Algorithm Validation for Quantifying ActiGraph™ Physical Activity Metrics in Individuals with Chronic Low Back Pain and Healthy Controls.

Assessing physical activity is important in the treatment of chronic conditions, including chronic low back pain (cLBP). ActiGraph™, a widely used physical activity monitor, collects raw acceleration data, and processes these data through proprietary algorithms to produce physical activity measures. The purpose of this study was to replicate ActiGraph™ algorithms in MATLAB and test the validity of this method with both healthy controls and participants with cLBP. MATLAB code was developed to replicate ActiGraph™'s activity counts and step counts algorithms, to sum the activity counts into counts per minute (CPM), and categorize each minute into activity intensity cut points. A free-living validation was performed where 24 individuals, 12 cLBP and 12 healthy, wore an ActiGraph™ GT9X on their non-dominant hip for up to seven days. The raw acceleration data were processed in both ActiLife™ (v6), ActiGraph™'s data analysis software platform, and through MATLAB (2022a). Percent errors between methods for all 24 participants, as well as separated by cLBP and healthy, were all less than 2%. ActiGraph™ algorithms were replicated and validated for both populations, based on minimal error differences between ActiLife™ and MATLAB, allowing researchers to analyze data from any accelerometer in a manner comparable to ActiLife™.

Obesity-Specific Considerations for Assessing Gait with Inertial Measurement Unit-Based vs. Optokinetic Motion Capture.

Adults with obesity experience high rates of disability and rapid functional decline. Identifying movement dysfunction early can direct intervention and disrupt disability development; however, subtle changes in movement are difficult to detect with the naked eye. This study evaluated how a portable, inertial measurement unit (IMU)-based motion capture system compares to a laboratory-based optokinetic motion capture (OMC) system for evaluating gait kinematics in adults with obesity. Ten adults with obesity performed overground walking while equipped with the OMC and IMU systems. Fifteen gait cycles for each participant were extracted for the 150 total cycles analyzed. Kinematics were compared between OMC and IMU across the gait cycles (coefficient of multiple correlations), at clinically significant time points (interclass correlations), and over clinically relevant ranges (Bland-Altman plots). Sagittal plane kinematics were most similar between systems, especially at the knee. Sagittal plane joint angles at clinically meaningful timepoints were poorly associated except for ankle dorsiflexion at heel strike (ρ = 0.38) and minimum angle (ρ = 0.83). All motions except for ankle dorsiflexion and hip abduction had >5° difference between systems across the range of angles measured. While IMU-based motion capture shows promise for detecting subtle gait changes in adults with obesity, more work is needed before this method can replace traditional OMC. Future work should explore standardization procedures to improve consistency of IMU motion capture performance.

Weekly minutes of moderate to vigorous physical activity is associated with movement quality in overweight and obese older adults, independent of age.

BACKGROUND: Physical activity can improve function and decrease healthcare spending among overweight and obese older adults. Although unstructured physical activity has been related to cardiometabolic improvements, the relationship between unstructured activity and movement quality is unclear. AIMS: This study aimed to evaluate the association of amount of unstructured free-living moderate-vigorous physical activity (MVPA) with measures of movement quality in overweight and obese older adults. METHODS: The association of MVPA with movement quality was assessed in 165 overweight and obese older adults (Age: 77.0(8.0) years; Body mass index (BMI): 29.2(5.3) kg/m2). Participants performed overground walking, the Figure of 8 Walk test, and the Five-Times Sit to Stand. Weekly physical activity was measured using a waist-worn Actigraph activity monitor. RESULTS: Movement quality during straight path [gait speed (ρ = 0.30, p < 0.01), stride length (ρ = 0.33, p < 0.01), double-limb support time (ρ = -0.26, p < 0.01), and gait symmetry (ρ = 0.17, p = 0.02)] and curved path [F8W time (ρ = -0.22, p < 0.01) and steps (ρ = -0.22, p < 0.01)] walking were associated with weekly minutes of MVPA after controlling for age. Five-Times Sit to Stand performance was not significantly associated with weekly minutes of MVPA (ρ = -0.10, p = 0.13). CONCLUSIONS: Older adults with high BMIs who are less active also demonstrate poorer movement quality, independent of age. Physical activity engagement and task-specific training should be targeted in interventions to promote healthy aging, decrease falls, and delay disability development. Future work should consider the interconnected nature of movement quality with physical activity engagement and investigate if targeting one influences the other.

