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Background: Measurements of pelvic floor muscle strength are contaminated by crosstalk from intra-abdominal pressure. We tested an improved instrumented speculum designed to minimize this crosstalk. The hypotheses were that the speculum yields: 1) maximum vaginal closure forces unrelated to intra-abdominal pressure, 2) discriminatory validity between women with strong vs. weak pelvic floor muscles, and 3) acceptable test-retest reliability., Methods: Maximum voluntary vaginal closure force was measured in 40 incontinent women (20-77 years) on two visits spaced one month apart. At the baseline visit, intra-abdominal pressure was also estimated via intra-vesical catheterization during the vaginal closure force measurement. Subjective estimate of pelvic floor muscle strength was also assessed using digital palpation by a skilled examiner to determine group placement as "strong" (n=31) or "weak" (n=9)., Findings: Vaginal closure force was not significantly correlated with intra-abdominal pressure (r=-.26, P=.109). The groups with subjectively scored strong and weak pelvic floor muscles differed significantly by mean [SD] maximum vaginal closure force (3.8 [1.7] vs. 1.9 [0.8] N respectively, P<.01.) Across both time points the mean vaginal closure force was 3.42 [1.67] N with a range of .68 to 9.05 N. Mean Visit 1 and Visit 2 vaginal closure force scores did not differ (3.41 [1.8] and 3.42 [1.6] N, respectively). The vaginal closure force repeatability coefficient was 3.1N., Interpretation: The improved speculum measured maximum vaginal closure force without evidence of crosstalk from intra-abdominal pressure, while retaining acceptable discriminant validity and repeatability., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

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.)

Background: Fall-related injuries are multifaceted problems. One approach to identify the critical biomechanical factors is biodynamic simulation., Methods: A 2-degree-of-freedom discrete impact model was constructed through system identification and validated using experimental data in order to understand the dynamic interactions of various biomechanical parameters in bimanual forward fall arrests., Findings: The bimodal reaction force responses from the identified models had very small identification errors (<3.5%) and high coherence (R(2)=0.95) between the measured and identified model responses. Model validation with separate experimental data also demonstrated excellent validation accuracy and coherence, less than 7% errors and R(2)=0.87, respectively. The first force peak was usually greater than the second force peak and strongly correlated with the impact velocity of the upper extremity, while the second force peak was associated with the impact velocity of the body. The impact velocity of the upper extremity relative to the body could be a major risk factor to fall-related injuries as observed from model simulations that a 75% faster arm movement relative to the falling speed of the body alone could double the first force peak from that of a soft landing, thereby readily exceeding the fracture strength of the distal radius., Interpretation: Despite the time-critical nature of falling often calling for a rapid arm movements, the safe use of the upper extremity in forward fall arrests requires adequate reaction times and coordinated protective motions of the upper extremity.

Background: Maximum step length (MSL) is a clinical test that has been shown to correlate with age, various measures of fall risk, and knee and hip joint extension speed, strength, and power capacities, but little is known about the kinematics and kinetics of the large out-and-back step utilized., Methods: Body motions and ground reaction forces were recorded for 11 unimpaired younger and 10 older women while attaining maximum step length. Joint kinematics and kinetics were calculated using inverse dynamics. The effects of age group and step length on the biomechanics of these large out-and-back steps were determined., Findings: Maximum step length was 40% greater in the younger than in the older women (P<0.0001). Peak knee and hip, but not ankle, angle, velocity, moment, and power were generally greater for younger women and longer steps. After controlling for age group, step length generally explained significant additional variance in hip and torso kinematics and kinetics (incremental R2=0.09-0.37). The young reached their peak knee extension moment immediately after landing of the step out, while the old reached their peak knee extension moment just before the return step liftoff (P=0.03)., Interpretation: Maximum step length is strongly associated with hip kinematics and kinetics. Delays in peak knee extension moment that appear to be unrelated to step length, may indicate a reduced ability of older women to rapidly apply force to the ground with the stepping leg and thus arrest the momentum of a fall.

Background: Increased step time variability, particularly on an irregular surface, has been associated with impaired mobility function and a variety of diseases. However the biomechanical necessity, or advantage, of increasing step time variability has not been identified., Methods: We performed a secondary analysis of gait data previously obtained on 42 subjects age 50 or older with neuropathy who walked on smooth and irregular surfaces, the latter with and without three interventions (cane, ankle orthosis and wall touch) that provided frontal plane support., Findings: Step time variability on smooth and irregular surfaces was most strongly associated with reduction in step length on the irregular surface as compared to the smooth. More specifically, the greater the decrease in step length on the irregular surface the greater the step time variability on both surfaces and the greater the increase in step time variability on the irregular surface. The increase in step length on the irregular surface afforded by the interventions coincided with a decrease in step time variability. The subjects did not simultaneously demonstrate increased step time variability and step width range on the irregular surface., Interpretation: Among adults age 50 and older with neuropathy, increased step time variability is strongly associated with the need to shorten step length on an irregular surface. Therefore step time variability may be a marker for instability during single limb stance which necessitates rapidly placed, shortened recovery steps. Such steps may also offer the advantage of reducing extremes in lateral foot placement of the swing limb, and so assist in maintaining frontal plane stability.

