April J. Chambers

Gait parameters as predictors of slip severity in younger and older adults

This study investigated the association between slip severity and pre-slip gait characteristics of younger and older subjects. Sixteen younger and eleven older healthy adults walked onto an unexpectedly slippery surface. Slip severity was categorized as either hazardous or non-hazardous using a 1.0 ms peak slip velocity threshold. The results showed that hazardous slips were associated with greater step lengths (normalized by leg length) (SLR), larger and more rapidly changing foot – floor angles (FFA) at heel strike, and increased cadence across the two subject groups. Older subjects were found to walk with shorter SLR and with smaller and more slowly changing FFA at heel strike compared to younger subjects. However, both younger and older subjects experienced hazardous slips at the same rate. A logistic regression model relating SLR and cadence to slip severity predicted that increased SLR and decreased cadence would result in increased probability of hazardous slip (R2 = 0.45, χ2 = 15.30, p<0.01). A second logistic regression model relating FFA with slip severity predicted that increased FFA would result in increased probability of hazardous slip (R2 = 0.53, χ2 = 16.55, p<0.01). These results suggest that gait characteristics prior to foot contact play an important role in the severity of an ensuing slip. The finding that older adults experienced hazardous slips at the same rate as young adults even though their SLR and FFA are smaller suggests that age is also playing a role in other aspects of postural control that impact slip severity.

Dynamic postural stability during advancing pregnancy.

UNLABELLED Pregnant women are at an increased risk of experiencing a fall. Numerous anatomical, physiological, and hormonal alterations occur during pregnancy, but the influence of these factors on dynamic postural stability has not been explored. The purpose of this study was to examine dynamic postural stability in pregnant women during their second and third trimesters as well as in a group of non-pregnant control women. METHODS Eighty-one women (41 pregnant, 40 controls) participated stood on a force plate that translated anteroposteriorly at small, medium, and large magnitudes. Reaction time and center of pressure (COP) movement during the translations were analyzed. Trimester, perturbation direction, and perturbation magnitude were the independent variables in a mixed-model analysis of variance on each of the following dependent variables: reaction time, initial sway, total sway, and sway velocity. RESULTS Reaction time to the perturbation was not significantly different between the groups. Initial sway, total sway, and sway velocity were significantly less during the third trimester than during the second trimester and when compared to the non-pregnant controls (P<0.05). No differences were found in any of the measures between the pregnant women in their second trimesters and the control group. CONCLUSION Alterations in sway responses to perturbations are seen in the third trimester in healthy women with uncomplicated pregnancies. Further study is needed to examine the biomechanical and physiological reasons behind this altered dynamic postural stability.

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.

Dynamic postural stability in pregnant fallers and non-fallers

Please cite this paper as: McCrory J, Chambers A, Daftary A, Redfern M. Dynamic postural stability in pregnant fallers and non‐fallers. BJOG 2010;117:954–962.

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.

Fluid pressures at the shoe-floor-contaminant interface during slips: Effects of tread & 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.

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.

Comparison of microsuspension laryngoscopy positions: A randomized, prospective study

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.

Changes in Walking Characteristics of Young and Older Adults When Anticipating Slippery Floors

