Inhibition and decision-processing speed are associated with performance on dynamic posturography in older adults.

Changes in cognition due to age have been associated with falls and reduced standing postural control. Sensory integration is one component of postural control that may be influenced by certain aspects of cognitive functioning. This study investigated associations between measures of cognitive function and sensory integration capabilities for healthy young and older adults. Dynamic posturography was performed using the Equitest Sensory Organization Test (SOT) protocol to evaluate sensory integration during standing using sway-referencing of the platform and/or visual scene to alter somatosensory and visual inputs. The Equilibrium Score was used as a measure of sway. Cognitive testing examined aspects of cognitive function that have been associated with falls in older adults. A correlational analysis investigated associations between the cognitive measures and postural sway during the altered sensory conditions of the SOT. For older subjects only, slower decision-processing speed was associated with increased sway during SOT conditions whenever somatosensation was altered. Reduced perceptual inhibition was associated with increased sway whenever somatosensation was intact, and particularly when vision was altered in the presence of somatosensation. Visuospatial construct ability was associated with sway only when the eyes were closed during altered somatosensation. Task-switching was associated with sway only when vision and somatosensation were intact. With increased age, deficits in decision speed and inhibition appear associated with the sensory integration crucial for balance maintenance. Associations are modulated by the availability of somatosensation and vision. These associations define situations and individual differences in aspects of cognition that may relate to situational loss of balance in older adults.

The Effect of Prolonged Walking With Intermittent Standing on Erector Spinae and Soleus Muscle Oxygenation and Discomfort.

Prolonged periods of walking have been associated with musculoskeletal discomfort and injuries. Previous research has shown that muscle fatigue is related to decreases in muscle oxygenation during short term walking. The objective of the proposed research is to determine the impact of prolonged walking with intermittent standing on musculoskeletal discomfort and muscle oxygenation measures in young adults. Nine young adults walked for a period of 2 hours. Ratings of perceived discomfort were recorded using a questionnaire. Muscle oxygenation and hemoglobin levels were collected from the lower back erector spinae and soleus muscles using near infrared spectroscopy (NIRS). Subjective discomfort significantly increased throughout the 2 hours. Prolonged walking generally induced increased oxygenation of the erector spinae and soleus across walking periods, within walking periods and across standing periods. These increases were more pronounced at the beginning of the walking session and continued through the second or third periods. Erector spinae and soleus total hemoglobin increased within walking period one and two. Only the soleus total hemoglobin significantly increased after the first walking and standing periods and during all the transitions from walking to standing. Increased oxygenation and total hemoglobin during prolonged walking with intermittent standing are likely a result of the repeated dynamic contractions and exercise-induced blood volume expansion. Increased discomfort was found; however, this was not explained by detrimental changes in oxygenation or total hemoglobin.

Perceptual Inhibition Associated with Sensory Integration for Balance in Older Adults.

AIMS: Inhibition associated with perception has been implicated in sensory integration processes for balance when sensory conflict occurs. The current study examines the associations of three measures of inhibition (perceptual inhibition, motor inhibition, and Stroop interference) with standing balance under sensory conflict conditions in younger and older adults. METHODS: Perceptual inhibition, motor inhibition, and Stroop interference were measured in younger and older subjects. Standing balance under conditions of sensory conflict was evaluated using a modified dynamic posturography protocol. Correlative analysis was performed to examine the associations between the inhibition measures and sway. RESULTS: In older adults only, perceptual inhibition was correlated with sway when sensory conflict was present. Stroop interference and motor inhibition were not significantly correlated with sway under any posturography conditions. CONCLUSION: Measures of perceptual inhibition are associated with reduced sensory integration capability for balance during sensory conflict conditions in older adults.

Sensory and motoric influences on attention dynamics during standing balance recovery in young and older adults.

