Altered muscle activation characteristics associated with single volitional forward stepping in middle-aged adults

Background

Middle-aged adults show a higher incidence of falls compared to young adults when performing outdoor physical activities. This study investigated whether or not the patterns and quantitative characteristics of the trunk and lower extremity muscle activations associated with stepping, which represents an important movement for arresting falls, differ between middle-aged adults and young adults.

Methods

Nine healthy young adults (age = 22[3] years) and nine healthy middle-aged adults (age = 52[8] years), performed a single-step, volitional, fast forward stepping movement with each leg. The stepping movement was divided into the step-initiation, single-leg-support, and landing phases based on foot-switch signals. The activation sequence, occurrence rate, onset latency, burst duration, and normalized co-contraction duration of the tibialis anterior, medial gastrocnemius, rectus femoris, biceps femoris, and gluteus medius of the stance and swing legs and that of bilateral erector spinae muscles were analyzed using surface electromyography. We defined the essential muscle activation as exhibiting an occurrence rate of 90% or more in all of these trials.

Findings

As compared to young adults, the middle-aged adults demonstrated several additional essential bursts throughout the stepping movement. Middle-aged adults also displayed significantly longer burst durations of the biceps femoris and medial gastrocnemius of the swing leg after landing, as well as longer co-contraction of the rectus femoris and biceps femoris of the stance leg in the single-leg-support phase (P < 0.05).

Interpretation

Age-related changes in step-related neuromuscular control exist in healthy middle-aged adults. We propose that training focused on improving or maintaining neuromuscular control associated with volitional leg movements may benefit middle-aged individuals.     

Voluntary sway and rapid orthogonal transitions of voluntary sway in young adults,and low and high fall-risk older adults

Background

Falls amongst older people have been linked to reduced postural stability and slowed movement responses. The objective of this study was to examine differences in postural stability and the speed of response between young adults, low fall-risk older adults, and high fall-risk older adults during voluntary postural sway movements.

Methods

Twenty-five young adults (25 ± 4 years), and 32 low fall-risk (74 ± 5 years), and 16 high fall-risk (79 ± 7 years) older adults performed voluntary sway and rapid orthogonal transitions of voluntary sway between the anterior–posterior and medial–lateral directions. Measures included reaction and movement time and the amplitudes of the centre of pressure, centre of mass, and the separation distance between the centre of pressure and centre of mass.

Findings

Both fall-risk groups compared to the young had slower reaction and movement time, greater centre of pressure and/or centre of mass amplitude in the orthogonal (non-target) direction during voluntary sway, and reduced anterior–posterior and medial–lateral separation between the centre of pressure and centre of mass during voluntary sway and orthogonal transitions. High compared to low fall-risk individuals had slower reaction and movement time, increased non-target centre of mass amplitude during voluntary sway, and reduced medial–lateral centre of pressure and centre of mass separation during voluntary sway and orthogonal transitions.

Interpretation

Age-related deterioration of postural control resulted in slower reactive responses and reduced control of the direction of body movement during voluntary sway and orthogonal transitions. Slower postural reaction and movement time and reduced medial–lateral control of the centre of mass during voluntary sway movements are associated with increased fall-risk in community-living older people.     

Postural Response Latencies Are Related to Balance Control During Standing and Walking in Patients With Multiple Sclerosis

Objective

To understand and examine the relation between postural response latencies obtained during postural perturbations and representative measures of balance during standing (sway variables) and walking (trunk motion).

Design

Cross-sectional.

Setting

University medical center.

Participants

Persons with multiple sclerosis (MS) (n=40) were compared with similar aged control subjects (n=20). There were 20 subjects with MS in the normal walking velocity group and 20 subjects with MS who had slow walking velocity based on a timed 25-foot walk (T25FW) of <5 seconds.

Interventions

None.

Main Outcome Measures

Postural response latency, sway variables, trunk motion variables.

Results

We found that subjects with MS with both slow or normal walking velocities had significantly longer postural response latencies than the healthy control group. Postural response latency was not correlated with the T25FW. Postural response latency was significantly correlated with center of pressure sway variables during quiet standing (root mean square: ρ=.334, P=.04; range: ρ=.385, P=.017; mean velocity: ρ=.337, P=.038; total sway area: ρ=.393, P=.015). Postural response latency was also significantly correlated with motion of the trunk during walking (sagittal plane range of motion: ρ=.316, P=.05; SD of transverse plane range of motion: ρ=−.43, P=.006).

