of previous knee injury on force plate and field-based measures of balance

BACKGROUND

Individuals with post-traumatic osteoarthritis demonstrate increased sway during quiet stance. The prospective association between balance and disease onset is unknown. Improved understanding of balance in the period between joint injury and disease onset could inform secondary prevention strategies to prevent or delay the disease. This study examines the association between youth sport-related knee injury and balance, 3-10years post-injury.

METHODS

Participants included 50 individuals (ages 15-26years) with a sport-related intra-articular knee injury sustained 3-10years previously and 50 uninjured age-, sex- and sport-matched controls. Force-plate measures during single-limb stance (center-of-pressure 95% ellipse-area, path length, excursion, entropic half-life) and field-based balance scores (triple single-leg hop, star-excursion, unipedal dynamic balance) were collected. Descriptive statistics (mean within-pair difference; 95% confidence intervals) were used to compare groups. Linear regression (adjusted for injury history) was used to assess the relationship between ellipse-area and field-based scores.

FINDINGS

Injured participants on average demonstrated greater medio-lateral excursion [mean within-pair difference (95% confidence interval); 2.8mm (1.0, 4.5)], more regular medio-lateral position [10ms (2, 18)], and shorter triple single-leg hop distances [-30.9% (-8.1, -53.7)] than controls, while no between group differences existed for the remaining outcomes. After taking into consideration injury history, triple single leg hop scores demonstrated a linear association with ellipse area (β=0.52, 95% confidence interval 0.01, 1.01).

INTERPRETATION

On average the injured participants adjusted their position less frequently and demonstrated a larger magnitude of movement during single-limb stance compared to controls. These findings support the evaluation of balance outcomes in the period between knee injury and post-traumatic osteoarthritis onset.

Effects of the site and extent of plantar cutaneous stimulation on dynamic balance and muscle activity while walking

BACKGROUND

Previous studies have demonstrated that stimulating the cutaneous plantar sensory receptors of the foot through textured insoles improves human balance and walking. This study investigated the effect of medial and lateral zoned textured insoles using tibialis anterior/peroneus longus surface electromyographic activity and Centre-of-Pressure as indicators of postural stability while walking.

METHODS

15 asymptomatic subjects were tested using a within-subject randomised repeated measures design. The effect of lateral and medial zoned insoles of varying heights (control, 2, 4 and 6mm) on stability while walking under normal and impaired visual conditions was assessed.

RESULTS

Impaired vision resulted in an increase in foot CoP variability while walking (p<0.05). The laterally zoned insole was associated with a significant (repeated measures ANOVA p<0.05) increase in the rate of medial-lateral CoP change.

CONCLUSION

These findings suggest that the site of stimulation of the plantar foot cutaneous receptors may increase postural instability during walking. This should be considered in the design of insoles that aim to improve balance and reduce falls risk. The importance of vision in balance control has been highlighted and using impaired vision may serve as a way of trialling clinical products in the healthy population.

Association of Postural Sway with Disability Status and Cerebellar Dysfunction in People with Multiple Sclerosis: A Preliminary Study

BACKGROUND

The aims of this study were 1) to examine postural sway in the eyes open (EO) and eyes closed (EC) conditions in people with multiple sclerosis (MS) with moderate levels of disability compared with controls and 2) to examine relationships between postural sway and total Expanded Disability Status Scale (EDSS) scores, functional system subscores, and clinical measures of strength and spasticity in the MS group.

METHODS

Thirty-four people with moderate MS and ten matched controls completed measures of postural sway with EO and EC, knee extension and ankle dorsiflexion isometric strength, EDSS total score and subscores, and spasticity levels.

RESULTS

Participants with MS swayed significantly more with EO and EC and had reduced knee extension and ankle dorsiflexion strength compared with controls (P < .001). In the MS group, increased sway was associated with higher total EDSS scores and cerebellar function subscores, whereas increased sway ratio (EC/EO) was associated with reduced sensory function subscores. Postural sway was not significantly associated with strength or spasticity.