This study investigated the impact of attention on the sensory and motor actions during postural recovery from underfoot perturbations in young and older adults. A dual-task paradigm was used involving disjunctive and choice reaction time (RT) tasks to auditory and visual stimuli at different delays from the onset of two types of platform perturbations (rotations and translations). The RTs were increased prior to the perturbation (preparation phase) and during the immediate recovery response (response initiation) in young and older adults, but this interference dissipated rapidly after the perturbation response was initiated (<220 ms). The sensory modality of the RT task impacted the results with interference being greater for the auditory task compared to the visual task. As motor complexity of the RT task increased (disjunctive versus choice) there was greater interference from the perturbation. Finally, increasing the complexity of the postural perturbation by mixing the rotational and translational perturbations together increased interference for the auditory RT tasks, but did not affect the visual RT responses. These results suggest that sensory and motoric components of postural control are under the influence of different dynamic attentional processes.

Torso kinematics during gait and trunk anthropometry in pregnant fallers and non-fallers.

BACKGROUND: Pregnant women experience numerous physiological and biomechanical alterations which may be associated with their increased risk of experiencing a fall. Gait alterations in other populations who fall include increased step width and mediolateral trunk motion. It is not known if pregnant women who have fallen exhibit these alterations. RESEARCH QUESTION: Our purpose was to examine torso kinematics and step width during gait in pregnant fallers, pregnant non-fallers and non-pregnant controls. We also examined trunk anthropometry in the pregnant groups to determine if pregnant fallers have different trunk physiques than pregnant non-fallers. METHODS: 3D kinematic data were collected on 14 pregnant fallers, 15 pregnant non-fallers and 40 non-pregnant controls. Pregnant women were in their second or third trimester of pregnancy. Frontal plane translations of C7 and L4, step width, stride length, walking velocity, and 3D thoracic and pelvic kinematics were determined. Anthropometric torso measurements were obtained on the pregnant women. A series of MANCOVAs was performed (covariate: walking velocity, α = 0.05) to compare the dependent variables between pregnant fallers, pregnant non-fallers, and controls. Tukey post-hoc analyses were performed when appropriate (α = 0.05). A MANOVA compared anthropometric variables between pregnant fallers and non-fallers (α = 0.05). RESULTS: Pregnant non-fallers exhibited greater step width and frontal and transverse plane angles at heel contact and range of motion over the gait cycle when compared to the fallers. Trunk anthropometry did not differ between pregnant fallers and non-fallers. SIGNIFICANCE: Pregnancy-associated gait alterations differed between fallers and non-fallers. Greater step width of the pregnant non-fallers increased the base of support, thus increasing stability. Exercise participation may allow pregnant women to better adapt to their altered physiques and be more able to prevent a fall should a trip or slip occur.

The effect of sit-stand desks on office worker behavioral and health outcomes: A scoping review.

This scoping review examines the effects of sit-stand desks (SSDs) on six domains: behavior (e.g. time sitting and standing), physiological, work performance, psychological, discomfort, and posture. Fifty-three articles met criteria. We determined the percentage of significant results for each domain. Forty-seven studies were experimental trials. Sample sizes ranged from six to 231 participants. Follow-up time-frames ranged from one day to one year. Sixty-one percent of behavioral (24 studies), 37% of physiological (28 studies), 7% of work performance (23 studies), 31% of psychological (11 studies), 43% of discomfort (22 studies), and 18% of posture domain results (4 studies) were significant. We conclude that SSDs effectively change behaviors, but these changes only mildly effect health outcomes. SSDs seem most effective for discomfort and least for productivity. Further study is needed to examine long-term effects, and to determine clinically appropriate dosage and workstation setup.

A Novel Method of Analysis for Prolonged-Standing Data: Accounting for Joint and Muscle Discomfort.