Background: Maximum Step Length may be used to identify older adults at increased risk for falls. Since leg muscle weakness is a risk factor for falls, we tested the hypotheses that maximum knee and hip extension speed, strength, and power capacities would significantly correlate with Maximum Step Length and also that the "step out and back" Maximum Step Length [Medell, J.L., Alexander, N.B., 2000. A clinical measure of maximal and rapid stepping in older women. J. Gerontol. A Biol. Sci. Med. Sci. 55, M429-M433.] would also correlate with the Maximum Step Length of its two sub-tasks: stepping "out only" and stepping "back only". These sub-tasks will be referred to as versions of Maximum Step Length., Methods: Unimpaired younger (N=11, age=24[3]years) and older (N=10, age=73[5]years) women performed the above three versions of Maximum Step Length. Knee and hip extension speed, strength, and power capacities were determined on a separate day and regressed on Maximum Step Length and age group. Version and practice effects were quantified and subjective impressions of test difficulty recorded. Hypotheses were tested using linear regressions, analysis of variance, and Fisher's exact test., Findings: Maximum Step Length explained 6-22% additional variance in knee and hip extension speed, strength, and power capacities after controlling for age group. Within- and between-block and test-retest correlation values were high (>0.9) for all test versions., Interpretation: Shorter Maximum Step Lengths are associated with reduced knee and hip extension speed, strength, and power capacities after controlling for age. A single out-and-back step of maximal length is a feasible, rapid screening measure that may provide insight into underlying functional impairment, regardless of age.

Background: We tested the hypothesis that impulsive compression, flexion and valgus knee moment loading during a simulated one-footed jump landing will significantly increase the peak relative strain in the anteromedial region of the anterior cruciate ligament compared with loading without the valgus moment., Methods: Ten cadaveric knees [mean (SD) age: 67.9 (7.6) years; 5 males; 5 females] were mounted into a custom fixture to simulate a lower extremity impact loading of approximately 1600 N. Triaxial load cells monitored the 3D tibial and femoral impulsive force and moments at 2000 Hz, while 3D tibiofemoral kinematics were measured at 400 Hz. Pre-impact quadriceps, hamstring and gastrocnemius muscle forces were simulated using pretensioned steel cables. A differential variable reluctance transducer measured the relative strain in the anteromedial aspect of the anterior cruciate ligament. With the knee initially in 25 degrees flexion, 10 trials were conducted with the impulsive force directed 4 cm posterior to the knee joint center in the sagittal plane ("neutral" loading) to cause a flexion moment, 10 trials were conducted under a similar loading, but with the force directed 15 degrees lateral to the knee sagittal plane ("valgus" loading), and the 10 neutral loading trials were then repeated. A non-parametric Wilcoxon signed rank test was used to test the hypothesis using a P<0.05 significance level., Findings: The peak normalized anterior cruciate ligament strain was 30% larger for the impulsive compression loading in valgus and flexion compared with an impulsive compression loading in isolated flexion (P<0.05)., Interpretation: Minimizing the abduction loading of the knee during a jump landing should help reduce anterior cruciate ligament strain during that maneuver.

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.

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.

Objective: To evaluate the effect of age and diabetic neuropathy on ankle motor function in the frontal plane in terms of rate of torque development and capability for balance recovery., Design: Case control study. Six older women with diabetic neuropathy compared to six women without neuropathy, matched for age and presence of diabetes mellitus; and nine healthy young women., Background: Neuropathy causes a distal impairment in lower extremity sensory function which increases fall risk. Impairments in ankle inversion/eversion proprioceptive thresholds have been identified, but the effect of neuropathy on ankle motor strength in the frontal plane is unknown., Methods: Subjects' abilities to recover from a lateral lean (with center of gravity offset as percentage of foot width) while standing on one foot, and to rapidly generate inversion torque about the ankle, were quantified., Results: All nine of the young, but only one of six older, control subjects recovered from a 10% lean (P=0.0052). Three of six older controls, but no neuropathy subject, recovered from a 5% lean (P=0.083). Neuropathy subjects demonstrated half the ankle rate of torque development [78.2 (50.8) N m/s; P=0.016] of the young and older controls [162.0 (54.6) and 152.7 (22.2) N m/s, respectively]., Conclusions: Diabetic neuropathy leads to a decrease in rapidly available ankle strength which impairs balance recovery among older women. Younger women demonstrate similar ankle strength but superior balance recovery compared to older women without neuropathy.