Sway-referenced Support Surface Research Articles

Increased roll tilt thresholds are associated with subclinical postural instability in asymptomatic adults aged 21 to 84 years.

Balance assessments that intentionally alter the reliability of visual and proprioceptive feedback (e.g., standing on foam with eyes closed) have become a standard approach for identifying vestibular mediated balance dysfunction in older adults. However, such assessments cannot discern which specific element of the vestibular system (e.g., semicircular canal, otolith, or combined canal-otolith) underlies the observed age-related changes in balance performance. The present study was designed to determine the associations between specific sources of vestibular noise and quantitative measures of quiet stance postural control measured during standard "vestibular" balance conditions. A group of 52 asymptomatic adults (53.21 ± 19.7, 21 to 84 years) without a history of vestibular or neurologic disorders volunteered for this study. We measured a battery of five vestibular perceptual thresholds that assay vestibular noise with predominant contributions from the vertical canals, lateral canals, utricles, saccules, and the centrally integrated canal-otolith signal. In addition, participants completed two standard balance assessments that were each designed to prioritize the use of vestibular cues for quiet stance postural control-eyes closed on foam (Condition 4 of the Modified Romberg Balance Test) and eyes closed, on a sway referenced support surface (Condition 5 of the Sensory Organization Test). In age adjusted models, we found strong positive associations between roll tilt vestibular thresholds, a measure of noise in the centrally integrated canal-otolith signal, and the root mean square distance (RMSD) of the anteroposterior and mediolateral center of pressure (CoP) captured during eyes closed stance on a sway referenced support surface. The strength of the association between roll tilt thresholds and the RMSD of the CoP was between 3-times and 30-times larger than the association between postural sway and each of the other vestibular thresholds measured. We posit that noise in the centrally estimated canal-otolith "tilt" signal may be the primary driver of the subclinical postural instability experienced by older adults during the "vestibular" conditions of balance assessments. Additional testing in adults with clinical balance impairment are needed to identify if roll tilt thresholds may also serve as a surrogate metric by which to detect vestibular mediated balance dysfunction and/or fall risk.

Sensory Integration for Postural Control in Rheumatoid Arthritis Revealed by Computerized Dynamic Posturography

Rheumatoid arthritis (RA) is a systemic autoimmune disease that impairs mobility. How does sensory information influence postural responses in people with RA? The aim of this study was to evaluate the postural control of people with RA during a sensory organization test, comparing how sensory information influences postural responses in people with rheumatoid arthritis compared with healthy people. Participants were 28 women with rheumatoid arthritis (RA group) and 16 women without any rheumatoid disease (Control group CG). The Sensory Organization Test (SOT) was performed on a Smart Balance Master® (NeuroCom International, Inc., Clackamas, OR, USA) and center of pressure (COP) was measured. SOT conditions: SOT1 (eyes open, fixed support surface and surround; SOT2) eyes closed, fixed support surface and surround; and SOT5) eyes closed, sway-referenced support surface, and fixed surround. To compare the demographic and clinical aspects between groups, independent t-test or Mann-Whitney's U-test were used. Differences were found between groups. Between SOT conditions, for CG and RA, COP was faster for SOT-5 than SOT-1, while SOT-1 and SOT-2 presented similar COP velocity. For SOT-2 and SOT-5, COP was larger for the RA group. For both groups, SOT-1 presented the smallest COP, and SOT-5 showed the largest COP.

Sensory Reliance And Visual Fixation In Individuals With And Without Multiple Ankle Sprains