CONCLUSIONS

Participants with MS swayed more and were significantly weaker than controls. Cerebellar dysfunction was identified as the EDSS domain most strongly associated with increased sway, and sensory loss was associated with a relatively greater dependence on vision for balance control. These findings suggest that exercise interventions targeting sensory integration and cerebellar ataxia may be beneficial for enhancing balance control in people with MS.

Discordance in recovery between altered locomotion and muscle atrophy induced by simulated microgravity in rats

Exposure to a microgravity environment leads to adverse effects in motion and musculoskeletal properties. However, few studies have investigated the recovery of altered locomotion and muscle atrophy simultaneously. The authors investigated altered locomotion in rats submitted to simulated microgravity by hindlimb unloading for 2 weeks. Motion deficits were characterized by hyperextension of the knees and ankle joints and forward-shifted limb motion. Furthermore, these locomotor deficits did not revert to their original form after a 2-week recovery period, although muscle atrophy in the hindlimbs had recovered, implying discordance in recovery between altered locomotion and muscle atrophy, and that other factors such as neural drives might control behavioral adaptations to microgravity.

Effects of whole body vibration training on people with chronic stroke: a systematic review and meta-analysis

BACKGROUND

The effects of whole body vibration (WBV) on chronic stroke (CS) patients have been investigated by some previous studies. However, controversy still exists.

OBJECTIVE

The objective of this meta-analysis was to review existing studies that assess the effects of WBV training on CS patients.

METHODS

We searched Medline, Web of Science, EMBASE, and the Cochrane Library for papers published between January 2000 and January 2014.The meta-analyses were performed using Review Manage Version 5.2.Weighted mean difference (WMD) or standard mean difference (SMD) and its 95% confidence intervals (CI) were used as summary statistics. Funnel plot was used to assess the publication bias.

RESULTS

Seven studies with 298 CS patients (159 patients underwent WBV training in experimental group and 139 patients underwent nothing or the same exercise without vibration or with a "placebo" vibrating platform in control group) were included. No significant difference was found in muscle strength (isometric knee extension strength: SMD = - 0.15, 95% CI, - 0.43 to 0.13, P = 0.30; isometric knee flexion strength: WMD = - 0.05, 95% CI, - 0.13 to 0.03, P = 0.22), balance (berg balance scale, WMD = - 0.23, 95% CI, - 1.54 to 1.09; P = 0.74) and gait performance (6-min walk test, WMD = - 50.40, 95% CI, - 118.14 to 17.34; P = 0.14) between groups. No indication of publication bias was found in the funnel plot.

CONCLUSIONS

WBV training had no beneficial effects in muscle strength, balance and gait performance of CS patients.

Dorsiflexion assist orthosis reduces the physiological cost and mitigates deterioration in strength and balance associated with walking in people with multiple sclerosis

OBJECTIVE

To evaluate the effect of wearing a dorsiflexion assist orthosis (DAO) on walking distance, physiological cost, fatigue, and strength and balance measures after a modified 6-minute walk test (6MWT) in people with multiple sclerosis (MS).

DESIGN

Randomized crossover trial.

SETTING

Hospital Movement Laboratory.

PARTICIPANTS

People with moderate MS and Expanded Disability Status Scale score of 3.7±0.7 (N=34; 26 women).

INTERVENTIONS

Modified 6MWT with and without a DAO worn on the weaker leg.

MAIN OUTCOME MEASURES

Distance walked, perceived fatigue, and the physiological cost of walking were compared between walking conditions. Pre- and postwalk changes in knee extensor and ankle dorsiflexor isometric strength and standing postural sway with eyes open and closed were compared between walking conditions.