Background: The typical American worker spends about two-thirds of their work day standing. Prolonged standing has been found to be associated with acute and chronic adverse health outcomes. There is considerable variability among existing methods of analysis for prolonged-standing data, and therefore difficulty interpreting and comparing results across studies. Purpose: The purpose of this study is to develop a bodyweight transfer analysis method that incorporates factors of both time and amplitude of loading. This method was then applied to actual prolonged-standing data, to understand how the results of this method are impacted by time spent standing, and how the results relate to previously-reported methods of analysis for weight shifting data. Methods: Seven subjects (six male, one female) stood with each foot on one of two force plates for 6 h with a 5-min seated rest break between hours. Our new method identified two different types of events: fidgets and weight shifts. Center-of-pressure data were analyzed with the proposed method and three existing methods of analysis. Results: Subjects utilized different quantities of fidgets and weight shifts over the course of the trials. Existing methods of analysis identified a wide range in number of events, with some methods consistently identifying more events than others. These existing methods significantly differed from the proposed method. Fidgets, weight shifts, and fidgets + weight shifts, as identified using the proposed method, had significant interactions with time, while only one of the existing methods showed a significant time interaction. Conclusions: The conclusions drawn from analysis of prolonged standing center-of-pressure data can differ significantly depending on the method of analysis used. The method proposed here accounts for the different sources of discomfort and the tissue characteristics of these sources. Future work should explore the relationships between physiologic parameters and fidgets and weight shifts, so that appropriate clinical interventions can be identified.

Slip-related muscle activation patterns in the stance leg during walking.

Falls precipitated by slipping are a serious public health concern especially in the elderly. Muscular responses generated during slipping have not been investigated during gait on contaminated floors. This study compared slip-related muscular responses (reactive and proactive) in young and older adults and examined if characteristics of muscular activation patterns during normal gait impact slip severity on contaminated floors. Electromyographic recordings were made from the major shank and thigh muscles in the stance leg of 11 young and nine older adults. Three experimental conditions were included: (1) known dry floors (baseline), (2) unexpected contaminated floor, (3) alert dry (subjects uncertain of the floor's contaminant condition). Muscular responses to unexpected slips, similar in both age groups, included the activation of the Medial Hamstring (approximately 175 ms) followed by the onset of the Vastus Lateralis (approximately 240 ms). The power and duration of responses were scaled to slip severity. The Vastus Lateralis latency was delayed in severe slips. When experiencing a severe slip, young adults demonstrated a longer, more powerful response compared to older adults. Subjects who normally walk with greater ankle muscle co-contraction were predisposed to experience less severe slips when encountering an unexpected slippery floor. Finally, anticipation of a slippery surface resulted in more powerful muscular activity and muscle co-contraction at the ankle and knee compared to baseline gait, as well as earlier onsets and longer durations in the posterior muscles' activation. These findings may provide a greater understanding of the higher incidence of falls in the elderly.

Arm reactions in response to an unexpected slip-Impact of aging.

Slips and falls represent a serious public safety concern in older adults, with the segment of the United States population over the age of 65 accounting for about three quarters of all fall related deaths. The majority of falls in older adults are due to trips and slips. The objective of this study was to investigate how age affects arm reactions generated in response to unexpected slips. Thirty-three participants divided into two age groups (16 young, 17 old) participated in this study. Participants were exposed to two conditions: known dry walking (baseline) and an unexpected slip initiated when stepping onto a glycerol-contaminated floor. The upper extremity parameters of interest included the timing and amplitude of the shoulder flexion moment generated in response to the slip as well as the resulting angular kinematics (trajectories). The analysis of the kinetic data revealed a delayed shoulder flexion reaction to slips in older adults compared to their young counterparts, as well as a greater flexion moment magnitude. Knowledge of such upper body reaction mechanisms to unexpected slips may help to improve balance recovery training in older adults, as well as aid in the implementation of environmental modifications, e.g. handrails, to reduce falls-related injuries.

Comparison of microsuspension laryngoscopy positions: a randomized, prospective study.

OBJECTIVES/HYPOTHESIS: To evaluate muscle fatigue and participant pain in the upper back, cervical, and arm muscles associated with microlaryngeal surgery (MLS) in standardized favorable and unfavorable ergonomic positions. STUDY DESIGN: Individual randomized counterbalanced design. METHODS: Electromyographic sensors were placed on targeted muscles involved with performing MLS on 18 otolaryngology residents/fellows. Subjects were randomly counterbalanced in both favorable and unfavorable positions while completing simulated laryngeal microsurgical tasks. Participants reported their extent of muscle discomfort in targeted muscle regions on a standardized survey. RESULTS: Muscle fatigue and self-reported pain were reduced, and productivity was improved in the favorable position. In the lower trapezius, significantly less muscle activation (P = 0.025) and less pain (P < 0.05) were found while in the favorable position compared to the unfavorable position. CONCLUSION: This is the first study to demonstrate electromyographic evidence of decreased muscle activation and fatigue, in addition to self-reported pain with a more favorable microsurgical ergonomic position, which may help surgeons avoid musculoskeletal injuries.