Weekly minutes of moderate to vigorous physical activity is associated with movement quality in overweight and obese older adults.

Background: Physical activity can improve function and decrease healthcare spending among overweight and obese older adults. Although unstructured physical activity has been related to cardiometabolic improvements, the relationship between unstructured activity and movement quality is unclear. Aims: This study aimed to evaluate the association of amount of unstructured free-living moderate-vigorous physical activity (MVPA) with measures of movement quality in overweight and obese older adults. Methods: The association of MVPA with movement quality was assessed in 165 overweight and obese older adults (Age: 77.0(8.0) years; Body mass index (BMI): 29.2(5.3) kg/m2). Participants performed overground walking, the Figure of 8 Walk test, and the Five-Times Sit to Stand. Weekly physical activity was measured using a waist-worn Actigraph activity monitor. Results: Movement quality during straight path (gait speed (ρ = 0.30, p < 0.01), stride length (ρ = 0.33, p < 0.01), double-limb support time (ρ=-0.26, p < 0.01), and gait symmetry (ρ = 0.17, p = 0.02)) and curved path (F8W time (ρ=-0.22, p < 0.01) and steps (ρ=-0.22, p < 0.01)) walking were associated with weekly minutes of MVPA after controlling for age. Five-Times Sit to Stand performance was not significantly associated with weekly minutes of MVPA (ρ=-0.10, p = 0.13). Conclusions: Older adults with high BMIs who are less active also demonstrate poorer movement quality which should be targeted in interventions to promote healthy aging, decrease falls, and delay disability development. Future work should explore if these associations are observed in middle-aged adults so targeted interventions can be implemented even earlier in the disability development continuum.

Inertial measurement unit-based motion capture to replace camera-based systems for assessing gait in healthy young adults: Proceed with caution.

Gait analysis can identify injury-risk markers indiscernible to the naked eye. Inertial measurement unit (IMU)-based motion capture circumvents optokinetic motion capture (OMC) clinical implementation barriers with its portability, increased affordability, and decreased computational burden. We compared an IMU system to a robust OMC marker set for gait analysis. 10 healthy adults walked at self-selected speeds equipped with Noraxon MyoMotion IMUs and a 24-marker, 5-cluster marker-set in view of 14 OMC cameras. A single calibration was applied. IMU system and OMC calculated joint angles were compared. A single calibration performed similarly to previously reported repeated calibration. IMU and OMC agreement was best in the sagittal plane with IMU axis-mixing affecting off-sagittal plane agreement. System differences were greater than 5° for most motions. Measurement system bias showed at the ankle and knee, however differences varied across participants. IMU kinematics should be interpreted with caution; consistency and accuracy must improve before IMUs can replace OMC.

Reducing Slip Risk: A Feasibility Study of Gait Training with Semi-Real-Time Feedback of Foot-Floor Contact Angle.

Slip-induced falls, responsible for approximately 40% of falls, can lead to severe injuries and in extreme cases, death. A large foot-floor contact angle (FFCA) during the heel-strike event has been associated with an increased risk of slip-induced falls. The goals of this feasibility study were to design and assess a method for detecting FFCA and providing cues to the user to generate a compensatory FFCA response during a future heel-strike event. The long-term goal of this research is to train gait in order to minimize the likelihood of a slip event due to a large FFCA. An inertial measurement unit (IMU) was used to estimate FFCA, and a speaker provided auditory semi-real-time feedback when the FFCA was outside of a 10-20 degree target range following a heel-strike event. In addition to training with the FFCA feedback during a 10-min treadmill training period, the healthy young participants completed pre- and post-training overground walking trials. Results showed that training with FFCA feedback increased FFCA events within the target range by 16% for "high-risk" walkers (i.e., participants that walked with more than 75% of their FFCAs outside the target range) both during feedback treadmill trials and post-training overground trials without feedback, supporting the feasibility of training FFCA using a semi-real-time FFCA feedback system.