RESULTS

There were no differences in distance walked or perceived fatigue between the 2 walking conditions. However, there was a reduced physiological cost of walking (P<.05), a smaller reduction in knee extensor strength (P<.05), and a smaller increase in standing postural sway with eyes open (P<.01) after walking while wearing the DAO compared with walking without wearing the DAO.

CONCLUSIONS

Despite not increasing walking distance or reducing perceived fatigue, the DAO reduced the physiological cost of walking and maintained knee strength and standing balance, which may have important implications for physical rehabilitation in people with MS. Further trials are required to determine whether the beneficial effects of wearing a DAO found here are maintained for longer periods.

Two-year exercise program improves physical function in Parkinson's disease: the PRET-PD randomized clinical trial

Background. The progressive resistance exercise (PRE) in Parkinson's disease trial (PRET-PD) showed that PRE improved the motor signs of PD compared to a modified Fitness Counts (mFC) program. It is unclear how long-term exercise affects physical function in these individuals. Objective. To examine the effects of long-term PRE and mFC on physical function outcome measures in individuals with PD. Methods. A preplanned secondary analysis was conducted using data from the 38 patients with idiopathic PD who completed the PRET-PD trial. Participants were randomized into PRE or mFC groups and exercised 2 days/week up to 24 months. Blinded assessors obtained functional outcomes on and off medication at baseline, 6 and 24 months with the Modified Physical Performance Test, 5 times sit to stand test, Functional Reach Test, Timed Up and Go, Berg Balance Scale, 6 minute walk test (6MWT), and 50-ft walking speed (walk speed). Results. The groups did not differ on any physical function measure at 6 or 24 months (Ps > .1). Across time, all physical function measures improved from baseline to 24 months when tested on medication (Ps < .0001), except for 6MWT (P = .068). Off medication results were similar except that the 6MWT was now significant. Conclusions. Twenty-four months of supervised and structured exercise (either PRE or mFC) is effective at improving functional performance outcomes in individuals with moderate PD. Clinicians should strive to include structured and supervised exercise in the long-term plan of care for individuals with PD.

Fatigue-induced balance impairment in young soccer players

CONTEXT

Although balance is generally recognized to be an important feature in ensuring good performance in soccer, its link with functional performance remains mostly unexplored, especially in young athletes.

OBJECTIVE

To investigate changes in balance induced by fatigue for unipedal and bipedal static stances in young soccer players.

DESIGN

Crossover study.

SETTING

Biomechanics laboratory and outdoor soccer field.

PATIENTS OR OTHER PARTICIPANTS

Twenty-one male soccer players (age = 14.5 ± 0.2 years, height = 164.5 ± 5.6 cm, mass = 56.8 ± 6.8 kg).

INTERVENTION(S)

Static balance was assessed with postural-sway analysis in unipedal and bipedal upright stance before and after a fatigue protocol consisting of a repeated sprint ability (RSA) test (2 × 15-m shuttle sprint interspersed with 20 seconds of passive recovery, repeated 6 times).

MAIN OUTCOME MEASURE(S)

On the basis of the center-of-pressure (COP) time series acquired during the experimental tests, we measured sway area, COP path length, and COP maximum displacement and velocity in the anteroposterior and mediolateral directions.

RESULTS

Fatigue increased all sway values in bipedal stance and all values except COP velocity in the mediolateral direction in unipedal stance. Fatigue index (calculated on the basis of RSA performance) was positively correlated with fatigue/rest sway ratio for COP path length and COP velocity in the anteroposterior and mediolateral directions for nondominant single-legged stance.

CONCLUSIONS

Fatigued players exhibited reduced performance of the postural-control system. Participants with better performance in the RSA test appeared less affected by balance impairment, especially in single-legged stance.