Individuals with a history of multiple ankle sprains (IMAS) present rigid movement patterns contributing to postural instability. Evidence indicates that IMAS upregulate reliance on visual feedback as a compensatory mechanism for postural stability. Increased visual reliance may require IMAS to fixate gaze (visual fixation) on fewer objects. However, how vision is utilized with IMAS while performing static and dynamic tasks compared to healthy controls is unknown. PURPOSE: To validate differences in visual reliance and examine visual fixation while controlling posture in injured-limb in individuals with and without MAS. We hypothesized that IMAS will upregulate visual reliance and increase visual fixation while maintaining posture in injured-limb compared to healthy controls. METHODS: Ten physically active individuals with and without MAS completed the Sensory Organization Test (SOT) to compute sensory ratios that measure reliance on primary sensory systems (somatosensory, visual, vestibular) during postural control. The SOT comprises six conditions to challenge somatosensory, visual, and vestibular feedback in a combination of the sway-referenced support surface and visual surroundings with and without vision. Healthy controls were matched to IMAS and assigned an injured-limb. Visual fixation was measured with gaze fixation count using EyeNal software. One-way repeated measures ANOVA (alpha = .05) and Cohen’s d effect size (ES) analyzed group comparisons. RESULTS: IMAS significantly upregulated vestibular reliance compared to healthy controls (IMAS = .78 ± .02, Healthy = .68 ± .09, ES = 1.44, P = .037), and a large ES was found on visual reliance (IMAS = .96 ± .02, Healthy = .93 ± .05, ES = .79) while controlling posture in injured-limb. No significant group differences were found for visual fixation (P > .05). However, a large ES was found for visual fixation for the SOT condition 1 where all three sensory feedback was intact (IMAS = 14 ± 7.80, Healthy = 21 ± 9.73, ES = .79). CONCLUSIONS: The preliminary results partially confirmed our hypothesis. IMAS upregulated vestibular reliance to aid visual feedback to control posture. Increased visual fixation in IMAS may be indicative of limiting gaze boundaries to obtain accurate visual feedback, but a larger sample size is necessary to confirm our hypothesis.

Adaptations from the prosthetic and intact limb during standing on a sway-referenced support surface for transtibial prosthesis users

Purpose: To investigate the bilateral postural adaptations as a result of standing on an increasingly unstable sway-referenced support surface with both the intact and prosthetic limb for transtibial prosthesis users (TPUs).Method: TPUs (n = 14) and matched controls (n = 14) stood quietly in multiple foot placement conditions (intact foot, prosthetic foot and both feet) on a sway-referenced support surface which matched surface rotation to the movement of the centre of pressure (CoP). Force and motion data were collected and used to analyse CoP mean position, displacement integral and force components under intact and prosthetic limbs.Results: Significant differences were found between prosthesis users and controls in CoP mean position in anteroposterior (1.5 (95% CI, 1.2–1.8) cm) and mediolateral directions (3.1 (95% CI, 0.5–5.7) cm. CoP displacement integrals were significantly different greater for prosthesis user group in the anteroposterior direction. Force components differences were found in all planes (anteroposterior: 0.6 (95% CI, 0.4–0.8 N); mediolateral: 0.1 (95% CI, 0.0–0.2 N & 0.3 (95% CI, 0.2–0.4) N, inferosuperior: 2.2 (95% CI, 1.4–3.0) N).Conclusions: TPUs have bilateral static and dynamic postural adaptations when standing on a sway-referenced support surface that is different to controls, and between prosthetic and intact sides. Results further support evidence highlighting importance of the intact limb in maintenance of postural control in prosthesis users. Differences indicate clinical treatment should be directed towards improving outcomes on the intact side.Implications for rehabilitationProsthesis users have bilateral adaptations when standing on a sway referenced support surfaceThese adaptations are different to controls, and between prosthetic and intact sides.The intact limb is the major contributor to maintenance of postural control in prosthesis users.Clinical treatment should account for this when interventions are designed.

Cortical control of upright stance in elderly

This study examined differences between young and elderly volunteers in cortical involvement to human posture control during quiet stance with normal and altered sensory stimulation (Experiment-1), and biomechanical perturbations (Experiment-2). The primary focus of the first part was to monitor changes in cortical activity when unexpectedly altering the sensory conditions of upright stance, such as switching from stable (eyes open, fixed support surface) to less-stable (eyes closed, sway-referenced support surface) conditions. Our results demonstrate increased cortical activations in delta (0.2–4 Hz) and gamma (30–50 Hz) oscillations, primarily over central-frontal, central, and central parietal cortices during challenging postural conditions. While increased delta rhythms were observed in both groups during challenging sensory conditions, elderly individuals also showed increased gamma band activity over sensorimotor and parietal cortices, when compared to the younger group. To our knowledge, this study is the first to show age differences in balance related cortical activations during continuous postural tasks with challenging sensory conditions. Preliminary correlations also suggest that increased cerebral activity became more relevant to the control of Center of Mass (COM) dynamics when upright stance is threatened. The results of Experiment-2 also showed for the first time that oscillatory rhythms of the cortex are coherent with muscle firing characteristics suggesting increased corticospinal drive from leg motor cortex to lower limb motoneurons following postural perturbations. Finally, perturbation evoked potential (PEP) analyses suggest that, rather than motor system malfunctioning, impairments in perceptual processing of sensory afference forms the basis of prolonged muscle response delays during perturbed balance in the elderly.

