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Background: Backward falls are often associated with injury, particularly among older women. An age-related increase occurs in center of pressure variability when standing and leaning. So, we hypothesized that, in comparison to young women, older women would display a disproportionate decrease of speed and accuracy in the primary center of pressure submovements as movement amplitude increases., Methods: Ground reaction forces were recorded from thirteen healthy young and twelve older women while performing rapid, targeted, center of pressure movements of small and large amplitude in upright stance. Measures included center of pressure speed, the number of center of pressure submovements, and the incidence rate of primary center of pressure submovements undershooting the target., Findings: In comparison to young women, older women used slower primary submovements, particularly as movement amplitude increased (P<0.01). Even though older women achieved similar endpoint accuracy, they demonstrated a 2 to 5-fold increase in the incidence of primary submovement undershooting for large-amplitude movements (P<0.01). Overall, posterior center of pressure movements of older women were 41% slower and exhibited 43% more secondary submovements than in young women (P<0.01)., Interpretations: We conclude that the increased primary submovement undershoots and secondary center of pressure submovements in the older women reflect the use of a conservative control strategy near the posterior limit of their base of support., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Objective: The primary goal of this study was to test the hypothesis that wearing the 3.7 kg vest portion of a radiological shielding garment (a "lead") significantly increases lower back and shoulder muscle activity in quasistatic erect and forward-flexed postures. Secondarily, the authors examined the effects of gender and forward-flexed posture as well as their interactions with lead use., Background: The use of a lead is mandatory for interventionalists during surgical procedures. Because the vest portion of a lead weighs considerably more than normal clothing, there is concern that its use increases the risk of developing back and shoulder pain., Method: In a repeated-measures study design, 19 young healthy male and female adults assumed standardized erect or forward-flexed postures, both with and without wearing the vest portion of a lead. Shoulder and lower back muscle activity was measured via surface electromyography, normalized by maximum voluntary contraction values. Data were analyzed using general linear models and repeated-measures ANOVA (significant for p < .05)., Results: Use of the lead did not result in a significant increase in muscle activity in the lower back or shoulders, despite perceived increases in effort and discomfort. Posture proved to be the most significant secondary factor affecting activity in the lower back, and participant gender proved insignificant., Conclusion: Short-term use of the lead does not appear to contribute to the incidence of back pain or injury in interventionalists. Avoiding flexed postures could more directly reduce the likelihood of pain or injury., Application: Potential applications include assessing and improving operating room ergonomics for physicians.

We hypothesize that the CNS detects a loss of balance by comparing outputs predicted by a nominal, forward internal model with actual sensory outputs. When the resulting control error signal reaches an anomalously large value, this control error anomaly (CEA) signals a loss of balance and precedes any observable compensatory response. To test this hypothesis, a multi-input, multi-output internal model of a standing forward reach task was developed that incorporated on-line model identification and a Gaussian failure detection algorithm. Eleven healthy young women were then asked to stand and reach forward to a target positioned from 95 to 125% of their maximum reach distance. Kinematic and kinetic data were recorded at 100 Hz unilaterally from the upper body, leg, and foot. Evidence of successful CEA detection was a compensatory step between 100 ms and 2 s later. The results show that use of a threshold, set at 3 SD from the mean, on error in the control of leg segment acceleration detected a CEA and correctly predicted a compensatory response in 92.6% of 108 trials. Leg acceleration control error was a better predictor than upper body or foot acceleration control error (P = 0.000). CEA detection performed more reliably than loss of balance detection algorithms based on kinematic thresholds (P = 0.000). The results support the hypothesis that a loss of balance may be identified via the use of a nominal forward internal model and probabilistic error monitoring.

The initiation of a single compensatory step in response to balance perturbations has been predicted with accuracies of up to 71%. We sought to determine whether similar methods also could be used to predict the onset of additional compensatory steps in both healthy and balance-impaired older females. Anterior and posterior waist pulls of five different magnitudes were applied to 13 unimpaired young (mean age 23 years), 12 unimpaired older (mean age 71 years), and 15 balance-impaired older (mean age 76 years) women. Body segment kinematic data were recorded at 100 Hz. A step was predicted when the time for the center-of-mass to reach the vertical projection of the boundary of the base-of-support fell below a certain threshold. The results show that 83% of all steps and non-steps were correctly predicted at an optimal time-to-boundary threshold (tau(opt)) of 0.78 s. Step prediction accuracy did not differ significantly by group: 86% of steps and non-steps by young, 84% by unimpaired old, and 82% by balance-impaired old women were correctly predicted at tau(opt) of 0.58, 0.67, and 0.78 s, respectively. Anterior steps and non-steps were predicted more accurately than posterior ones (94% vs. 79% correct at tau(opt) of 0.52 and 0.84 s, respectively) and initial steps were better predicted than additional ones (87% vs. 81% correct at tau(opt) of 0.77 and 0.34 s, respectively). We conclude that this step prediction method reasonably predicts initial and additional steps in the anterior and posterior direction by all three subject cohorts.

