Biomedical subjects

James A Ashton-Miller

Publications and source records attributed to James A Ashton-Miller.

At least 19 recordsLinked to original sources

PubMed2006

What causes a crossover step when walking on uneven ground? A study in healthy young women.

We hypothesized that, during gait, the perturbation caused by stepping on a 1.2-cm high protuberance with the medial forefoot would not only alter stance foot kinematics and kinetics, but also alter subsequent step location and timing, even to the point of causing a crossover step. Twelve healthy young women performed at least three flat surface and three perturbation trials while walking along a level walkway. To obstruct visual monitoring of their upcoming foot placement they used both hands to carry a large tray in front of their abdomen. Kinematic data from optoelectronic markers and force plate data were recorded at 50 and 100Hz, respectively. The results showed that the medial forefoot perturbation significantly decreased the net ankle eversion moment (p<0.001) and increased the maximum inversional foot acceleration (p=0.007). Step width (SW) and time (ST) of the post-perturbation recovery step were significantly decreased compared with normal steps (p=0.002 and 0.049, respectively). The maximum inversional foot acceleration correlated negatively with SW and ST of the recovery step (both p=0.001). Finally, four of 36 (12%) recovery steps were crossover steps. We conclude that a medial forefoot perturbation results in an increased inversional acceleration of the stance foot followed by a decrease in recovery SW and ST. In some cases, a medial forefoot perturbation can result in a crossover step, an extreme form of a narrow recovery step.

Adult↗

PubMed2006

A kinematic analysis of the rapid step test in balance-impaired and unimpaired older women.

Little is known about the kinematic and kinetic determinants that might explain age and balance-impairment alterations in the results of volitional stepping performance tests. Maximal unipedal stance time (UST) was used to distinguish "balance-impaired" old (BI, UST<10s, N=15, mean age=76 years) from unimpaired old (O, UST>30s, N=12, mean age=71 years) before they and healthy young females (Y, UST>30s, N=13, mean age=23 years) performed the rapid step test (RST). The RST evaluates the time required to take volitional front, side, and back steps of at least 80% maximum step length in response to verbal commands. Kinematic and kinetic data were recorded during the RST. The results indicate that the initiation phase of the step was the major source of age- and balance impairment-related delays. The delays in BI were primarily caused by increased postural adjustments prior to step initiation, as measured by center-of-pressure (COP) path length (p<0.003). The Step landing phase showed similar, but non-significant, temporal trends. Step length and peak center-of-mass (COM) deceleration during the Step-Out landing decreased in O by 18% (p=0.0002) and 24% (p=0.001), respectively, and a further 12% (p=0.04) and 18% (p=0.08) in BI. We conclude that the delay in BI step initiation was due to the increase in their postural adjustments prior to step initiation.

Adult↗

PubMed2006

The effect of an impulsive knee valgus moment on in vitro relative ACL strain during a simulated jump landing.

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.

Aged↗

PubMed2006

Obstetric factors associated with levator ani muscle injury after vaginal birth.

OBJECTIVE: To identify obstetric factors associated with development of levator ani injury after vaginal birth. METHODS: Magnetic resonance images were taken of the pelvic floor of 160 women 9 to 12 months after first term vaginal delivery. Half the women had de novo stress incontinence and half were continent controls. Abnormalities of the pubovisceral portion were identified on magnetic resonance as present or absent. Defect severity was further scored in each muscle from 0 (no defect) to 3 (complete muscle loss). A summed score for the 2 sides (0 to 6) was assigned and grouped as minor (0-3) or major (4-6). Obstetric details were collected. The association between obstetric variables and muscle injury were analyzed using Fisher exact test and t tests. RESULTS: The following increased odds ratios for levator defect were found: forceps use 14.7 (95% confidence interval [CI] 4.9-44.3), anal sphincter rupture 8.1 (95% CI 3.3-19.5) and episiotomy 3.1 (95% CI 1.4-7.2) but not vacuum delivery 0.9 (95% CI 0.19-4.3), epidural use 0.9 (95% CI 0.4-2.0), or oxytocin use 0.8 (95% CI 0.3-1.8). Women with levator injury were 3.5 years older and had a 78-minute longer second stage of labor. Differences in gestational age, birth weight, and head circumference were not statistically significant. A major defect in the pubovisceral muscle was seen in 22 women and a minor defect in 7 women. CONCLUSION: Injuries to the levator ani muscles in women after their first vaginal delivery are associated with several obstetric factors indicating difficult vaginal birth and with older age. LEVEL OF EVIDENCE: II-3.