Computerized dynamic posturography for postural control assessment in patients with intermittent claudication.

Computerized dynamic posturography with the EquiTest is an objective technique for measuring postural strategies under challenging static and dynamic conditions. As part of a diagnostic assessment, the early detection of postural deficits is important so that appropriate and targeted interventions can be prescribed. The Sensory Organization Test (SOT) on the EquiTest determines an individual's use of the sensory systems (somatosensory, visual, and vestibular) that are responsible for postural control. Somatosensory and visual input are altered by the calibrated sway-referenced support surface and visual surround, which move in the anterior-posterior direction in response to the individual's postural sway. This creates a conflicting sensory experience. The Motor Control Test (MCT) challenges postural control by creating unexpected postural disturbances in the form of backwards and forwards translations. The translations are graded in magnitude and the time to recover from the perturbation is computed. Intermittent claudication, the most common symptom of peripheral arterial disease, is characterized by a cramping pain in the lower limbs and caused by muscle ischemia secondary to reduced blood flow to working muscles during physical exertion. Claudicants often display poor balance, making them susceptible to falls and activity avoidance. The Ankle Brachial Pressure Index (ABPI) is a noninvasive method for indicating the presence of peripheral arterial disease and intermittent claudication, a common symptom in the lower extremities. ABPI is measured as the highest systolic pressure from either the dorsalis pedis or posterior tibial artery divided by the highest brachial artery systolic pressure from either arm. This paper will focus on the use of computerized dynamic posturography in the assessment of balance in claudicants.

Effects of Intensive Whole-Body Vibration Training on Muscle Strength and Balance in Adults With Chronic Stroke: A Randomized Controlled Pilot Study

ObjectivesTo investigate the effects of a 6-week whole body vibration (WBV) training program in patients with chronic stroke. DesignRandomized controlled pilot trial with 6 weeks' follow-up. SettingUniversity hospital. ParticipantsAdults with chronic stroke (N=15) were randomly assigned to an intervention (n=7) or a control group (n=8). InterventionsSupervised, intensive WBV training. The vibration group performed a variety of static and dynamic squat exercises on a vibration platform with vibration amplitudes of 1.7 and 2.5mm and frequencies of 35 and 40Hz. The vibration lasted 30 to 60 seconds, with 5 to 17 repetitions per exercise 3 times weekly for 6 weeks. Participants in the control group continued their usual activities and were not involved in any additional training program. Main Outcome MeasuresThe primary outcome variable was the isometric and isokinetic muscle strength of the quadriceps (isokinetic dynamometer). Additionally, hamstrings muscle strength, static and dynamic postural control (dynamic posturography), and muscle spasticity (Ashworth Scale) were assessed. ResultsCompliance with the vibration intervention was excellent, and the participants completed all 18 training sessions. Vibration frequencies of both 35 and 40Hz were well tolerated by the patients, and no adverse effects resulting from the vibration were noted. Overall, the effect of intensive WBV intervention resulted in significant between-group differences in favor of the vibration group only in isometric knee extension strength (knee angle, 60°) (P=.022) after 6 weeks of intervention and in isokinetic knee extension strength (velocity, 240°/s) after a 6-week follow-up period (P=.005), both for the paretic leg. Postural control improved after 6 weeks of vibration in the intervention group when the patients had normal vision and a sway-referenced support surface (P<.05). Muscle spasticity was not affected by vibration (P>.05). ConclusionsThese preliminary results suggest that intensive WBV might potentially be a safe and feasible way to increase some aspect of lower limb muscle strength and postural control in adults with chronic stroke. Further studies should focus on evaluating how the training protocol should be administered to achieve the best possible outcome, as well as comparing this training protocol to other interventions.