Conclusions

These findings clearly indicate that slow postural responses to external perturbations in patients with MS contribute to disturbances in balance control during both standing and walking.     

Nonlinear analysis of sitting postural sway indicates developmental delay in infants

Background

Upright sitting is one of the first developmental motor milestones achieved by infants, and sitting postural sway provides a window into the developing motor control system. A variety of posture sway measures can be used, but the optimal measures for infant development have not been identified.

Methods

We have collected sitting postural sway data from two groups of infants, one with typical development (n = 33), and one with delayed development and either diagnosed with or at risk for cerebral palsy (n = 26), when the infants had developed to the point where they could just maintain sitting for about 10 s. Postural sway data was collected while infants were sitting on a force platform, and the center of pressure was analyzed using both linear and nonlinear measures.

Findings

Our results showed that a nonlinear measure, the largest Lyapunov exponent, was the only parameter of postural sway that revealed significant differences between infants with typical versus delayed development. The largest Lyapunov exponent was found to be higher for typically developing infants, indicating less repeated patterning in their movement coordination.

Interpretations

A nonlinear measure such as largest Lyapunov exponent may be useful as an identifier of pathology and as a yardstick for the success of therapeutic interventions.     

Postural balance under normal and altered sensory conditions in normal-weight and overweight children

Background

Little or no research has been done in the overweight child on the relative contribution of multisensory information to maintain postural stability. Therefore, the purpose of this study was to investigate postural balance control under normal and experimentally altered sensory conditions in normal-weight versus overweight children.

Methods

Sixty children were stratified into a younger (7–9 yr) and an older age group (10–12 yr). Participants were also classified as normal-weight (n = 22) or overweight (n = 38), according to the international BMI cut-off points for children. Postural stability was assessed during quiet bilateral stance in four sensory conditions (eyes open or closed, normal or reduced plantar sensation), using a Kistler force plate to quantify COP dynamics. Coefficients of variation were calculated as well to describe intra-individual variability.

Findings

Removal of vision resulted in systematically higher amounts of postural sway, but no significant BMI group differences were demonstrated across sensory conditions. However, under normal conditions lower plantar cutaneous sensation was associated with higher COP velocities and maximal excursion of the COP in the medial-lateral direction for the overweight group. Regardless of condition, higher variability was shown in the overweight children within the 7–9 yr old subgroup for postural sway velocity, and more specifically medial–lateral velocity.

Interpretation

In spite of these subtle differences, results did not establish any clear underlying sensory organization impairments that may affect standing balance performance in overweight children compared to normal-weight peers. Consequently, it is believed that other factors account for overweight children's functional balance deficiencies.     

Evaluation of static and dynamic postural stability in established rheumatoid arthritis: Exploratory study

Background

It has been proposed that people with rheumatoid arthritis experience difficulties in postural control and activities of daily living such as walking. The aim of the study is to evaluate postural stability in rheumatoid arthritis patients.

Method

A convenience sample of 19 rheumatoid arthritis patients (mean duration 13.1 ± 9.2 years) were aged matched with a non-rheumatoid group (n = 21). Postural stability was measured using a force plate for anterior–posterior and mediolateral centre of pressure excursion for 30 s with eyes closed and open. Patients also performed three walks at a self-selected speed and mean temporal–spatial parameters were recorded.

Findings

Significant differences were observed between the groups in anterior–posterior centre of pressure excursion during the eyes open task and the eyes closed task (P < 0.05). No significant differences were found in the mediolateral centre of pressure excursion during either condition (P > 0.05). The rheumatoid group displayed a significantly slower mean walking velocity, double support, cadence and cycle time than the non-rheumatoid group (P < 0.05).

Interpretation

The results from this study showed that rheumatoid arthritis patients displayed a significantly larger centre of pressure excursion in the anterior–posterior direction during quiet standing, when compared to a non-rheumatoid arthritis control group suggesting that postural control mechanisms such as ankle strategies are impeded by the rheumatoid process.     

Postural stability and ankle sprain history in athletes compared to uninjured controls

Background

Diminished postural stability is a risk factor for ankle sprain occurrence and ankle sprains result in impaired postural stability. To date, ankle sprain history has not been taken into account as a determinant of postural stability, while it could possibly specify subgroups of interest.