Adult↗

PubMed2006

Interaction among apical support, levator ani impairment, and anterior vaginal wall prolapse.

OBJECTIVE: To use a biomechanical model to explore how impairment of the pubovisceral portion of the levator ani muscle, the apical vaginal suspension complex, or both might interact to affect anterior vaginal wall prolapse severity. METHODS: A biomechanical model of the anterior vaginal wall and its support system was developed and implemented. The anterior vaginal wall and its main muscular and connective tissue support elements, namely the levator plate, pubovisceral muscle, and cardinal and uterosacral ligaments were included, and their geometry was based on midsagittal plane magnetic resonance scans. Material properties were based on published data. The change in the sagittal profile of the anterior vaginal wall during a maximal Valsalva was then predicted for different combinations of pubovisceral muscle and connective tissue impairment. RESULTS: Under raised intra-abdominal pressure, the magnitude of anterior vaginal wall prolapse was shown to be a combined function of both pubovisceral muscle and uterosacral and cardinal ligament ("apical supports") impairment. Once a certain degree of pubovisceral impairment was reached, the genital hiatus opened and a prolapse developed. The larger the pubovisceral impairment, the larger the anterior wall prolapse became. A 90% impairment of apical support led to an increase in anterior wall prolapse from 0.3 cm to 1.9 cm (a 530% increase) at 60% pubovisceral muscle impairment, and from 0.7 cm to 2.4 cm (a 240% increase) at 80% pubovisceral muscle impairment. CONCLUSION: These results suggest that a prolapse can develop as a result of impairment of the muscular and apical supports of the anterior vaginal wall.

Biometry↗

PubMed2006

Quantification of levator ani cross-sectional area differences between women with and those without prolapse.

OBJECTIVE: Compare levator ani cross-sectional area as a function of prolapse and muscle defect status. METHODS: Thirty women with prolapse and 30 women with normal pelvic support were selected from an ongoing case-control study of prolapse. For each of the two groups, 10 women were selected from three categories of levator defect severity: none, minor, and major identified on supine magnetic resonance scans. Using those scans, three-dimensional (3D) models of the levator ani muscles were made using a modeling program (3D Slicer), and cross-sections of the pubic portion were calculated perpendicular to the muscle fiber direction using another program, I-DEAS. An analysis of variance was performed. RESULTS: The ventral component of the levator muscle of women with major defects had a 36% smaller cross-sectional area, and women with minor defects had a 29% smaller cross-sectional area compared with the women with no defects (P < .001). In the dorsal component, there were significant differences in cross-sectional area according to defect status (P = .03); women with major levator defects had the largest cross-sectional area compared with the other defect groups. For each defect severity category (none, minor, major), there were no significant differences in cross-sectional area between women with and those without prolapse. CONCLUSION: Women with visible levator ani defects on magnetic resonance imaging had significantly smaller cross-sectional areas in the ventral component of the pubic portion of the muscle compared with women with intact muscles. Women with major levator ani defects had larger cross-sectional areas in the dorsal component than women with minor or no defects. LEVEL OF EVIDENCE: II-2.

Case-Control Studies↗

PubMed2006

Stepping onto raised, laterally compliant structures: a biomechanical study of age and gender effects in healthy adults.