OCCUPATIONAL APPLICATIONS Differences in gait speed control strategies when anticipating a potentially slippery floor were found across age groups, with a group of mostly young adults adopting a potentially more risky strategy consisting of increased step length. Walking across a potentially slippery floor is common in the workplace, and warnings are one way to address this potential hazard. A better understanding of the influence of warnings about potentially slippery surfaces on gait could be used during slip training interventions and prevention programs to help reduce occupational slip-related falls. Specifically, these trainings/programs might benefit from addressing how to modulate gait speed through increased cadence rather than increased step length alone. Adults in both age groups tested here implemented potentially risky proactive strategies, highlighting the need to consider workers of all ages when designing occupational slip prevention measures. TECHNICAL ABSTRACT Background: Slips and falls are a major cause of occupational injury and costs. Certain proactive gait strategies can minimize fall risk. Purpose: This study investigated the impact of anticipating slippery floors on peak required coefficient of friction and spatiotemporal gait characteristics among young and older adults, including gait speed control, during walking on dry surfaces. Methods: Eighteen young (20–33 years) and 13 older participants (55–67 years) walked across a dry surface (baseline), experienced an unexpected slip, and walked across another dry surface with warning of a potentially slippery surface (anticipation). General spatiotemporal gait parameters and required coefficient of friction during walking were derived. Results: Young and older adults decreased required coefficient of friction and increased cadence during anticipation, both of which are important in reducing slip risk. Cluster analysis revealed three gait speed control strategies: Cluster 1 = mostly young adults who increased speed, cadence, and step length during anticipation; Cluster 2 = young and older adults who walked with minimal change in speed; Cluster 3 = only older adults who decreased speed through decreasing cadence and step length. Changes in cadence and step length were significantly correlated with changes in speed in older adults; only changes in step length were significantly correlated with changes in speed among young. Conclusions: Walking with decreased required coefficient of friction and increased cadence is beneficial when anticipating a slippery floor. However, walking with increased step length (Cluster 1) could increase slip risk. Avoiding gait speed modulations on potentially slippery surfaces through changes in step length alone should be addressed in occupational slip training and prevention. Interventions aimed at reducing slip risk should focus on increasing cadence if increases in gait speed are desired. Potentially risky proactive strategies implemented highlight the need to include workers of all ages in slip prevention training programs.

Shoe–Floor Frictional Requirements During Gait after Experiencing an Unexpected Slip

OCCUPATIONAL APPLICATIONS This study provides the first description of gait changes after a slip experience with no threat of additional slippery surfaces. The age-related differences found after experiencing an unexpected slip provide valuable information that should be considered when designing slip paradigms, slip-prevention measures, and the workplace. Specifically, the possibility of generating more than one unexpected slip would allow researchers to further investigate this unique event to prevent falls in the workplace. It is important to understand how frictional requirements and other gait adaptations are impacted by experiencing a slip to ensure that ergonomic interventions, such as shoe–floor design, slip-prevention training, and warning systems, can be effective. Safety warning systems should also be a focus of slip prevention in the workplace, since experiencing a slip alone may not have a long-lasting effect on gait adaptations that could minimize future slip risk, especially in young adults. TECHNICAL ABSTRACT Background: High injury rates and costs associated with occupational falls make them an important prevention target. Purpose: The goal of this study was to examine the impact of experiencing a slip on the peak required coefficient of friction during subsequent gait trials in which subjects were informed that the floor was no longer slippery. Methods: Twenty-seven young (20–31 years) and 25 older adults (50–65 years) walked across a dry floor (baseline dry) then experienced an unexpected slip. Following this, 15 dry trials (recovery dry) and a second unexpected slip were completed. Required coefficient of friction and general spatiotemporal gait parameters were derived during walking on dry surfaces. Results: Young adults initially reduced their peak required coefficient of friction on the left (previously slipped) foot but, after being informed that the floor was no longer slippery, eventually returned to within baseline levels of peak required coefficient of friction and walked with faster gait and longer steps. Young adults exhibited a second slip of similar magnitude to their first slip. Older adults continued walking more cautiously, with a decreased peak required coefficient of friction and other gait adaptations, after experiencing a slip, even though there was no threat of a subsequent slip. With this cautious gait, older adults experienced over a 40% decrease in peak slip velocity in the second slip event. Conclusions: The age-related differences found after experiencing an unexpected slip provide valuable information that should be considered when designing slip paradigms, slip-prevention measures, and the workplace. The possibility of generating more than one unexpected slip would allow researchers to further investigate this unique event to prevent falls in the workplace. It is important to understand how frictional requirements and other gait adaptations are impacted by experiencing a slip, to ensure that ergonomic interventions, such as shoe–floor design, slip-prevention training, and warning systems, can be effective. Safety warning systems should also be a focus of slip prevention in the workplace, since experiencing a slip alone may not have a long-lasting effect on gait adaptations that could minimize future slip risk, especially in young adults.