An effective stepping response is often critical in avoiding a fall. Our objective was to study the effects of age and balance impairment on anterior and posterior compensatory stepping strategies in response to waist pull perturbations of 1-5% body weight (BW). Based on maximal unipedal stance time (UST), we tested 15 balance-impaired old (BI, UST < 10s, mean age = 76 years), 12 healthy old (O, UST>30s, mean age = 71 years), and 13 healthy young women (Y, UST >30s, mean age=23 years). Randomized anterior and posterior pulls of 1-5% body weight (BW) were applied to the waist while kinematic and kinetic recovery responses were recorded. Results show that O and BI required 0.5 more steps than Y to recover balance for posterior pulls of 4-5% BW (P < 0.01). For anterior pulls of 4-5% BW, only BI had a greater probability of step initiation (P

Background: Most falls are attributed to a loss of balance without a quantitative definition of the term. It has been proposed that a loss of balance is detectable as an unusually large (anomalous) value of the system control error. The hypotheses were tested that age will not affect the detection of control error anomaly, or prediction of the associated compensatory response, in a challenging balancing task., Methods: Twenty healthy older adults were asked to sit and balance a chair over its rear legs for as long as possible. The dominant foot's ground reaction force and the chair's sagittal-plane acceleration represented the system input and output, respectively. Control error was the difference between actual and expected acceleration output from a self-identified forward internal model of the system. A control error anomaly was detected once the error crossed a threshold set at three standard deviations (3-Sigma) above the mean of baseline data. Results from five trials were compared to published results in 20 healthy young adults. FINDINGs. A control error anomaly was successfully detected in 91% of 91 older adult trials, statistically similar to the 92% success rate obtained previously in young adults. A response was predicted in 57% of the 77 older adult trials with responses, significantly less than the 92% obtained in the young adult trials (age effect significant: P<0.005)., Interpretation: The condition leading to uncontrolled backward acceleration of the chair was reliably detected in both groups. While the young waited to respond to this condition, older subjects responded prematurely.

Standing turns are associated with an increased risk for falls and fall-related injuries in the elderly. The purpose of this study was to test the (null) hypothesis that age has no effect on the kinematics of the 180 degrees turn. Ten young and 10 older healthy women were asked to complete a series of 180 degrees turns in a standing posture after picking up a light bowl with both hands. Foot-ground reactions, insole pressures and body segment kinematics were recorded in 62 trials at 100 Hz. Turning strategies were analyzed for effects of both age and turn direction on linear and angular foot kinematics, as well as pelvic axial rotation. The older women (OW) used a preparatory stepping strategy more often (170%, p < 0.002), and employed a lower average pelvic rotation rate (21%, p < 0.011) than the younger controls. The minimum foot separation distance for OW was less in their non-preferred than in their preferred turn direction (29%, p < 0.038), thereby increasing their risk of foot-foot interference and falling when turning in their non-preferred direction. The older women were more variable in their turn execution, particularly in minimum foot separation distance (55%, p < 0.022) and the maximum rate of pelvic rotation (82%, p < 0.035). Despite the fact that these healthy older women were careful to employ a preparatory stepping strategy and slower average rotational velocities, they were also more variable in their turn execution than the young.

Objective: This study was undertaken to quantify resting vaginal closure force (VCF(REST)), maximum vaginal closure force (VCF(MAX)), and augmentation of vaginal closure force augmentation (VCF(AUG)) when supine and standing and to determine whether the change in intra-abdominal pressure associated with change in posture accounts for differences in VCF., Study Design: Thirty-nine asymptomatic, continent women were recruited to determine, when supine and standing, the vaginal closure force (eg, the force closing the vagina in the mid-sagittal plane) and bladder pressures at rest and at maximal voluntary contraction. VCF was measured with an instrumented vaginal speculum and bladder pressure was determined with a microtip catheter. VCF(REST) was the resting pelvic floor tone, and VCF(MAX) was the peak pelvic floor force during a maximal voluntary contraction. VCF(AUG) was the difference between VCF(MAX) and VCF(REST). T tests and Pearson correlation coefficients were used for analysis., Results: VCF(REST) when supine was 3.6 +/- 0.8 N and when standing was 6.9 +/- 1.5 N--a 92% difference (P < .001). The VCF(MAX) when supine was 7.5 +/- 2.9 N and when standing was 10.1 +/- 2.4 N--a 35% difference (P < .001). Bladder pressure when supine (10.5 +/- 4.7 cm H2O) was significantly less (P < .001) than when standing (31.0 +/- 6.4 cm H2O). The differences in bladder pressure when either supine or standing did not correlate with the corresponding differences in VCF at rest or at maximal voluntary contraction. The supine VCF(AUG) of 3.9 +/- 2.7 N, was significantly greater than the standing VCF(AUG) of 3.3+/-1.9 N., Conclusion: With change in posture, vaginal closure force increases because of higher intra-abdominal pressure and greater resistance in the pelvic floor muscles.