OBJECTIVE: To investigate the effects of gender and age on the kinematics and kinetics associated with stepping onto, and balancing on, a raised structure with lateral compliance. BACKGROUND: Falls from a stepladder tipping sideways are associated with considerable socioeconomic costs. METHOD: Ten young women (YF) and 10 young men (YM), aged 23 to 29 years, and 10 older men (OM) aged 66 to 75 years were asked to step up onto one of two raised structures with increasing lateral compliance (C1 and C2), presented in sets of six trials separated by up to 12 rigid (C0) structure trials. RESULTS: Structural compliance (C1 or C2) significantly affected step duration (p < .05) and lateral weight transfer velocity (p < .01). Significant age (p < .001) and gender (p < .05) differences were found in step duration and center of mass adjustments: With increasing structural compliance, participants required more time (YM: 15%; YF ranged from 33% to 45%; OM 35%-37%) to complete the step-up movement. CONCLUSION: Increasing age and structural compliance were both associated with larger and longer-lasting structural oscillations that increase the risk for a lateral fall. APPLICATION: Older adults, in particular, should not hurry their movements on raised structures. Actual or potential applications of this research include additional safety instructions for ladder users and considerations of structural compliance for designers and authors of national or international standards for raised structures.

Accidental Falls↗

PubMed2005

The relationship between quadriceps muscle force, knee flexion, and anterior cruciate ligament strain in an in vitro simulated jump landing.

BACKGROUND: An instrumented cadaveric knee construct was used to quantify the association between impact force, quadriceps force, knee flexion angle, and anterior cruciate ligament relative strain in simulated unipedal jump landings. HYPOTHESIS: Anterior cruciate ligament strain will correlate with impact force, quadriceps force, and knee flexion angle. STUDY DESIGN: Descriptive laboratory study. METHODS: Eleven cadaveric knees (age, 70.8 [19.3] years; 5 male; 6 female) were mounted in a custom fixture with the tibia and femur secured to a triaxial load cell. Quadriceps, hamstring, and gastrocnemius muscle forces were simulated using pretensioned steel cables (stiffness, 7 kN/cm), and the quadriceps tendon force was measured using a load cell. Mean strain on the anteromedial bundle of the anterior cruciate ligament was measured using a DVRT. With the knee in 25 degrees of flexion, the construct was vertically loaded by an impact force initially directed 4 cm posterior to the knee joint center. Tibiofemoral kinematics was measured using a 3D optoelectronic tracking system. RESULTS: The increase in anterior cruciate ligament relative strain was proportional to the increase in quadriceps force (r(2) = 0.74; P < .00001) and knee flexion angle (r(2) = 0.88; P < .00001) but was not correlated with the impact force (r(2) = 0.009; P = .08). CONCLUSION: The increase in knee flexion and quadriceps force during this simulated 1-footed landing strongly influenced the relative strain on the anteromedial bundle of the anterior cruciate ligament. CLINICAL RELEVANCE: These results suggest that even in the presence of knee flexor muscle forces, the increase in quadriceps force required to prevent the knee from flexing during landing can place the anterior cruciate ligament at risk for large strains.

Aged↗

PubMed2005

Can initial and additional compensatory steps be predicted in young, older, and balance-impaired older females in response to anterior and posterior waist pulls while standing?

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.

Accidental Falls↗

PubMed2005

Factors affecting stepladder stability during a lateral weight transfer: a study in healthy young adults.

A fall from a stepladder is often initiated by a loss of lateral stability. An inverted pendulum model of the human, validated by experiment, was used to determine the feasible range of whole-body center of mass (COM) states for which weight can be transferred laterally on a ladder tread without a ladder rail losing contact with the ground ("no lift-off" stability region). The results show that the size of the feasible no lift-off region was inversely proportional to the height of the tread above the ground, the distance of the stance foot from the ipsilateral rail, and lateral ground inclination angle. For given initial COM kinematics on a tread height equal to 40% human body height, a stance-foot location equal to one-eighth tread width and a 3.5 degrees ground inclination had approximately equivalent effects on the no lift-off region size. Ladder stability was three times more sensitive to tread height than to foot location. Laterally-exerted impulsive hand-tool forces should generally be limited to 8% body weight. These findings can lead to improved ladder designs and safety instructions for stepladder users.