Ground reaction forces during stair locomotion in pregnant fallers and non-fallers.

BACKGROUND: More than 27% of pregnant women fall. Approximately 40% of falls occur during staircase locomotion. The purpose of this study was to examine ground reaction forces in pregnant fallers, pregnant non-fallers, and non-pregnant controls to determine if pregnant fallers display alterations to ground reaction forces that increase their risk of falling on stairs. METHODS: Fifteen pregnant fallers and 14 pregnant non-fallers participated during their second and third trimesters. Forty non-pregnant women served as controls. Subjects ascended and descended a four-step staircase. A force plate in the second stair collected ground reaction forces. Ascent and descent velocities were assessed. In the statistics, group (pregnant faller, pregnant non-faller, control) and subject were independent variables. Stance time and ascent/descent velocity were analyzed with an ANOVA. Mediolateral center of pressure excursion was analyzed with an analysis of covariance. Ground reaction forces were categorized into anterioposterior, mediolateral, and vertical forces and normalized to the subject's bodyweight. A multivariate analysis of covariance was used to compare between groups and subjects for each force category, with velocity as the covariate (α = 0.05). FINDINGS: Pregnant fallers had an increased anterioposterior braking impulse (P < 0.01), medial impulse (P = 0.02), and minimum between vertical peaks (P = <0.01) during ascent. During descent, pregnant fallers demonstrated a smaller anterioposterior propulsive peak and propulsive impulse (P = 0.03) and a greater minimum between vertical peaks (P<0.01). INTERPRETATION: These alterations are likely related to a strategy used by pregnant fallers to increase stability during staircase locomotion.

The pregnant "waddle": an evaluation of torso kinematics in pregnancy.

UNLABELLED: Although pregnant women are anecdotally said to "waddle" during gait, researchers have not quantified the kinematics of these gait alterations. The purpose of this study was to examine the effects of pregnancy on thoracic and pelvic kinematics during gait. METHODS: Data were collected on 29 pregnant subjects in the mid-second and third trimesters and on 40 control women. Three-dimensional kinematic data were collected on subjects walking at their freely-chosen speed. Right foot heel-strike (RHS) and left foot toe-off (LTO) were determined from force plate data. Thoracic and pelvic angles at RHS, step width, mediolateral translation of the C7 and L4 vertebrae, and the ranges of motion (ROMs) of the thorax and pelvis over the gait stride were determined. A series of MANCOVAs were performed with trimester (second, third, and control) as the independent variable and velocity as the covariate (α=0.05). Post-hoc analyses were performed when appropriate. RESULTS: Increased lateral translation of the C7 and L4 vertebrae (third trimester>second trimester>control, p<0.05) was noted, accompanied by an increased step width in the third trimester (p=0.03). At heel strike, pregnant women had greater thoracic extension (third trimester>second trimester>control, p<0.05) and greater anterior pelvic tilt (third trimester>control; p<0.05). Sagittal plane thoracic ROM was less in the third trimester compared to controls (p<0.01). CONCLUSIONS: Pregnant women demonstrated a lateral shifting of the body during gait, which accompanied a greater step width. The increased thoracic extension and anterior pelvic tilt, along with decreased sagittal plane ROM are likely adaptations to increased abdominal size.

Fluid pressures at the shoe-floor-contaminant interface during slips: effects of tread and implications on slip severity.