Given that a physical definition for a loss of balance (LOB) is lacking, the hypothesis was tested that a LOB is actually a loss of effective control, as evidenced by a control error signal anomaly (CEA). A model-reference adaptive controller and failure-detection algorithm were used to represent central nervous system decision-making based on input and output signals obtained during a challenging whole-body planar balancing task. Control error was defined as the residual generated when the actual system output is compared with the predicted output of the simple first-order polynomial system model. A CEA was hypothesized to occur when the model-generated control error signal exceeded three standard deviations (3sigma) beyond the mean calculated across a 2-s trailing window. The primary hypothesis tested was that a CEA is indeed observable in 20 healthy young adults (ten women) performing the following experiment. Seated subjects were asked to balance a high-backed chair for as long as possible over its rear legs. Each subject performed ten trials. The ground reaction force under the dominant foot, which constituted the sole input to the system, was measured using a two-axis load cell. Angular acceleration of the chair represented the one degree-of-freedom system output. The results showed that the 3sigma algorithm detected a CEA in 94% of 197 trials. A secondary hypothesis was supported in that a CEA was followed in 93% of the trials by an observable compensatory response, occurring at least 100 ms later, and an average of 479 ms, later. Longer reaction times were associated with low velocities at CEA, and vice versa. It is noteworthy that this method of detecting CEA does not rely on an external positional or angular reference, or knowledge of the location of the system's center of mass., (Copyright 2003 Elsevier B.V.)

Objective: To test the working hypotheses that after a brief (10 min) intervention, (a) young adults can volitionally reduce fall-related wrist impact forces, and (b) no difference in impact force would exist between intervention and control groups at 3-weeks or 3-months follow-up., Background: The wrist is the most commonly fractured site in the body at any age, most often as a result of impact with the ground while arresting a forward fall.Methods. Twenty-nine healthy young male volunteers participated. A 3-month intervention group (n=10) performed five standardized forward falls before and after a 10-min instructional intervention aimed at reducing wrist impact forces during the baseline visit. They, along with a 3-month control group (n=11) who did not receive the intervention, were remeasured in five trials at 3-weeks and 3-months follow-up, without intervening practice. A baseline control group (n=8) performed the five trials, then repeated them at the baseline visit without receiving the intervention. Unilateral body segment kinematics and bilateral hand-ground impact forces were measured and the hypotheses were tested using repeated measures analysis of variance., Results: At the baseline visit, a significant group-by-trial-block interaction was found (P=0.02): the 3-month intervention group reduced their average maximum impact forces by 18% from initial values (P=0.002); the baseline control group did not do so (0.5% increase, P=0.91). The 3-month intervention (20 falls) and control (15 falls) groups did not differ at the 3-month follow-up (P=0.62); however, when the groups were combined their maximum impact force had decreased significantly (8.9%, P=0.04) over that time., Conclusions: Healthy young males learned in 10 min to significantly reduce wrist impact forces in forward falls, but retention was poor at 3-weeks follow-up. Irrespective of group, however, after the 5 falls at 3-weeks subjects had taught themselves to reduce their impact forces at the 3-months follow-up., Relevance: A brief educational intervention can significantly reduce forward fall-related impact forces in the short term. However, with or without the brief intervention, the experience of performing between 5-10 forward falls 3 weeks apart apparently resulted in decreased impact forces over the next 2 months, thereby reducing the risk of injury in these forward falls.