Posturography and locomotor tests of dynamic balance after long-duration spaceflight

The currently approved objective clinical measure of standing balance in astronauts after space flight is the Sensory Organization Test battery of computerized dynamic posturography. No tests of walking balance are currently approved for standard clinical testing of astronauts. This study determined the sensitivity and specificity of standing and walking balance tests for astronauts before and after long-duration space flight. Astronauts were tested on an obstacle avoidance test known as the Functional Mobility Test (FMT) and on the Sensory Organization Test using sway-referenced support surface motion with eyes closed (SOT 5) before and six months after (n=15) space flight on the International Space Station. They were tested two to seven days after landing. Scores on SOT tests decreased and scores on FMT increased significantly from pre- to post-flight. In other words, post-flight scores were worse than pre-flight scores. SOT and FMT scores were not significantly related. ROC analyses indicated supra-clinical cut-points for SOT 5 and for FMT. The standard clinical cut-point for SOT 5 had low sensitivity to post-flight astronauts. Higher cut-points increased sensitivity to post-flight astronauts but decreased specificity to pre-flight astronauts. Using an FMT cut-point that was moderately highly sensitive and highly specific plus SOT 5 at the standard clinical cut-point was no more sensitive than SOT 5, alone. FMT plus SOT 5 at higher cut-points was more specific and more sensitive. The total correctly classified was highest for FMT, alone, and for FMT plus SOT 5 at the highest cut-point. These findings indicate that standard clinical comparisons are not useful for identifying problems. Testing both standing and walking balance will be more likely to identify balance deficits.

Spatial orientation during eyes closed versus open in the dark: Are they the same?

We hypothesized that keeping one’s balance with eyes open in the dark is different and more difficult than eyes closed because the brain continues to process visual inputs in the dark when the eyes are open. On the other hand, when the eyes are closed, the visual system does not signal incongruent information with which the brain must compare the other sensory systems. A variety of cognitive (subtracting backwards by seven as quickly and accurately as possible) and support surface (fixed versus sway-referenced) conditions were used to probe the neural mechanisms underlying the sensory organization processes in healthy young adults. Peak-to-peak anteroposterior sway performance revealed two dissociated components of the treatment effects. The first component came from the visuospatial factor. Balance control during eye closure and eyes open in the dark were found to be similar but poorer than baseline condition (eyes open under typical lighting). The second component was the effect of task difficulty in which balance control in the sway-referenced condition was worse compared to fixed support during eye closure or eyes open in the dark. Analyses of the cognitive performance also revealed different underlying neural mechanisms of the experimental conditions. Subtraction speed under the fixed support surface condition was similar among all the conditions but was faster with eyes closed during the sway-referenced support surface condition. Accuracy was not affected among the visual and surface conditions. We conclude that sensory processing load with eyes closed is lower than eyes open in the dark, thereby allowing cognitive performance to proceed more efficiently. Performing a difficult subtraction task with eyes closed may afford a decrease in dual-task interference since similar brain areas, particularly the parietal region, are involved in both tasks. The results are discussed with reference to clinical application and spatial disorientation in aviation.

Sensorimotor specificities in balance control of expert fencers and pistol shooters

Motor skills during sport activity are influenced by practice-related constraints and leads to the development of appropriate postural sensorimotor strategies. Fencing is highly requiring visual monitoring and high-speed motor skills while retaining efficient balance control. Conversely, pistol shooting is a static activity requiring a high control of body sway. This study aimed to evaluate balance control and the related neurosensory organisation through reproducible postural tasks with and without sensory conflict. Twelve expert fencers, 10 expert shooters and 10 sedentary controls have performed a static posturographic test and a sensory organisation test (in 6 different sensory situations based upon sway-referenced vision and support surface, C1 to C6). Shooters yielded a better balance control during C1 (eyes open) and C2 (eyes closed) than fencers and controls. Fencers showed a better balance control in C5 (eyes closed with sway-referenced support surface) than shooters and controls. While this study confirms the beneficial effects of physical activities on balance control, a differential effect on balance characteristics due to the acquired specific motor skills was also noted. In addition to high proprioceptive sensitivity in sportsmen, dynamic constraints in fencing force fencers to permanently select the most relevant information to manage better sensory conflicting situations.