Methods

Postural stability was compared between 18 field hockey athletes who had recovered from an ankle sprain (mean (SD); 3.6 (1.5) months post-injury), and 16 uninjured controls. Force plate and kinematics parameters were calculated during single-leg standing: mean center of pressure speed, mean absolute horizontal ground reaction force, mean absolute ankle angular velocity, and mean absolute hip angular velocity. Additionally, cluster analysis was applied to the ‘injured’ participants, and the cluster with diminished postural stability was compared to the other participants with respect to ankle sprain history.

Findings

MANCOVA showed no significant difference between groups in postural stability (P = 0.68). A self-reported history of an (partial) ankle ligament rupture was typically present in the cluster with diminished postural stability. Subsequently, a ‘preceding rupture’ was added as a factor in the MANCOVA, which showed a significant association between diminished postural stability and a ‘preceding rupture’ (P = 0.01), for all four individual parameters (P: 0.001–0.029; Cohen's d: 0.96–2.23).

Interpretation

Diminished postural stability is not apparent in all previously injured athletes. However, our analysis suggests that an (mild) ankle sprain with a preceding severe ankle sprain is associated with impaired balance ability. Therefore, sensorimotor training may be emphasized in this particular group and caution is warranted in return to play decisions.     

The effects of sandals on postural stability in patients with rheumatoid arthritis: An exploratory study

Background

Rheumatoid arthritis results in postural instability, pain and functional limitations. As rheumatoid arthritis progresses, localised forefoot deformities such as hallux valgus and clawing of the lesser toes occur, leading to a high proportion of people with rheumatoid arthritis wearing sandals. Sandals may affect postural stability due to poor motion control. The aim was to assess two different open-toe sandals on postural stability in people with rheumatoid arthritis.

Methods

Twenty women with rheumatoid arthritis were assessed in quiet standing under four conditions: (1) open-back sandal; (2) closed-back sandal; (3) own footwear and (4) bare feet. Postural stability was assessed as postural sway in the anterior-posterior and medial-lateral directions, with eyes open and eyes closed, using a pressure mat. Repeated measures analysis of variance tested the interaction effect of the footwear and eye conditions on anterior-posterior and medial-lateral sway.

Findings

In eyes-open, there was no significant difference in anterior–posterior sway (P = .169) and medial-lateral sway (P = .325) for footwear conditions. In eyes-closed testing, compared with barefoot conditions, increased anterior–posterior sway was observed with participants' footwear (P < .0001), the open-back sandal (P = .005), and the closed-back sandal (P = .017). With eyes closed, increased anterior–posterior sway was also observed with the participants' footwear compared with the closed-back sandal (P = .041). Increased medial-lateral sway was observed with the closed-back sandal compared with bare feet (P = .014).

Interpretation

Sandals may be detrimental to older women with well-established rheumatoid arthritis when eyes are closed. Further investigation is needed to evaluate the effect of sandals on dynamic tasks.     

In vitro biomechanical evaluation of fibular movement in below knee amputations

Background

In below knee amputations, the remaining fibula may be subjected to abnormal forces resulting in problematic tibia-fibular movement. The purpose of the current work was to examine the effect of amputation length and interosseous membrane integrity on fibular movement when subjected to unopposed biceps femoris muscle tension.

Methods

Forty embalmed cadaveric specimens were subjected to a below knee amputation with fibular lengths of 5 cm and 10 cm. A subset of specimens (n = 20) was further modified by sectioning the interosseous membrane. The tibias were mounted in a material testing machine and the biceps femoris was sutured to the actuator. Position-controlled tensile cyclic loading was applied (initial displacement of 4 mm for 100 cycles at 0.5 Hz with increments of 2 mm up to 20 mm) to the biceps femoris. The kinematics of the fibula with respect to the tibia was analyzed for three degrees of freedom: abduction, flexion and rotation.

Findings

There was no interaction between below knee amputation length and interosseous membrane integrity on the degree of abduction, flexion, and rotation. However, below knee amputations with a sectioned interosseous membrane are abducted to a significantly greater degree than intact interosseous membrane below knee amputations. Furthermore, although embalmed specimens were tested here, embalming was consistent across specimens and it is unlikely that this confounded the findings.

Interpretation

Understanding the cause of fibular abduction in below knee amputation will lead to recommendations for preventive surgical and rehabilitative measures.     