Posture and cognition in the elderly: interaction and contribution to the rehabilitation strategies

In this paper we review the effects of aging on sensory systems and their impact on posture, balance and gait. We also address cognitive aging and attempt to specify which altered cognitive functions negatively impact balance and walking. The role of cognition in postural control is tested with dual-task experiments. This situation results in deleterious effects due to an attentional overload. Given the human cognitive system has limited capacities, we propose that simultaneously performing two tasks depends on the capacity of each individual to perform these tasks on a continuum between automatic execution to highly controlled performance. A level of maximum control exceeds the subject's attentional capacity, which makes it impossible to perform both tasks simultaneously. The subject therefore prioritizes one of the tasks. We use representative dual-task studies from the literature to illustrate the relationship between the different cognitive components and their impact on the control of posture and gait in elderly subjects with altered cognitive capacities and with elderly subjects who are fallers or who have altered sensory-motor capacities. Recently this postural-cognitive relationship was addressed with a new approach. We report how cognitive training can improve dual-task management and we attempt to define the cognitive mechanisms that may be responsible for better postural balance.

Effect of 14 days of bed rest in older adults on parameters of the body sway and on the local ankle function

This study explored the effects of a 14-day horizontal bed rest (BR) without countermeasures on postural sway, maximal voluntary torque and precision of voluntary torque matching. Sixteen subjects were tested before, immediately after and two weeks after BR. The increase in frequency and amplitude after BR was comparable for both sway subcomponents (rambling and trembling) in medial-lateral direction. But in anterior-posterior direction, rambling increased more in frequency (-7% vs. +31%, p < 0.05) while trembling increased more in amplitude (+35% vs. +84%, p < 0.05). The drop in maximal voluntary torque after BR was present for plantar flexion (p < 0.05) but not for dorsal flexion. After the BR, the subjects were less precise in the dorsal flexion torque matching task (p < 0.05). All the observed parameters, except the dorsal flexion torque matching error, returned back to the pre-BR values after the two weeks of re-conditioning. Results of this study indicate that body sway subcomponents responded differently to BR. Based on these findings, it was not possible to draw clear assumptions on the effects of neural and structural changes on body sway.

The effect of vision elimination during quiet stance tasks with different feet positions

Literature confirms the effects of vision and stance on body sway and indicates possible interactions between the two. However, no attempts have been made to systematically compare the effect of vision on the different types of stance which are frequently used in clinical and research practice. The biomechanical changes that occur after changing shape and size of the support surface suggest possible sensory re-weighting might take place. The purpose of this study was to assess the effect of vision on body sway in relation to different stance configurations and width. Thirty-eight volunteers performed four quiet stance configurations (parallel, semi-tandem, tandem and single leg), repeating them with open and closed eyes. Traditional parameters, recurrence quantification analysis and sample entropy were analyzed from the CoP trajectory signal. Traditional and recurrence quantification analysis parameters were affected by vision removal and stance type. Exceptions were frequency of oscillation, entropy and trapping time. The most prominent effect of vision elimination on traditional parameters was observed for narrower stances. A significant interaction effect between vision removal and stance type was present for most of the parameters observed (p<0.05). The interaction effect between medio-lateral and antero-posterior traditional parameters differed in linearity between stances. The results confirm the effect of vision removal on the body sway. However, for the medio-lateral traditional parameters, the effects did not increase linearly with the change in width and stance type. This suggests that removal of vision could be more effectively compensated by other sensory systems in semi-tandem stance, tandem and single legged stance.

Knee joint stabilization therapy in patients with osteoarthritis of the knee: a randomized, controlled trial

OBJECTIVE

To investigate whether an exercise program, initially focusing on knee stabilization and subsequently on muscle strength and performance of daily activities is more effective than an exercise program focusing on muscle strength and performance of daily activities only, in reducing activity limitations in patients with knee osteoarthritis (OA) and instability of the knee joint.

DESIGN

A single-blind, randomized, controlled trial involving 159 knee OA patients with self-reported and/or biomechanically assessed knee instability, randomly assigned to two treatment groups. Both groups received a supervised exercise program for 12 weeks, consisting of muscle strengthening exercises and training of daily activities, but only in the experimental group specific knee joint stabilization training was provided. Outcome measures included activity limitations (Western Ontario and McMaster Universities Osteoarthritis Index - WOMAC physical function, primary outcome), pain, global perceived effect and knee stability.