Accidental Falls↗

PubMed2005

Does vaginal closure force differ in the supine and standing positions?

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.

Adult↗

PubMed2005

Pudendal nerve stretch during vaginal birth: a 3D computer simulation.

OBJECTIVE: The purpose of this study was to determine the increase in pudendal nerve branch lengths using a 3D computer model of vaginal delivery. STUDY DESIGN: The main inferior rectal and perineal branches of the pudendal nerve were dissected in 12 hemi-pelves from 6 adult female cadavers. Their 3D courses were digitized in the 4 specimens with the most characteristic nerve branching pattern, and the data were imported into a published 3D computer model of the pelvic floor. Each nerve branch was then represented by a stretchable cord with a fixation point at the ischial spine. The length change in each branch was then quantified as the fetal head descended through the pelvic floor. The maximum nerve strains ([final length minus original length/original length] x 100) were calculated for 5 degrees of perineal descent: reference descent from the literature, 1.25 cm and 2.5 cm caudal and cephalad. The effect of alternative fixation points on resultant nerve strain was also studied. RESULTS: The inferior rectal branch exhibited the maximum strain, 35%, and this strain varied by 15% from the scenario with the least perineal descent to that with the most perineal descent. The strain in the perineal nerve branch innervating the anal sphincter reached 33%, while the branches innervating the posterior labia and urethral sphincter reached values of 15% and 13%, respectively. The more proximal the nerve fixation point, the greater the nerve strain. CONCLUSION: During the second stage: (1) nerves innervating the anal sphincter are stretched beyond the 15% strain threshold known to cause permanent damage in appendicular peripheral nerve, and (2) the degree of perineal descent is shown to influence pudendal nerve strain.

Aged↗

PubMed2005

Gait analysis in a challenging environment differentiates between fallers and nonfallers among older patients with peripheral neuropathy.

OBJECTIVE: To identify differences in gait based on fall history among a group of older subjects with peripheral neuropathy (PN) in 2 environments: standard (SE) (smooth surface, normal lighting) and challenging (CE) (irregular surface, low lighting). DESIGN: Observational, case-control study of PN subjects with and without a history of falling in the previous year. SETTING: A biomechanical laboratory. PARTICIPANTS: Forty-two subjects (mean age, 64.7+/-9.8 y; 20 [47.6%] women), including 22 (52.4%) with a history of at least 1 fall in the previous year. INTERVENTION: Subjects walked in the SE and CE while kinematic data were obtained. MAIN OUTCOME MEASURES: Step width variability, step time variability, step width-to-step length ratio, step length, and step time and speed (with step length and speed normalized for height) in the SE and CE. RESULTS: In the SE, gait parameters of subjects with and without a history of falls did not differ significantly. However, in the CE, subjects with a history of falls had increased step time variability (P=.001). Moreover, significant interactions between environment and fall status were identified: in the CE, subjects with a history of falls had greater increases in step time variability (P=.010) and step width-to-step length ratio (P=.009) and greater decreases in step length (P=.007) and speed (P=.045) than did subjects with no fall history. CONCLUSIONS: Analysis of gait in the CE and adjustment to the CE from the SE effectively identified gait characteristics associated with falls in an older PN population, whereas analysis of gait in the SE did not. PN-associated gait dysfunction is more sensitively detected on an irregular rather than on a flat surface.

Accidental Falls↗

PubMed2005

Effect of age on detecting a loss of balance in a seated whole-body balancing task.

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.

Adaptation, Physiological↗

PubMed2005

Effects of surface irregularity and lighting on step variability during gait: a study in healthy young and older women.