Previous research on slip and fall accidents has suggested that pressurized fluid between the shoe and floor is responsible for initiating slips yet this effect has not been verified experimentally. This study aimed to (1) measure hydrodynamic pressures during slipping for treaded and untreaded conditions; (2) determine the effects of fluid pressure on slip severity; and (3) quantify how fluid pressures vary with instantaneous resultant slipping speed, position on the shoe surface, and throughout the progression of the slip. Eighteen subjects walked on known dry and unexpected slippery floors, while wearing treaded and untreaded shoes. Fluid pressure sensors, embedded in the floor, recorded hydrodynamic pressures during slipping. The maximum fluid pressures (mean+/-standard deviation) were significantly higher for the untreaded conditions (124+/-75 kPa) than the treaded conditions (1.1+/-0.29 kPa). Maximum fluid pressures were positively correlated with peak slipping speed (r=0.87), suggesting that higher fluid pressures, which are associated with untreaded conditions, resulted in more severe slips. Instantaneous resultant slipping speed and position of sensor relative to the shoe sole and walking direction explained 41% of the fluid pressure variability. Fluid pressures were primarily observed for untreaded conditions. This study confirms that fluid pressures are relevant to slipping events, consistent with fluid dynamics theory (i.e. the Reynolds equation), and can be modified with shoe tread design. The results suggest that the occurrence and severity of unexpected slips can be reduced by designing shoes/floors that reduce underfoot fluid pressures.

Intra-individual variability in gait and in cognitive performance are not related in the elderly.

As humans age, the amount of intra-individual variability (IIV) present in both their gait and their cognitive performance tends to increase. Both gait and cognitive IIV are associated with attentional control and with cerebrovascular disease, suggesting that the IIV in gait and cognitive function should be strongly correlated in the elderly. In this study temporal gait variability was determined from a 60-second period of walking. Cognitive variability was determined from two decision-time tasks assessing inhibition. Despite the presence of substantial amounts of gait and cognitive IIV in 71 elderly individuals, there were no significant correlations between measures of cognitive and gait IIV, suggesting that different factors drive IIV in the motor and cognitive performance of older individuals. These results are not consistent with the common cause theory of aging, which predicts that cognitive and sensorimotor performance should show related declines due to age-related disruption of a common neurological substrate.

Ground reaction forces during stair locomotion in pregnancy.

UNLABELLED: Pregnant women experience numerous physical alterations during pregnancy which may place them at an increased risk of falls. The purpose of this study was to examine ground reaction forces (GRFs) during staircase locomotion in pregnant and non-pregnant women. METHODS: Data were collected on 29 pregnant women in their second and third trimesters, and on 40 control women. Subjects walked at their freely chosen speeds during stair ascent and descent. A force plate imbedded in the second stair, but structurally independent of the staircase, was used to collect GRF data (1080 Hz). A marker placed on the L3/L4 spinal segment was used to determine ascent and descent velocity from a motion-capture system. In the statistical analyses, trimester (control, second trimester, third trimester) and subject were the independent variables. Stance time and ascent/descent velocity were analyzed with an ANOVA. Mediolateral excursion of the COP during the step was analyzed with an ANCOVA. The GRFs were categorized into anterioposterior, mediolateral, and vertical forces. A two factor MANCOVA (subject, trimester) was performed on each GRF category. Mass and velocity served as covariates in each analysis (α=0.05). RESULTS: The mediolateral excursion of the COP during ascent was greater in the third trimester (p=0.04). The anterioposterior braking impulse was greater in both ascent (p=0.01) and descent (p=0.01) during pregnancy. The vertical GRF loading rate during descent was greater in pregnant women than in controls (p=0.04). CONCLUSION: These alterations are likely related to increased instability during stairway walking and could contribute to increased fall risk during pregnancy.

Differences in geriatric anthropometric data between DXA-based subject-specific estimates and non-age-specific traditional regression models.

Age, obesity, and gender can have a significant impact on the anthropometrics of adults aged 65 and older. The aim of this study was to investigate differences in body segment parameters derived using two methods: (1) a dual-energy x-ray absorptiometry (DXA) subject-specific method (Chambers et al., 2010) and (2) traditional regression models (de Leva, 1996). The impact of aging, gender, and obesity on the potential differences between these methods was examined. Eighty-three healthy older adults were recruited for participation. Participants underwent a whole-body DXA scan (Hologic QDR 1000/W). Mass, length, center of mass, and radius of gyration were determined for each segment. In addition, traditional regressions were used to estimate these parameters (de Leva, 1996). A mixed linear regression model was performed (α = 0.05). Method type was significant in every variable of interest except forearm segment mass. The obesity and gender differences that we observed translate into differences associated with using traditional regressions to predict anthropometric variables in an aging population. Our data point to a need to consider age, obesity, and gender when utilizing anthropometric data sets and to develop regression models that accurately predict body segment parameters in the geriatric population, considering gender and obesity.