Objective: This study tried to isolate critical biomechanical factors in fall arrests using the upper extremity during simulated forward falls. This study also attempted to find the differences in those factors between young and old age groups., Background: The role of the upper extremity is not well defined despite its primary usage as a local shock absorber during fall impact., Design: Comparative study in which two age groups underwent motion analysis.Methods. Ten healthy older males (mean age, 66.4 years) and 10 young males (mean age, 24.1 years) volunteered to perform self-initiated and cable-released falls at selected falling distances, while the joint motion and impact forces at the hand were recorded., Results: Significant age differences were demonstrated in joint kinematics and impact force parameters at close distances. Excessive reflexive responses of the upper extremity in cable-released falls for the older adults resulted in 10-15 times higher peak impact forces and 2-3 times shorter body braking time than in self-initiated falls., Conclusions: Pre-impact activities of the upper extremity predispose the post-impact response during fall arrests. Suppressing excessive pre-impact reflexive activation of the arms could efficiently decrease the risk of fall-related injuries, which calls for securing sufficient arm movement time. Any fall prevention strategy that can increase arm movement time would be effective against injuries of the upper extremity during falling in the older adults., Relevance: The findings will help to understand underlying mechanisms of fall arrest using the upper extremity for prevention of fall-related fractures.

Objective: To test the hypotheses (1) that the maximum distance reached by young or older women when standing on a raised platform is independent of movement speed, and (2) the maximum forward momentum generated at comfortable and fast reaching speeds is independent of age., Design: Repeated measures case-control study in a university laboratory setting.Background. Maximum forward reach distance is often part of a geriatric mobility assessment. The effect of movement speed, and hence momentum, on forward reaching behavior is unknown in young or older subjects, despite the fact that excess momentum might increase the risk of fall-related injuries, especially from an elevated surface., Methods: Ten healthy young women (mean age 23.7 years) and 10 healthy older women (mean age 70.5 years) participated. Subjects stood on an instrumented force platform and forward reach body segment kinematics were measured optoelectronically. Whole-body center of reaction and center of mass trajectories were calculated during six maximum forward reach trials: three performed "at a comfortable speed", and three performed "as fast as possible"., Results: Subjects reached slightly further at a comfortable speed than when reaching as fast as possible (P=0.016). Fast reaches were associated with a 25% increase in momentum (P<0.001; however, under both speed conditions, older women developed less whole-body momentum than did young controls (for example, 4.1 vs. 6.1 kgm/s at comfortable speed, P<0.05). Three young and one older women lost their balance in at least one trial., Conclusions: Independent of age, these women reached further when reaching slowly than when reaching rapidly, and older women restricted peak forward momentum under both speed conditions when standing on the elevated surface., Relevance: Interventions designed to reduce falls from raised surfaces might utilize the insights gained from these women that (1) at any age, one cannot expect to reach as far when reaching fast as one can when reaching slowly; and (2) comfortable reaching speed is reduced in older individuals.

This study examined the association between the measured amount of urine lost during a standardized series of coughs in clinic (paper towel test) and questionnaire estimates of stress-related urine loss in 51 older women with mild to moderate urinary incontinence. It also examined the relationship between these questionnaire estimates and a 6-day urinary diary self-report of incontinence frequency and voiding episodes. Pearson's correlation coefficient and percent agreement were used to analyze the relationship between the variables. No significant correlations were found between the paper towel test results and questionnaire items reporting volume of urine loss. The relationship between urinary diary results and questionnaire items regarding the number of incontinence occurrences was weak but significant (r = 0.33, p = 0.045), with agreement in 53% of cases. Agreement was achieved in 68% of cases for number of voids per day recorded by urinary diary and reported by questionnaire (r = 0.65, p = 0.000). This study has quantified a weak correlation between objective and subjective measures of urine loss. These weak correlations could arise from either methodologic limitations in quantifying incontinence or the degree to which differences arise because different phenomena are being measured.

Background: Previous work has found that healthy older men were significantly less able than young male adults to recover balance by taking a single rapid step upon sudden release from forward leans. In light of the higher rates of falls and fall-related injuries among older women compared to older men, we hypothesized that healthy older women would perform more poorly than either female young adults or older men in this test of abilities to recover balance rapidly., Methods: Ten young (mean age 25.0 years) and 10 older (73.7 years) healthy women were released from forward leans and instructed to regain standing balance by taking a single step forward. The lean angle was incrementally increased from its smallest value, approximately 14 degrees, until the subject failed to regain balance as instructed. Lower extremity kinematics were measured, and findings were compared with those of the earlier study of healthy young and old men., Results: Five of the 10 older women could not recover balance with a single step after release from the smallest of the imposed forward leans. For the 5 older women who succeeded in recovering as instructed from at least one lean, the mean maximum lean angle was significantly smaller than that for young women (16.2 degrees vs 30.7 degrees, p < .001) or older men (16.2 degrees vs 23.9 degrees, p = .014). In contrast, there was no significant difference in mean maximum lean angle between female and male young adults., Conclusions: Healthy older women, compared to either young women or older men, were significantly less able to recover balance by taking a single rapid step during a forward fall. The decreased abilities of older women appeared to result from limitations in the maximum speeds at which they moved their swing foot during recovery.

