Michelle M. Porter

Mobility in Older Adults: A Comprehensive Framework

Mobility is fundamental to active aging and is intimately linked to health status and quality of life. Although there is widespread acceptance regarding the importance of mobility in older adults, there have been few attempts to comprehensively portray mobility, and research has to a large extent been discipline specific. In this article, a new theoretical framework for mobility is presented with the goals of raising awareness of the complexity of factors that influence mobility and stimulating new integrative and interdisciplinary research ideas. Mobility is broadly defined as the ability to move oneself (e.g., by walking, by using assistive devices, or by using transportation) within community environments that expand from ones home, to the neighborhood, and to regions beyond. The concept of mobility is portrayed through 5 fundamental categories of determinants (cognitive, psychosocial, physical, environmental, and financial), with gender, culture, and biography (personal life history) conceptualized as critical cross-cutting influences. Each category of determinants consists of an increasing number of factors, demonstrating greater complexity, as the mobility environment expands farther from the home. The framework illustrates how mobility impairments can lead to limitations in accessing different life-spaces and stresses the associations among determinants that influence mobility. By bridging disciplines and representing mobility in an inclusive manner, the model suggests that research needs to be more interdisciplinary and current mobility findings should be interpreted more comprehensively, and new more complex strategies should be developed to address mobility concerns.

Correspondence between self-reported and objective measures of driving exposure and patterns in older drivers

The driving behavior of older adults has been traditionally examined using questionnaires and diaries. The accuracy of self-reports has been questioned, and in-vehicle recording devices touted as more objective measures of real-world driving. The purposes of this study were to replicate and extend prior research comparing self-report and actual measures of driving exposure and patterns. Two electronic devices were installed in the vehicles of 61 drivers (67-92 years, 59% women) who were instructed to drive as usual over 1-week. Participants completed trip logs, daily diaries, a questionnaire on usual driving habits, ratings of situational driving frequency and avoidance and a follow-up interview. Only 53% of the sample attempted to estimate how far they had driven over the week and self-estimates were inaccurate (ME=77.5 km; CV=44.5%). Drivers tended to miss a significant number of trips and stops in their diaries. Driving behavior over the week was fairly consistent with usual practices regarding time of day, driving in certain areas, and night driving. However, subjects drove in challenging situations more than usual. Triangulating multiple sources of electronic and self-reported data provided a better understanding about the behavior of older drivers.

Predicting Driving Performance in Older Adults: We Are Not There Yet!

Objective. We set up this study to determine the predictive value of approaches for which a statistical association with driving performance has been documented. Methods. We determined the statistical association (magnitude of association and probability of occurrence by chance alone) between four different predictors (the Mini-Mental State Examination, Trails A test, Useful Field of View [UFOV], and a composite measure of past driving incidents) and driving performance. We then explored the predictive value of these measures with receiver operating characteristic (ROC) curves and various cutoff values. Results. We identified associations between the predictors and driving performance well beyond the play of chance (p < .01). Nonetheless, the predictors had limited predictive value with areas under the curve ranging from .51 to .82. Conclusions. Statistical associations are not sufficient to infer adequate predictive value, especially when crucial decisions such as whether one can continue driving are at stake. The predictors we examined have limited predictive value if used as stand-alone screening tests.

Reliability of Ankle Isometric, Isotonic, and Isokinetic Strength and Power Testing in Older Women