RESULTS

Both treatment groups demonstrated large (∼20-40%) and clinically relevant reductions in activity limitations, pain and knee instability, which were sustained 6 months post-treatment. No differences in effectiveness between experimental and control treatment were found on WOMAC physical function (B (95% confidence interval - CI) = -0.01 (-2.58 to 2.57)) or secondary outcome measures, except for a higher global perceived effect in the experimental group (P = 0.04).

CONCLUSIONS

Both exercise programs were highly effective in reducing activity limitations and pain and restoring knee stability in knee OA patients with instability of the knee. In knee OA patients suffering from knee instability, specific knee joint stabilization training, in addition to muscle strengthening and functional exercises, does not seem to have any additional value. Dutch Trial Register (NTR) registration number: NTR1475.

The proprioceptive senses: their roles in signaling body shape, body position and movement, and muscle force

This is a review of the proprioceptive senses generated as a result of our own actions. They include the senses of position and movement of our limbs and trunk, the sense of effort, the sense of force, and the sense of heaviness. Receptors involved in proprioception are located in skin, muscles, and joints. Information about limb position and movement is not generated by individual receptors, but by populations of afferents. Afferent signals generated during a movement are processed to code for endpoint position of a limb. The afferent input is referred to a central body map to determine the location of the limbs in space. Experimental phantom limbs, produced by blocking peripheral nerves, have shown that motor areas in the brain are able to generate conscious sensations of limb displacement and movement in the absence of any sensory input. In the normal limb tendon organs and possibly also muscle spindles contribute to the senses of force and heaviness. Exercise can disturb proprioception, and this has implications for musculoskeletal injuries. Proprioceptive senses, particularly of limb position and movement, deteriorate with age and are associated with an increased risk of falls in the elderly. The more recent information available on proprioception has given a better understanding of the mechanisms underlying these senses as well as providing new insight into a range of clinical conditions.

Interpreting the need for initial support to perform tandem stance tests of balance

BACKGROUND

Geriatric rehabilitation reimbursement increasingly requires documented deficits on standardized measures. Tandem stance performance can characterize balance, but protocols are not standardized. Objective The purpose of this study was to explore the impact of: (1) initial support to stabilize in position and (2) maximum hold time on tandem stance tests of balance in older adults. Design A cross-sectional secondary analysis of observational cohort data was conducted.

METHODS

One hundred seventeen community-dwelling older adults (71% female, 12% black) were assigned to 1 of 3 groups based on the need for initial support to perform tandem stance: (1) unable even with support, (2) able only with support, and (3) able without support. The able without support group was further stratified on hold time in seconds: (1) <10 (low), (2) 10 to 29, (medium), and (3) 30 (high). Groups were compared on primary outcomes (gait speed, Timed "Up & Go" Test performance, and balance confidence) using analysis of variance.

RESULTS

Twelve participants were unable to perform tandem stance, 14 performed tandem stance only with support, and 91 performed tandem stance without support. Compared with the able without support group, the able with support group had statistically or clinically worse performance and balance confidence. No significant differences were found between the able with support group and the unable even with support group on these same measures. Extending the hold time to 30 seconds in a protocol without initial support eliminated ceiling effects for 16% of the study sample. Limitations Small comparison groups, use of a secondary analysis, and lack of generalizability of results were limitations of the study.

CONCLUSIONS

Requiring initial support to stabilize in tandem stance appears to reflect meaningful deficits in balance-related mobility measures, so failing to consider support may inflate balance estimates and confound hold time comparisons. Additionally, 10-second maximum hold times limit discrimination of balance in adults with a higher level of function. For community-dwelling older adults, we recommend timing for at least 30 seconds and documenting initial support for consideration when interpreting performance.