Development and validation of body fat prediction models in American adults.

INTRODUCTION: Commonly used statistical models to predict body fat percentage currently rely on skinfold measures, anthropometric measures, or some combination of the two but do not account for the wide ranges of age and body mass index (BMI) present in the American adult population. The objective of this study was to develop a statistical regression model to predict in vivo body fat percentage (dual energy X-ray) in men and women across significant age and obesity ranges. METHODS: This study included 228 adults between the ages of 21 and 70, with BMI between 18.5 and 40.0 kg m-2. The study population was split into training (n = 163) and validation (n = 65) groups, which were used to develop and validate the prediction models. The models were developed on the training group using a backwards stepwise regression analysis, with the initial predictors including age, BMI, and several anthropometric and skinfold measurements. RESULTS: The final statistical regression models included age, BMI, anthropometric measures, and skinfold measures with significant effects following the stepwise process. The models predicted body fat percentage in the testing group with average errors of less than 0.10% body fat in males and females, while the four previously existing methods (Durnin, Hodgdon, Jackson, and Woolcott) significantly underestimated or overestimated body fat in both genders, with errors ranging between 2% and 10%. CONCLUSIONS: The final models included hand thickness, and the female model was dependent on waist circumference and two of the skinfold measures, while the male model used hip and thigh circumferences, along with three skinfold measures. By including the skinfold measurements separately, instead of only as sums like previous models have done, these models can account for the different relative contributions of each site to total body fat.

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 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.

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.

Age and body mass index associations with body segment parameters.

Body segment parameters (BSPs) such as segment mass, center of mass, and radius of gyration are required in many ergonomic tools and biomechanical models to estimate injury risk, and quantify muscle and joint contact forces. Currently, the full effects of age and obesity have not been taken into account when predicting BSPs. The goal of this study is to quantify the impact of body mass index (BMI) and age on BSPs, in order to provide more representative measures necessary for modeling inputs. A whole body dual energy X-ray absorptiometry (DXA) scan was collected for 280 working men and women with a wide range of BMI and aged 21 to 70 years. Established DXA processing methods were used to determine in-vivo estimates of the mass, center of mass, and radius of gyration for the upper arm, forearm, torso, thigh, and shank for males and females. Regression models were used to determine if age and BMI terms, as well as their interactions, were associated with these BSPs. The variability in BSPs explained by BMI alone ranged from 4 to 51%, and age explained an additional 3-19%. Thus, BMI and age are significant correlates of BSPs, and need to be taken into account when predicting certain BSPs in order to obtain accurate and representative results in biomechanical models.

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.

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.

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.

Effect of Trunk Segment Boundary Definitions on Frontal Plane Segment Inertial Calculations.

When defining trunk body segment parameters, such as segment length, mass, center of mass location, and radius of gyration, it is necessary to understand and define consistent, anatomically relevant segment boundaries. In addition to the differences in reported trunk parameters due to different data collection and analysis methods (such as cadaver studies and imaging methods), many previous publications have also used differing definitions of the trunk segment. The objective of this study was to determine the effect of differences in trunk segment definitions and obesity on the calculated mass, center of mass, and radius of gyration using dual-energy X-ray absorptiometry anthropometry calculations. Twenty-three participants were recruited in normal weight and morbidly obese body mass index categories. A frontal plane dual-energy X-ray absorptiometry scan was taken of each participant, and 3 trunk segment delineations used by Chambers, de Leva, and Zatsiorsky were used to calculate the trunk parameters. The results showed statistically significant effects of segmentation definition and obesity on the trunk parameters calculated. Because of the potential impacts on static modeling and inverse dynamics calculations, it is important to determine which trunk segmentations are most appropriate for specific applications and to account for the impact of obesity within individuals.

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.

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.

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.

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.