Background Ankle strength (force-generating capacity) and power (work produced per unit of time or product of strength and speed) capabilities influence physical function (eg, walking, balance) in older adults. Although strength and power parameters frequently are measured with dynamometers, few studies have examined the reliability of measurements of different types of contractions. Objective The purpose of this study was to examine relative and absolute intrarater reliability of isometric, isotonic, and isokinetic ankle measures in older women. Design This was a prospective, descriptive methodological study. Methods The following dorsiflexion (DF) and plantar-flexion (PF) measures were assessed twice (7 days apart) by the same examiner in 30 older women (mean age=73.3 years, SD=4.7): isometric peak torque and rate of torque development (RTD), isotonic peak velocity, average acceleration and peak power, and isokinetic peak torque and peak power (30°/s and 90°/s). Several statistical methods were used to examine relative and absolute reliability. Results Intraclass correlation coefficients (ICCs) for the DF tests (ICC=.76–.97) were generally higher than ICCs for matched PF tests (ICC=.58–.93). Measures of absolute reliability (eg, coefficient of variation of the typical error [CVTE]) also demonstrated more reliable values for DF tests (5%–18%) compared with PF tests (7%–37%). Isotonic peak velocity tests at minimal loads were associated with the lowest CVTE and ratio limits of agreement values for both DF (5% and 14%, respectively) and PF (7% and 18%, respectively). Isometric RTD variables were the least reliable (CVTE=16%–37%). Limitations This study was limited to a relatively homogeneous sample of older women. Conclusions Test-retest reliability was adequate for determining changes at the group level for all strength and power variables except isometric RTD. Minimal detectable change scores were determined to assist clinicians in assessing meaningful change over time in ankle strength and power measurements within individuals.

Validation of an Electronic Device for Measuring Driving Exposure

Objective. This study sought to evaluate an on-board diagnostic system (CarChip) for collecting driving exposure data in older drivers. Methods. Drivers (N = 20) aged 60 to 86 years from Winnipeg and surrounding communities participated. Information on driving exposure was obtained via the CarChip and global positioning system (GPS) technology on a driving course, and obtained via the CarChip and surveys over a week of driving. Velocities and distances were measured over the road course to validate the accuracy of the CarChip compared to GPS for those parameters. Results. The results show that the CarChip does provide valid distance measurements and slightly lower maximum velocities than GPS measures. From the results obtained in this study, it was determined that retrospective self-reports of weekly driving distances are inaccurate. Conclusions. Therefore, an on-board diagnostic system (OBDII) electronic device like the CarChip can provide valid and detailed information about driving exposure that would be useful for studies of crash rates or driving behavior.

Pedestrians' Normal Walking Speed and Speed When Crossing a Street

Walking speed is a key input for various traffic engineering applications. This paper presents the results of research conducted over 18 months to understand the difference between the normal and the crossing walking speeds of pedestrians at signalized intersections and to determine the effect of seasonality on walking speed, taking into account age and gender. For the purposes of this paper, normal walking speed is the speed at which pedestrians walk without needing to cross an intersection, and crossing walking speed is that at which pedestrians walk when they are crossing a signalized intersection. The research found that in all cases the normal walking speed is less than the crossing walking speed. It also found that younger pedestrians walk faster than older pedestrians, regardless of the season and gender, and females walk slower than males, regardless of the season and age. Furthermore, both younger and older pedestrians have a greater normal walking speed in summer than in winter but a lower crossing walking speed in winter than in summer. In addition, the research also found that by use of a design value of 1.2 m/s (4.0 ft/s), as recommended in the current Manual of Uniform Traffic Control Devices, nearly two-thirds of older pedestrians would be excluded in the design process on the basis of their normal walking speed and about 40% would be excluded on the basis of their crossing walking speed. The design value of 1.2 m/s (4.0 ft/s) excludes nearly one-third of younger pedestrians on the basis of their normal walking speed and about 10% on the basis of their crossing walking speed.