Effects of vertical center of mass redistribution on body sway parameters during quiet standing

Body sway is usually described by center of foot pressure (COP)-derived parameters. Their sensitivity to vertical center of mass (COM) redistribution below its natural position has not yet been examined during quiet stance tasks. We examined the effects of both lowering and raising the COM on the following body sway parameters: cumulative, medial-lateral and anterior-posterior COP average velocity, amplitude and frequency. For this purpose, 13 healthy male subjects performed a quiet stance balance task with feet positioned in parallel stance (PS) at hip width apart and with hands holding a stick across the rear part of the shoulders. Each subject carried out five different modifications of the PS task in a randomized order: no additional load, an additional load of 10 kg and 30 kg suspended from the waist at mid-lower leg height, and an additional load of 10 kg and 30 kg across the rear of the shoulders. The studied body sway parameters proved to be sensitive to these manipulations. Specifically, lowering and raising the COM was mirrored in a systematic decrease/increase of the velocity, amplitude, and frequency parameters, indicating a larger effect in the anterior-posterior direction. These results suggest that the elevation of the body COM from a lower to a higher position systematically decreases the postural control during quiet standing, and consequently, increases the intensity of the balancing task. Thus, this type of physical manipulation could provide the basis for a simple progression in functional resistance training for persons with compromised balance.

The effect of fatigue from exercise on human limb position sense

We have previously shown, in a two-limb position-matching task in human subjects, that exercise of elbow flexors of one arm led the forearm to be perceived as more extended, while exercise of knee extensors of one leg led the lower leg to be perceived as more flexed. These findings led us to propose that exercise disturbs position sense because subjects perceive their exercised muscles as longer than they actually are. In order to obtain further support for this hypothesis, in the first experiment reported here, elbow extensors were exercised, with the prediction that the exercised arm would be perceived as more flexed after exercise. The experiment was carried out under three load conditions, with the exercised arm resting on a support, with it supporting its own weight and with it supporting a load of 10% of its voluntary contraction strength. For each condition, the forearm was perceived as more extended, not more flexed, after exercise. This result was confirmed in a second experiment on elbow flexors. Again, under all three conditions the exercised arm was perceived as more extended. To explore the distribution of the phenomenon, in a third experiment finger flexor muscles were exercised. This had no significant effect on position sense at the elbow. In a fourth experiment, position sense at the knee was measured after knee flexors of one leg were exercised and, as for knee extensors, it led subjects to perceive their exercised leg to be more flexed at the knee than it actually was. Putting all the observations together, it is concluded that while the influences responsible for the effects of exercise may have a peripheral origin, their effect on position sense occurs centrally, perhaps at the level of the sensorimotor cortex.

Stabilometry is a predictor of gait performance in chronic hemiparetic stroke patients

In patients with spastic hemiparesis, centre of foot pressure (CoP) is shifted toward the unaffected limb during quiet stance. We hypothesised that abnormal gait features would correlate with the degree of asymmetry during stance. In 15 patients and 17 normals we recorded CoP and body sway by a force platform and measured spatial-temporal variables of gait with pedobarography. In patients CoP was shifted toward the unaffected limb and sway was larger than in normals. CoP position was associated with the decrease in strength of the affected lower-limb muscles. Spatio-temporal variables of gait were also affected by the disease. Cadence and velocity were decreased, duration of single support on the unaffected limb and of double support were increased with respect to normals. The degree of impairment of gait variables correlated with CoP. We found a negative relationship between velocity or cadence and CoP, and a positive relationship between duration of single support and CoP in the unaffected but not in the affected limb. Duration of double support correlated positively with CoP. CoP asymmetry during both standing and walking suggests that postural and gait problems share some common neural origin in hemiparetic patients. This asymmetry affects gait performance by increasing the time and effort needed to shift body weight toward the affected limb. The degree of postural asymmetry measured by stabilometry is associated with the level of impairment of gait variables.