Postural stability in altered and unaltered sensory environments following fatiguing exercise of lower extremity joints

Investigations of postural recovery following controlled external perturbations have provided models for healthy and pathological balance behavior. Less work, however, has investigated postural responses related to internal perturbations of the balance system. In this study, lower extremity joint (knee, or ankle) and overall fatigue of the dominant leg provided the internal perturbations to the balance system. Postural sway was examined during unilateral dominant leg standing before and immediately following fatiguing exercise, as well as at 10, 20, and 30 min post-fatigue activity. Sway was measured in both firm and sway-referenced support surface (external perturbation) conditions. Both joint-localized fatigue and overall fatigue were found to induce impairments in postural control, which were further exacerbated by external postural perturbations. Follow-up pairwise comparisons indicated that these impairments persisted at 10 and 30 min post-fatigue. No differences in postural sway were found between fatigue locations or across any interactions between sway and fatigue location. The results indicated that muscular fatigue imposed a prolonged internal perturbation to postural control, regardless of any individual or combined joint fatigue localization. This global effect, combined with the prolonged impairment in postural response, provides support for critical contributions from a central mechanism to postural deficits due to fatigue.

Head sway response to optic flow: Effect of age is more important than the presence of unilateral vestibular hypofunction

The purpose of this study was to examine how older adults with vestibular impairment use sensory feedback for postural control. Nine older adult subjects with unilateral vestibular hypofunction (UVH, mean age 69 y) and 14 older (mean age 70 y) and 8 young adult controls (CON, mean age 28 y) viewed full-field optic flow scenes while standing on a fixed or sway-referenced support surface. The subjects with UVH had 100% caloric asymmetry. Optic flow consisted of sinusoidal anterior-posterior movement of the visual surround at three frequencies and three amplitudes of stimulation. The anterior-posterior head sway was measured. The number of head sway responses that were coupled to the optic flow and magnitude of head sway during optic flow relative to during quiet stance on fixed floor was quantified. The number of trials in which the head sway response was significantly coupled to the optic flow was significantly greater in the Older UVH and Older CON subjects compared with the Young CON subjects. Furthermore, the magnitude of head sway was two to three times greater in Older UVH and CON compared with Young CON subjects. There was no difference in coupling or magnitude of head sway between Older UVH and Older CON subjects. The amplitude of sway was also dependent on the amount of surface support, stimulus frequency, and stimulus amplitude. Older adults with unilateral vestibular hypofunction who are able to effectively compensate show no difference in postural responses elicited by optic flow compared with age-matched controls.

Computerized posturography balance assessment of patients with bilateral ventralis intermedius nuclei deep brain stimulation

Bilateral ventralis intermedius nuclei (Vim) deep brain stimulation (DBS) improves tremor in patients with both essential tremor (ET) and Parkinson's disease (PD). In each condition, patients have individually noted both subjective improvement and worsening in balance. Computerized posturography (CP) is able to quantify some aspects of balance. Twenty-one patients (8 with PD and 13 with ET) with bilateral Vim DBS were recruited to undergo randomized-order identical CP testing (EquiTest system) while their DBS devices were both activated and deactivated. One PD patient could not complete any OFF assessment and is not included. Three PD patients could not tolerate portions of the OFF testing. Overall, sensory organization testing was improved by DBS activation in conditions that involved quiet standing with eyes open with no motion of the support surface, or with sway-referenced support surface motion, but worsened during quiet standing with eyes closed only in ET patients. Falls lessened with activation in ET patients. Motor control testing was not changed. Bilateral Vim DBS activation mostly improved balance, but may modestly worsen other specific features.

Assessment of a Practice Effect in Serial Sensory Organization Testing Scores of Healthy Adults

This study assessed whether a practice effect occurs across five serial administrations of the sensory organization test. Composite equilibrium scores and mean equilibrium scores from 30 healthy volunteers (M age=36.9, SD = 12.2 yr.) performing each of the six test conditions were examined using a two-way repeated-measures analysis of variance. Analysis yielded a significant interaction between testing condition and time, as well as significant main effects for both condition and time. Pairwise comparisons showed significant differences among test conditions and the first and second times of test administration. Analysis of simple effects between the two administrations identified significant increases in composite equilibrium scores and mean equilibrium scores on two sway-referenced support surface conditions, vision removed and sway-referenced visual surround. An immediate increase in equilibrium scores suggests clinicians and researchers allow one pracatice trial before recording test scores for baseline measurements.