Speed effect of selected Tai Chi Chuan movement on leg muscle activity in young and old practitioners

Background

Tai Chi Chuan is becoming a popular exercise for improving balance and preventing falls in the elderly. To date, there is no quantitative study investigating the effect of Tai Chi Chuan movement speed on leg muscle function. This study investigated the effect of Tai Chi Chuan exercise performed at different speed on leg muscle activity characteristics in both young and old Tai Chi Chuan practitioners.

Methods

Surface electromyography of six leg muscles and kinematics of lower extremity joints were measured in young and old subjects during Tai Chi Chuan practice at fast, normal, and slow speed, respectively. The magnitude and duration of activation, and durations of isometric, concentric and eccentric actions of each muscle were compared among three speeds and between two groups.

Findings

The activation duration of all six leg muscles was significantly longer at slower speed than at faster speed (P < 0.039). The durations of isometric, concentric and eccentric actions were either longer at the slower speed or did not change with speed for all six leg muscles. The action of knee extensor was primarily isometric at slower speed (P = 0.004), and increased significantly to concentric and eccentric at faster speed (P < 0.031). The activation magnitude of posterior leg muscles increased with speed (P < 0.009). The old subjects had significantly shorter activation duration and lower activation magnitude in several leg muscles than the young, but similar speed effect as the young.

Interpretation

The activation duration and function of leg muscles, especially the knee extensor muscle, are significantly affected by the speed of the selected Tai Chi Chuan movement. Practicing Tai Chi Chuan at different speed may alter the role of muscular function in movement control.     

Effects of fatiguing treadmill running on sensorimotor control in athletes with and without functional ankle instability

Background

Sensorimotor control is permanently impaired following functional ankle instability and temporarily decreased following fatigue. Little is known on potential interactions between both conditions. The purpose was to investigate the effect of fatiguing exercise on sensorimotor control in athletes with and without (coper, controls) functional ankle instability.

Methods

19 individuals with functional ankle instability, 19 ankle sprain copers, and 19 non-injured controls participated in this cohort study. Maximum reach distance in the star excursion balance test, unilateral jump landing stabilization time, center of pressure sway velocity in single-leg-stance, and passive ankle joint position sense were assessed before and immediately after fatiguing treadmill running. A three factorial linear mixed model was specified for each outcome to evaluate the effects of group, exhausting exercise (fatigue) and their interactions (group by fatigue). Effect sizes were calculated as Cohen's d.

Findings

Maximum reach distance in the star excursion balance test, jump stabilization time and sway velocity, but not joint position sense, were negatively affected by fatigue in all groups. Effect sizes were moderate, ranging from 0.27 to 0.68. No significant group by fatigue interactions were found except for one measure. Copers showed significantly larger prefatigue to postfatigue reductions in anterior reach direction (P ≤ 0.001; d = − 0.55) compared to the ankle instability (P = 0.007) and control group (P = 0.052).

Interpretation

Fatiguing exercise negatively affected postural control but not proprioception. Ankle status did not appear to have an effect on fatigue-induced sensorimotor control impairments.     

Experimental calf muscle pain attenuates the postural stability during quiet stance and perturbation

Background

The purpose of this study was to evaluate how acute pain changes the postural control and stability during quiet standing and after unexpected perturbations.

Methods

Nine subjects stood as quiet as possible on a movable force platform that recorded the centre of pressure position and provided unexpected floor perturbations, before, during and after experimental calf muscle pain. Bilateral surface electromyography from the tibialis anterior and medial gastrocnemius muscles was recorded. The foot pressure distributions were measured using pressure insoles. Intramuscular injections of hypertonic saline were administrated (right leg) to induce acute pain in the tibialis anterior and/or medial gastrocnemius muscles, and an isotonic injection was used as control.

Findings

Simultaneous pain in tibialis anterior and medial gastrocnemius altered the postural control. During quiet standing: higher medial-lateral centre of pressure speed and increased total sway displacement (P < 0.05), weight moved to the non-painful side, (P < 0.05) and plantar centre of pressure of the left foot was shifted towards the heel’s direction (P < 0.05). During forward perturbation: higher mean displacement in the medial-lateral direction (P < 0.05). After the perturbation: larger sway area (P < 0.05). Pain only in the medial gastrocnemius muscle increased medial-lateral centre of pressure speed (P < 0.05) during the quiet standing. Pain only in the tibialis anterior muscle increased peak pressure on the contralateral foot (P < 0.05).