Relatively few studies have examined how uneven surfaces affect human gait. To study this, along with the effects of advancing age and low light conditions, we measured step width and step time variability, as well as comfortable gait speed, in 12 healthy young women (YW) and 12 healthy older women (OW) as they walked at a comfortable speed along a 10-m walkway. Ten trials were completed for each cell of a 2 x 2 factorial design: (1) flat surface with regular lighting; (2) flat surface with low lighting; (3) irregular surface with regular lighting; and (4) irregular surface with low lighting. Effects of surface type, incident lighting, and age on gait parameters were tested via repeated measures ANOVA. Surface type significantly affected step width variability (P < 0.001) and step time variability (P < 0.001). Light level showed no significant effect on any of the gait parameters. One significant age group difference was found: step width variability was significantly greater in OW than YW (P = 0.010). We conclude that the irregular surface had a greater effect on the gait variability of healthy OW than on that of healthy YW.

Adult↗

PubMed2005

Influence of an irregular surface and low light on the step variability of patients with peripheral neuropathy during level gait.

Patients with peripheral neuropathy (PN) report greater difficulty walking on irregular surfaces with low light (IL) than on flat surfaces with regular lighting (FR). We tested the primary hypothesis that older PN patients would demonstrate greater step width and step width variability under IL conditions than under FR conditions. Forty-two subjects (22 male, 20 female: mean +/- S.D.: 64.7 +/- 9.8 years) with PN underwent history, physical examination, and electrodiagnostic testing. Subjects were asked to walk 10 m at a comfortable speed while kinematic and force data were measured at 100 Hz using optoelectronic markers and foot switches. Ten trials were conducted under both IL and FR conditions. Step width, time, length, and speed were calculated with a MATLAB algorithm, with the standard deviation serving as the measure of variability. The results showed that under IL, as compared to FR, conditions subjects demonstrated greater step width (197.1 +/- 40.8 mm versus 180.5 +/- 32.4 mm; P < 0.001) and step width variability (40.4 +/- 9.0 mm versus 34.5 +/- 8.4 mm; P < 0.001), step time and its variability (P < 0.001 and P = 0.003, respectively), and step length variability (P < 0.001). Average step length and gait speed decreased under IL conditions (P < 0.001 for both). Step width variability and step time variability correlated best under IL conditions with a clinical measure of PN severity and fall history, respectively. We conclude that IL conditions cause PN patients to increase the variability of their step width and other gait parameters.

Accidental Falls↗

PubMed2005

Kinematic analyses of the 180 degrees standing turn: effects of age on strategies adopted by healthy young and older women.

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.

Adult↗

PubMed2005

Age differences in timed accurate stepping with increasing cognitive and visual demand: a walking trail making test.

BACKGROUND: Impaired vision, cognition, and divided attention performance predict falls. Requiring both visual and cognitive input, the ability to step accurately is necessary to safely traverse challenging terrain conditions such as uneven or slippery surfaces. We compared healthy young and older adults in the time taken to step accurately under conditions of increasing cognitive and visual demand. METHODS: Healthy Young (n = 42, mean age 21) and Older (n = 37, mean age 70) participants were required to step accurately on an instrumented walkway under conditions of increasing visual and cognitive demand. Based on the paper-and-pencil neuropsychological test, the Trail Making Test (P-TMT) A and B, participants stepped on instrumented targets with increasing sequential numbers (Walking Trail Making Test A [W-TMT A]) and increasing sequential numbers and letters (Walking Trail Making Test B [W-TMT B]), under conditions of Low as well as Normal lighting. RESULTS: W-TMT performance time increased with increased age (Older vs Young), decreased light (Low vs Normal), and increased cognitive demand (Trails B vs Trails A). W-TMT performance time was disproportionately increased in Low light and in the Older group under the highest cognitive demand (W-TMT B) conditions. Paired W-TMT A-B differences were three times higher in the Older group than in the Young group. In the Older group, the correlation between W-TMT results and P-TMT B was particularly strong (p <.001). CONCLUSIONS: The time to perform a stepping accuracy task, such as may be required to avoid environmental hazards, increases under reduced lighting and with increased cognitive demand, the latter disproportionately so in older adults.

Adolescent↗