The influence of dynamic visual cues for postural control in children aged 7–12 years

Young children rely heavily on vision for postural control during the transition to walking. Although by 10 years of age, children have automatic postural responses similar to adults, it is not clear when the integration of sensory inputs becomes fully developed. The purpose of this study was to examine this transition in the sensory integration process in children aged 7-12 years. Healthy children and adults stood on a fixed or sway-referenced support surface while viewing full-field optic flow scenes that moved sinusoidally (0.1 and 0.25 Hz) in an anterior-posterior direction. Center of pressure was recorded, and measures of sway amplitude and phase were calculated at each stimulus frequency. Children and adults had significant postural responses during approximately two-thirds of the trials. In adults, there was a 90% decrease in sway on the fixed surface compared with the sway-referenced surface, but only a 50% decrease in children. The phase between the optic flow stimulus and postural response in children led that of adults by 52 degrees at 0.1 Hz and by 15 degrees at 0.25 Hz. Adults and children aged 7-12 years have similar ability to use dynamic visual cues for postural control. However, 7-12-year-old children do not utilize somatosensory cues to stabilize posture to the same extent as adults when visual and somatosensory cues are conflicting.

Sensorimotor Dysfunction in HIV/AIDS: Effects of Antiretroviral Treatment and Comorbid Psychiatric Disorders

Balance and gait problems have repeatedly been mentioned in case descriptions of patients infected with Human Immunodeficiency Virus (HIV-1). Objective evidence of these problems has rarely been reported, however. Furthermore, the extent to which balance and gait are influenced by antiretroviral medications or comorbid psychiatric disorders has rarely been examined. The study compared 78 HIV-1 seronegative volunteers to 28 HIV/AIDS patients receiving no antiretroviral therapy, 25 patients receiving only nucleoside analogue therapy, and 37 patients receiving Highly Active Antiretroviral Therapy (HAART). The dependent measures included Equilibrium Quotient scores recorded during 3 subtests of the Sensory Organization Test (SOT), the number of falls during each subtest, the functional base of support, gait speed and cadence, single leg balance time, proximal strength, and vibrotactile threshold of the foot. The analysis employed the number of alcohol and drug abuse problems, depression severity, and body mass index as covariates. ANCOVAs revealed significant decrements in the 3 HIV-1 seropositive groups relative to the control group on Equilibrium Quotient scores during the most difficult of the SOT subtests (sway-referenced support surface with eyes-closed). HIV/AIDS patients also exhibited a smaller functional base of support and greater vibrotactile thresholds. Antiretroviral treatment did not affect balance; but, it did alter sensory threshold in a complex manner. HIV/AIDS is associated with reliable decrements in balance and peripheral sensory function which are variably sensitive to antiretroviral treatment. The implications of these findings for mobility, and workplace or operator safety, should be contemplated.

Postural control--a comparison between patients with chronic anterior cruciate ligament insufficiency and healthy individuals.

Postural control in the sagittal plane was evaluated in 22 patients with chronic anterior cruciate ligament (ACL) deficiency and the result was compared to that of a control group of 20 uninjured subjects. Measurement of the body sway was done on a fixed and sway-referenced force plate in both single-limb and two-limb stance, with the eyes open and closed, respectively. Further, an analysis of the postural reactions to perturbations backwards and forwards, respectively, was made in single-limb stance. The results demonstrated statistically significant deficits of the postural control in the patient group compared to the control group, but also within the patient group. There was a significantly higher body sway within the patient group when standing on a stable support surface on the injured limb than standing on the uninjured limb with the eyes open, but no difference with the eyes closed. When standing on a stable support surface, there was a significantly higher body sway in the patient group standing on the injured leg than in the control group, both with eyes open and closed. The patient group also showed a significantly impaired postural control compared to the control group when standing on the uninjured leg with the eyes closed. There was no difference between the groups in the two-limb stance. When standing on the sway-referenced support surface, the patient group had a significantly larger body sway than the control group when the eyes were open, but there was no significant difference between the groups with the eyes closed. The measurement of the postural corrective responses to perturbations backwards and forwards showed that the reaction time measured from the initiation of the force plate translation, and the amplitude of the body sway was significantly greater in the patient group than in the control group. We conclude that patients with a continuing chronic ACL insufficiency several years after injury have an impaired postural control in the antero-posterior direction in single-limb stance on their injured leg. They also show a greater body sway and a prolonged reaction time when subjected to antero-posterior perturbations when standing on their injured leg.