Background: The objective of this study was to determine in healthy young and old adult females the influence of age, rotation direction, angle, and speed on the threshold for sensing foot dorsi- and plantarflexion when standing and bearing weight on the limb., Methods: Twelve young (YF, mean age 22 years) and 12 old (OF, 70 years) healthy adult females stood with their dominant foot on a servo-controlled platform and the other foot on a fixed platform. The platform induced either dorsi- or plantarflexion rotations at angular velocities of 0.1, 0.5, or 2.5 degrees/s to angles of 0.05, 0.1, 0.2, 0.4 or 0.8 degree. Subjects performed five trials at each velocity-angle combination and 30 dummy trials in which no platform rotation occurred, for a total of 180 trials. Success rates were determined for detecting both rotation (SRR) and rotation direction (SRD) for each test condition. The angular thresholds required to achieve an SRD of 75% were estimated using logistic regression., Results: Age, rotation angle, and rotation speed significantly affected SRD (repeated measures ANOVA: p < .001). For the YF, DF thresholds were 0.04, 0.09, and 0.41 degree at the fast, moderate, and slow velocities, respectively. Threshold angles were three to four times larger in the OF than in the YF. A 10-fold reduction in the angular threshold was observed upon increasing the speed of rotation from 0.1 to 2.5 degrees/s., Conclusions: Both age and speed significantly affected the thresholds for sensing foot dorsiflexion and plantarflexion in women.

A randomized quadruple staircase method and probit analysis were used to measure the thresholds for sensation of ankle inversion and eversion by 18 healthy young and 18 healthy old subjects while standing with a foot in a servo-driven cradle. The results of over 3600 trials show that the mean threshold for detecting inversion with a probability of 75% was 0.35 degrees in the older subjects, a value significantly greater than the 0.06 degrees threshold found in the younger group. The corresponding thresholds in eversion were significantly greater in both old (0.52 degrees) and young (0.35 degrees) subjects. Significant, but smaller, age differences were also found in unipedal stance. Few significant sex differences were found. When the velocity of a 0.1 degree inversion movement was increased from 2 to 200 degrees/s the probability of detecting it rose by only 22.6%. Although significantly increased with age, the threshold for sensing rotation in the weight-bearing ankle was measured in tenths of degrees, an order of magnitude better than previously reported (non-weight-bearing) values.

Quantification of the biomechanical factors that underlie the inability to rise from a chair can help explain why this disability occurs and can aid in the design of chairs and of therapeutic intervention programs. Experimental data collected earlier from 17 young adult and two groups of elderly subjects, 23 healthy and 11 impaired, rising from a standard chair under controlled conditions were analyzed using a planar biomechanical model. The joint torque strength requirements and the location of the floor reaction force at liftoff from the seat in the different groups and under several conditions were calculated. Analyses were also made of how body configurations and the use of hand force affect these joint torques and reaction locations. In all three groups, the required torques at liftoff were modest compared to literature data on voluntary strengths. Among the three groups rising with the use of hands, at the time of liftoff from the seat, the impaired old subjects, on an average, placed the reaction force the most anterior, the healthy old subjects placed it intermediately and the young subjects placed it the least anterior, within the foot support area. Moreover, the results suggest that, at liftoff, all subjects placed more importance on locating the floor reaction force to achieve acceptable postural stability than on diminishing the magnitudes of the needed joint muscle strengths.

Trunk proprioception was measured in 253 healthy children 7-18 years of age using infrared markers placed on the back of the head and on the skin over the T1, T8, and S1 spinous processes. The children were tested for their accuracy in sensing return of the head and trunk to a centered, neutral position in the frontal plane. Whole-body sway was also quantified during 10 s of relaxed standing by measuring mean amplitudes of trunk marker and foot center of pressure (CP) movements. The results show that trunk positioning accuracy improved significantly with age (p = 0.000). Subjects could position their trunk in the frontal plane to within a mean (+/- SD) of 2.5 (+/- 1.1) and 0.9 (+/- 0.6) degrees of the neutral position at ages 7 and 18 years, respectively. No statistically significant gender differences were found. At every age trunk positioning accuracy was diminished in the presence of a continuous external trunk moment (equivalent to 0.01 x body weight x height), although not significantly so. Neither mean trunk sway nor CP amplitudes were significantly correlated with age or sex. The overall results suggest that spine decompensation is only abnormal when it exceeds 20 mm in healthy children and adolescents.