Strength training in old age: Adaptation of antagonist muscles at the ankle joint

The purpose of this study was to determine whether strength training could reduce the deficit in plantarflexion (PF) maximal voluntary contraction (MVC) torque observed in previous studies in older subjects relative to young adults. Accordingly, the effects of a 6‐month strength training program on the muscle and neural properties of the major muscle groups around the ankle were examined. PF and dorsiflexion (DF) isometric MVC torques were measured and surface electromyographic activity of the triceps surae and tibialis anterior muscles was recorded. The strength training program was very effective in improving strength in PF (+24.5%), and it thus reduced the DF‐to‐PF MVC torque ratio; in addition, it also induced gains in DF (+7.6%). Thus, there must be an improvement in ankle joint stability. In PF, gains were due particularly to a modification of the agonist neural drive; in DF, the gains appeared to be the consequence of a reduction in antagonist coactivation. Our findings indicate that the investigation of one muscle group should always be accompanied by examination of its antagonist muscle group. Muscle Nerve, 2005

The relationship between cognitive performance, perceptions of driving comfort and abilities, and self-reported driving restrictions among healthy older drivers

The objective of the present study was to examine the relationship between cognitive performance, driver perceptions and self-reported driving restrictions. A cross-sectional analysis was conducted on baseline data from Candrive II, a five-year prospective cohort study of 928 older drivers aged 70-94 years from seven cities. Cognitive performance was assessed using the Montreal Cognitive Assessment (MoCA) as well as the Trail Making Test, parts A and B. Driver perceptions were assessed using the Day and Night Driving Comfort Scales and the Perceived Driving Abilities scale, while driving practices were captured by the Situational Driving Frequency and Avoidance scales, as well as the Driving Habits and Intentions Questionnaire. The baseline data indicates this cohort is largely a cognitively intact group. Univariate regression analysis showed that longer Trails A and B completion times were significantly, but only modestly associated with reduced driving frequency and perceived driving abilities and comfort, as well as a significant tendency to avoid more difficult driving situations (all p<.05). Most of these associations persisted after adjusting for age and sex, as well as indicators of health, vision, mood and physical functioning. Exceptions were Trails A and B completion times and situational driving frequency, as well as time to complete Trails B and current driving restrictions. After adjusting for the confounding factors, the total MoCA score was not associated with any of the driving measure scores while the number of errors on Trails A was significantly associated only with situational driving frequency and number of errors on Trails B was significantly associated only with situational driving avoidance. Prospective follow-up will permit examination of whether baseline cognition or changes in cognition are associated with changes in driver perceptions, actual driving restrictions and on-road driving outcomes (e.g., crashes, violations) over time.

Biopsy sampling requirements for the estimation of muscle capillarization

The aim of this study was to determine the number of tibialis anterior biopsy samples and muscle fibers required to estimate the capillary supply of individual muscle fibers (C:Fi). C:Fi was calculated for 25 type 1 fibers in each of 8 images from 3 biopsies of 5 young healthy individuals. Sequential estimation analysis indicated that 50 fibers from one biopsy are sufficient to characterize the C:Fi of the tibialis anterior for a group of subjects. Thus, when analyzing the capillarization of the tibialis anterior, the requirements of only one biopsy sample and 50 fibers means a great reduction in time for analysis and in the invasiveness of the procedure.

A method of measuring standing isokinetic plantar and dorsiflexion peak torques.

Different methods have been used for concentric (CONC) isokinetic testing of ankle dorsiflexion (DF) and plantar flexion (PF). However, little information is available on either the reliability of these protocols or eccentric (ECC) torque production. As well, previous studies utilized non-weight-bearing test positions. The purpose of this study was to develop a reliable method of testing CONC and ECC DF and PF in a weight-bearing position. One group of adults, including older men and women were tested on two occasions with a standing protocol. Another group of older and younger men and women were compared between the standing method and a supine protocol. For both positions the velocity was 30 degrees.s-1 for the CONC and ECC actions, and the range of motion was 10 degrees DF to 20 degrees PF. Reliability coefficients for peak torque (PT) were acceptable and ranged from 0.65 to 0.90. The two testing positions were significantly related (r = 0.84-0.91), but CONC PT in standing were greater than supine. Therefore, this method of testing isokinetic DF and PF in a standing position has acceptable reliability and produces results consistent with those acquired with the supine protocol. It provides a means of comparing groups and examining intervention strategies while weight-bearing.