Interpretation

These findings suggest that large acute painful areas on the calf muscles impair the postural control and potentially increase the risk factors for falls. Further strategies aiming to reduce pain in patients may lead to improvement in balance.     

Effect of postoperative physical training on activity after curative surgery for non-small cell lung cancer: a multicentre randomised controlled trial

Objective

To evaluate the effect of a combined hospital plus home exercise programme following curative surgery for non-small cell lung cancer (NSCLC).

Design

Randomised controlled trial.

Setting

Teaching hospital.

Participants

One hundred and thirty-one subjects with NSCLC admitted for curative surgery.

Interventions

Participants were randomised to usual care or a hospital plus home exercise programme.

Outcomes

The primary outcome was the between-group difference in physical activity 4 weeks after surgery. Secondary outcomes were the difference in quadriceps strength, exercise tolerance and quality of life [Short Form-36 (SF-36) and European Organisation for Research and Treatment of Cancer (EORTC) QLQ-LC13] from pre-operatively (baseline) to 4 weeks after surgery.

Results

The participants (n = 131) had a mean age of 68 [standard deviation (SD) 11] years and mean forced expiratory volume in 1 second of 2.4 (SD 1.1) l. There were no significant differences in physical activity between the groups 4 weeks after surgery [mean difference adjusted for baseline 12 minutes/day, 95% confidence interval (CI) −20.2 to 44.1]. In addition, there were no significant differences in total SF-36 or EORTC QLQ-LC13 scores from baseline to 4 weeks after surgery. Both groups had recovered their pre-operative walking distance 4 weeks after surgery, and there were no differences between the groups (mean difference in Incremental Shuttle Walk Test from baseline to 4 weeks after surgery (−26 m, 95% CI −94.2 to 42.3).

Conclusions

A hospital plus home exercise programme showed little benefit in unselected patients with NSCLC following surgery. Regardless of group allocation, the patients had recovered their pre-operative exercise tolerance levels by 4 weeks after surgery.     

Exercise is a potent stimulus for enhancing circulating DNase activity

Objectives

To elucidate cell free DNA (cfDNA) clearance kinetics following an acute bout of high intensity exercise by measuring circulating DNase activity reduction (AR).

Design and methods

Serum cfDNA concentration and DNase-AR were measured prior to and post (immediately post, 7 and 30 min post) an acute bout of rowing exercise until exhaustion.

Results

Serum cfDNA concentration was significantly (P ≤ .001) elevated immediately post (2.5-fold) and 7 min post exercise (2.3-fold) with a return close to baseline at 30 min post exercise (1.5-fold). The rise in cfDNA was accompanied by a concomitant, significant (P ≤ .001) decrease in serum DNase-AR from 15.1% prior to exercise to 3.1% AR at cessation of the exercise test and 7 min post exercise (3.9% AR). DNase-AR returned close to baseline at 30 min post exercise (5.2% AR).

Conclusions

A single bout of high intensity exercise is a potent stimulus for enhancing circulating DNase activity in healthy people. Acute exercise may therefore be considered as a non-pharmacological stimulus to trigger DNase activity.This finding may be relevant for pathological conditions associated with increased cfDNA concentrations like cystic fibrosis, where pharmacological recombinant human DNase (rhDNase) treatment has been successfully used to improve patients' health and physical function.     

La rééducation d'emblée des ischiojambiers après chirurgie du DIDT

Introduction

Following knee ligamentoplasty, the task of muscle restoration principally focuses on the hamstrings, which are the only active structure which can protect the graft and prevent detachment. However, specialists generally advise against work on these muscles for a period of 3–6 weeks following semi-tendinosus and gracilis surgery. The hamstrings are thus left resting during this period, which encourages their wasting and tightening.

Objective

Our team, guided by the principles of rehabilitation for muscular problems, has for more than 2 years been strengthening the hamstrings immediately following ligamentoplasty surgery, making use of the semi-tendinous and gracilis. The objective is not only muscle performance and the protection of the graft, but above all encouraging the healing of the semi-tendinous and gracilis in order to align the collagen fibres and improve their mechanical resistance.

Content

It is a single-focus study, continually rolled forward. This protocol was practised on 56 patients, two patients having to withdraw from the programme because of strain problems.