Ground reaction forces during gait in pregnant fallers and non-fallers.

UNLABELLED: Pregnant women are at a high risk of experiencing a fall. To our knowledge, ground reaction forces (GRFs) in pregnant fallers and non-fallers have not been reported. PURPOSE: The purpose of this study was to examine the effects of pregnancy and fall history on GRFs during walking. METHODS: Forty one pregnant subjects in the mid 2nd and 3rd trimesters (pregnant fallers: n=15, pregnant non-fallers: n=14), and 40 control women walked at a freely chosen walking speed along an 8m walkway. A force plate, hidden in the walkway, was used to collect GRFs (1080Hz). Kinematic data (120Hz) were collected from a marker placed on the lumbar spine to estimate walking velocity. GRF variables included mediolateral Center of Pressure (COP) excursion, and GRFs normalized to body mass. A two factor ANOVA (trimester x fall group) was used to compare subject demographics, and walking velocity (α=0.05). A two factor ANCOVA (trimester×fall group, covariate: velocity) was performed to examine other GRF variables (Bonferroni corrected α=0.006) and the mediolateral COP excursion (α=0.05). RESULTS: Walking velocity was greater in the control group (p<0.05). No differences were seen in the GRFs or COP movement between trimesters or between pregnant fallers and non-fallers. CONCLUSIONS: When walking velocity was considered in the statistical model, ground reaction forces are essentially unchanged by pregnancy.

The effect of obesity and gender on body segment parameters in older adults.

BACKGROUND: Anthropometry is a necessary aspect of aging-related research, especially in biomechanics and injury prevention. Little information is available on inertial parameters in the geriatric population that account for gender and obesity effects. The goal of this study was to report body segment parameters in adults aged 65 years and older, and to investigate the impact of aging, gender and obesity. METHODS: Eighty-three healthy old (65-75 years) and elderly (>75 years) adults were recruited to represent a range of body types. Participants underwent a whole body dual energy X-ray absorptiometry scan. Analysis was limited to segment mass, length, longitudinal center of mass position, and frontal plane radius of gyration. A mixed-linear regression model was performed using gender, obesity, age group and two-way and three-way interactions (alpha=0.05). FINDINGS: Mass distribution varied with obesity and gender. Males had greater trunk and upper extremity mass while females had a higher lower extremity mass. In general, obese elderly adults had significantly greater trunk segment mass with less thigh and shank segment mass than all others. Gender and obesity effects were found in center of mass and radius of gyration. Non-obese individuals possessed a more distal thigh and shank center of mass than obese. Interestingly, females had more distal trunk center of mass than males. INTERPRETATION: Age, obesity and gender have a significant impact on segment mass, center of mass and radius of gyration in old and elderly adults. This study underlines the need to consider age, obesity and gender when utilizing anthropometric data sets.

Knee strength capabilities and slip severity.

Slips and falls are a serious public health concern in older populations. Reduced muscle strength is associated with increased age and fall incidence. Understanding the relationships between specific joint muscle strength characteristics and propensity to slip is important to identify biomechanical factors responsible for slip-initiated falls and to improve slip/fall prevention programs. Knee corrective moments generated during slipping assist in balance recovery. Therefore, the study goal was to investigate the relationship between knee flexion/extension strength and slip severity. Isometric knee flexion/extension peak torque and rate of torque development (RTD) of the slipping leg were measured in 29 young and 28 older healthy subjects. Motion data were collected for an unexpected slip during self-paced walking. Peak slip velocity (PSV) of the slipping heel served as a slip severity measure. Within-sex and age group regressions relating gait speed-controlled PSV to strength of the slipping leg revealed significant inverse PSV-knee extension peak torque and PSV-knee flexion/extension RTD relationships in young males only. Differences in PSV-strength relationships between sex and age groups may be caused by greater ranges of strength capabilities in young males. In conclusion, the ability to generate higher, more rapid knee flexion/ extension muscle moments (greater peak torque/RTD) may assist in recovery from severe slips.