Methodology

During the hospitalisation of the patient, concentric contraction of the knee flexors was engendered using weak resistance operated manually. Later in our rehabilitation centre, our patients exercised in a hamstring « chair », in the eccentric mode below maximum charge, with an increasing load progression. This was done daily up to the sixth week.

Results

Our results, at the 3rd and 6th week post-surgery, showed a favourable change in articular amplitude and pain suffered, with a low rate of complications. Evidence of pain was found in 12.5% of cases (7/56). Of these 7 patients, 2 (3.5%) had incidents involving muscular strain, rendering the interruption of the physiotherapy necessary for more than 3 consecutive days. Isokinetic results carried out at 4.6 ± 0.7 months showed excellent muscular recuperation of the hamstrings with a deficit of 9.6 ± 14% at slow speed and of 6.8 ± 13.1% at fast speed compared with the heterolateral side.

Discussion

The number of painful occurrences in our study, at 12.5%, is lower than the 20% ad higher frequently found in other documented cases. However the definition of these painful occurrences is imprecise. The performance deficit of hamstrings measured by isokinetic tests after 6 months varied between 15 and 20% depending upon the published study. In our study the results at 4.6 months were better (< 10%).

Conclusion

There can no longer be any doubt about the benefits of strengthening the hamstrings in pathologies of an anterior cruciate ligament. Our work has shown that the early strengthening of these muscles is not disadvantageous. On the contrary we believe that our policy promotes the patient's muscular and functional recovery.     

Leg preference associated with protective stepping responses in older adults

Background

Asymmetries in dynamic balance stability have been previously observed. The goal of this study was to determine whether leg preference influenced the stepping response to a waist-pull perturbation in older adult fallers and non-fallers.

Methods

39 healthy, community-dwelling, older adult (> 65 years) volunteers participated. Participants were grouped into non-faller and faller cohorts based on fall history in the 12 months prior to the study. Participants received 60 lateral waist-pull perturbations of varying magnitude towards their preferred and non-preferred sides during quiet standing. Outcome measures included balance tolerance limit, number of recovery steps taken and type of recovery step taken for perturbations to each side.

Findings

No significant differences in balance tolerance limit (P ≥ 0.102) or number of recovery steps taken (η²_partial ≤ 0.027; P ≥ 0.442) were observed between perturbations towards the preferred and non-preferred legs. However, non-faller participants more frequently responded with a medial step when pulled towards their non-preferred side and cross-over steps when pulled towards their preferred side (P = 0.015).

Interpretation

Leg preference may influence the protective stepping response to standing balance perturbations in older adults at risk for falls, particularly with the type of recovery responses used. Such asymmetries in balance stability recovery may represent a contributing factor for falls among older individuals and should be considered for rehabilitation interventions aimed at improving balance stability and reducing fall risk.     

Vestibular Deficits Leading to Disequilibrium and Falls in Ambulatory Amyotrophic Lateral Sclerosis

Objective

To assess vestibular deficits in response to disequilibrium in ambulatory individuals with amyotrophic lateral sclerosis (ambALS).

Design

All participants completed standard protocols for the Sensory Organization Test (SOT) by computerized dynamic posturography.

Setting

Multidisciplinary amyotrophic lateral sclerosis clinic at an academic medical center.

Participants

Study participants (N=34) consisted of ambALS (n=19) and healthy controls (HC) (n=15).

Interventions

Not applicable.

Main Outcome Measures

Equilibrium scores (ESs) obtained from averaged sway amplitude in condition 5 (ES5) and condition 6 (ES6) of the SOT.

Results

In conditions of altered somatosensory information with vision absent or vision sway-referenced, the mean ± SD scores for ambALS (ES5=51.4±22.5; ES6=50.8±22.1) were lower than those for HC (ES5=65.4±11.7, P≤.03; ES6=58.9±12.5, P>.05). Seven ambALS (37%) experienced a total of 19 falls during the sway-referenced support test conditions. There were no falls in the HC.

Conclusions

Nearly 37% of ambALS with normal clinical balance testing have decreased ability to use the vestibular input and required increased reliance on visual input for postural orientation to sustain equilibrium. The mechanism of this alteration in sensory preference is not completely clear. Extrapyramidal involvement early in ALS may be indicated.     

Effect of hip protectors,falling angle and body mass index on pressure distribution over the hip during simulated falls

Background

We examined how a soft shell hip protector affects the magnitude and distribution of force to the hip during simulated falls, and how the protective effect depends on the fall direction and the amount of soft tissue padding over the hip.

Methods

Fourteen young women with either high or low body mass index participated in a “pelvis release experiment” that simulated falls resulting in either lateral, anterolateral or posterolateral impact to the pelvis with/without a soft shell hip protector. Outcome variables were the magnitude and location of peak pressure (d, theta) with respect to the greater trochanter, total impact force, and percent force applied to four defined hip regions.

Findings

The soft shell hip protector reduced peak pressure by 70%. The effect was two times greater in low than high body mass index individuals. The protector shunted the peak pressure distally along the shaft of the femur (d = 52 mm (SD 22), theta = −21° (SD 49) in the unpadded trials versus d = 81 mm (SD 23), theta = −10° (SD 35) in the padded trials). Peak force averaged 12% greater in posterolateral and 17% lower in anterolateral than lateral falls.

Interpretation

Our results indicate that the hip protector we tested had a much stronger protective benefit for low than high body mass index individuals. Next generation protectors might be developed for improved shunting of pressure away from the femur, improved protection during posterolateral falls, and greater force attenuation for low body mass index individuals.     

Trunk muscle involvement is most critical for the loss of balance control in patients with facioscapulohumeral muscular dystrophy

Background

Although it is known that muscle weakness is a major cause of postural instability and leads to an increased incidence of falls in patients with neuromuscular disease, the relative contribution of lower extremity and trunk muscle weakness to postural instability has not been studied well.

Methods

We determined the relationship between muscle fatty infiltration and sagittal-plane balance in ten patients with facioscapulohumeral muscular dystrophy. Sagittal-plane platform translations were imposed in forward and backward directions on patients with facioscapulohumeral muscular dystrophy and healthy controls. Stepping thresholds were determined and kinematic responses and center-of-mass displacements were assessed using 3 dimensional motion analysis. In the patients, magnetic resonance imaging was used to determine the amount of fatty infiltration of trunk and lower extremity muscles.

Findings

Stepping thresholds in both directions were decreased in patients compared to controls. In patients, significant correlations were found for fatty infiltration of ventral muscles with backward stepping threshold and for fatty infiltration of dorsal muscles with forward stepping threshold. Fatty infiltration of the rectus abdominis and the back extensors explained the largest part of the variance in backward and forward stepping thresholds, respectively. Center-of-mass displacements were dependent on intensity and direction of perturbation. Kinematic analysis revealed predominant ankle strategies, except in patients with lumbar hyperlordosis.

Interpretation

These findings indicate that trunk muscle involvement is most critical for loss of sagittal-plane postural balance in patients with facioscapulohumeral muscular dystrophy. This insight may help to develop rehabilitation strategies to prevent these patients from falling.     

Ankle positioning and knee perturbation affect temporal recruitment of the vasti muscles in people with patellofemoral pain

Objectives

To compare the temporal recruitment of the vastus medialis obliquus (VMO) and vastus lateralis (VL) during voluntary ankle movements and perturbed standing in people with patellofemoral pain, and to determine the effects of different reflex and voluntary postural exercise tasks on VMO facilitation.

Design

Repeated-measures design.

Participants

Twenty-three subjects with patellofemoral pain.

Interventions

Quadriceps reflex contraction in response to postero-anterior knee perturbations was measured with three crural muscle contraction conditions and three postural exercises (semi-squatting, tip-toeing and heel standing).

Main outcome measures

The electromyographic (EMG) onset time of the VMO and VL during each task was measured and compared across the different tasks.

Results

The mean EMG onset time of the VMO was later than that of the VL in the voluntary tasks such as tip-toeing (VMO 95.3 ms vs VL 36.4 ms, mean difference 58.9 ms, 95% confidence interval −33.7 to 151.5 ms), whereas earlier VMO activation was found in the perturbation tests such as toe standing (VMO 17.6 ms vs VL 22.9 ms, mean difference −5.3 ms, 95% confidence interval −25.3 to 14.7 ms).

Conclusion

These findings suggest the potential benefits of unexpected perturbation activities for facilitating VMO activation. The clinical applications of perturbation tasks in rehabilitation exercise programmes and the underlying mechanisms warrant further investigation.