Sandra C. Webber

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.

Knee strength deficits after hamstring tendon and patellar tendon anterior cruciate ligament reconstruction.

PURPOSE The purpose of this study was to examine the strength of the knee flexors and knee extensors after two surgical techniques of ACL reconstruction and compare them to an age and activity level matched control group. METHODS Twenty-four subjects who had undergone ACL reconstruction greater than 1 yr previously were placed into one of two groups according to autograft donor site: patellar tendon (BPB; N = 8) and hamstring (H; N = 16), and compared with an active, control group (N = 30). Knee flexor and extensor strength was evaluated using isovelocity dynamometry (5 speeds, eccentric and concentric, 5-95 degrees ROM). Strength maps were used to graphically analyze strength over a broad operational domain of the neuromuscular system. Average strength maps were determined for each autograft group and compared with controls. A difference map (control minus graft group) and confidence (t-test) maps were used to quantitatively identify strength deficits. RESULTS The combined ACL group (N = 24) revealed a global 25.5% extensor strength deficit, with eccentric regional (angle and velocity matched) deficits up to 50% of control. Strength deficits covered over 86% of the sampled strength map area (P < 0.01). These knee extensor strength deficits are greater than previously reported. In addition, the BPB group demonstrated a concentric, low velocity, knee extensor strength deficit at 60-95 degrees that was not observed in the H group. Significant graft site dependent, regional knee flexor deficits of up to 50% of control were observed for the H group. CONCLUSIONS Strength deficits localized to specific contraction types and ranges of motion were demonstrated between the ACL and control groups that were dependent upon autograft donor site. Postoperative rehabilitation protocols specific to these deficits should be devised.

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.

Hamstring and quadriceps strength balance in normal and hamstring anterior cruciate ligament-reconstructed subjects.

Objective:The purpose of this study was to evaluate and characterize the agonist-antagonist strength balance (hamstring/quadriceps [H/Q] ratio and dynamic control ratio [DCR]) about the knee specific to velocity, range of motion, and contraction type. We hypothesized that there would be systematic variation in the H/Q ratio and DCR based on knee joint angle, angular velocity, and contraction type. We also hypothesized that these ratios would be altered in the anterior cruciate ligament (ACL)-reconstructed group in favor of protecting the ACL graft (relative knee flexor strength when strain on the ACL is the greatest). Design:Cross-sectional design. Setting:A tertiary care sport medicine clinic. Patients or Participants:Sixteen subjects more than 1 year after hamstring tendon ACL reconstruction were compared with 30 active uninjured control subjects. Interventions:Isokinetic strength testing was performed over 5° to 95° knee joint range of motion, 5 angular velocities (50, 100, 150, 200, 250°/s), for concentric and eccentric contractions. Main Outcome Measurements:Angle and velocity-matched H/Q ratio maps and DCR maps were produced for each group. Difference maps allowed quantification of the differences between the groups. Results:Angle and velocity-matched H/Q ratio maps demonstrated systematic variation based on joint angle, velocity, and contraction type for both the control (H/Q, ~0–1.42; DCR, ~0–1.57) and the ACL-reconstructed group (H/Q, ~0–1.33; DCR, ~0–1.35). Difference maps demonstrate regional (angle and velocity-specific) alteration in the ratio between the ACL-reconstructed and control groups. Conclusions:Specific imbalances were demonstrated in the ACL-reconstructed group compared with control. In high knee flexion angles, the low H/Q ratio may represent a compromised ability of the hamstrings to stabilize the knee joint throughout the full range of motion. Near full knee extension shifts in favor of the knee flexors may represent an attempt to stabilize the knee at the angle of greatest ACL strain. These finding have implications for graft donor site selection and postoperative rehabilitation as well as provide insight into the neuromuscular control of the knee.

Effect of ActiGraph GT3X+ Position and Algorithm Choice on Step Count Accuracy in Older Adults

Accelerometer step count accuracy may be affected by gait speed, device positioning, and analysis algorithm selection. We assessed ActiGraph GT3X+ step count accuracy related to device placement and analysis algorithm in older adults with walking aids (n = 13) and without walking aids (n = 22). Participants (81.5 ± 5.0 years of age) completed a timed 100-m walk wearing five GT3X+ monitors (hips, ankles, lumbar spine). Individuals with walking aids had slower gait speeds (0.8 ± 0.20 m/s versus 1.2 ± 0.20 m/s without walking aids, p < .001). Intraclass correlation coefficient values for observed versus monitored steps were highest when ankle placement and the low frequency extension (LFE) algorithm were used (left ankle ICC = .989, right ankle ICC = .998). Using the GT3X+ ankle placement and analyzing data with the LFE algorithm resulted in the most accurate step counts in older adults.

Modeling age-related neuromuscular changes in humans

With aging, motoneurons and muscle tissue undergo significant changes, which influence function in terms of strength, mobility, and overall independence. Mathematical modeling provides a practical method of studying the relationships among recruitment, rate-coding, and force output in motor units, and may be used to predict functional neuromuscular changes related to aging. For this study, the Heckman-Binder model was used to examine changes in human quadriceps motor units. Relationships among current input, firing frequency, and force output were defined for both a younger and an older individual. Included in the model were age-related effects associated with reduced muscle contractile speed; reduced muscle-fibre number, size, and specific tension; reduced gain of the frequency-current relationship; decreased size of motoneurons; and altered motor unit remodeling. Adjustment of this model to reflect age-related changes resulted in a leftward shift of the force-frequency function, lower firing frequency for any given current injected into the motoneuron, and a reduction in maximal force output. The model suggests that older individuals are capable of reaching force levels up to approximately 50% of those attained by younger individuals, with relatively similar or even slightly lower levels of current input. This could mean that the sense of effort and the contribution of factors other than degree of effort from afferent inputs to the pool, including conscious supraspinal centres, might be different in the older adult.

Sedentary Behavior, Cadence, and Physical Activity Outcomes after Knee Arthroplasty.

Purpose This study comprehensively examined sedentary behavior and physical activity patterns in people with severe knee osteoarthritis awaiting total knee arthroplasty (TKA) and in individuals after TKA. Methods Preoperative (n = 32, mean ± SD = 69.9 ± 5.3 yr) and 1-yr postoperative participants with TKA (n = 38, 67.9 ± 7.3 yr) wore ActiGraph GT3X+ activity monitors for 6.8 ± 0.6 d. Total sedentary time, time in long sedentary bouts (≥30 min), and physical activity outcomes (steps, time in moderate-to-vigorous physical activity [MVPA], cadence) were examined. Results There were no differences between pre- and postoperative groups for total sedentary time (9.3 ± 1.4 vs 9.2 ± 1.4 h·d−1, P = 0.62) and number of long sedentary bouts per day (median [interquartile range] = 3.4 [1.9] vs 3.1 [2.0], P = 0.37). Daily steps, peak 30-min cadence, and peak 1-min cadence values were greater in people after TKA compared with those awaiting surgery (5935 [3316] vs 3724 [2338], 55.6 [31.0] vs 35.9 [19.3], and 91.5 ± 20.6 vs 70.0 ± 23.7, respectively, all P < 0.01). There were no differences in lifestyle MVPA between groups. The number of bouts of Freedson MVPA was greater in postoperative participants, but the differences were not substantial (one bout per week). Conclusion Patients report less knee pain and improved function after TKA; however, sedentary behavior does not differ and physical activity is only marginally increased compared with those awaiting surgery. After TKA, daily walking at slow, moderate, and brisk paces and engagement in MVPA do not match levels seen in healthy older adults, which, when combined with high levels of sedentary behavior, leaves patients at increased risk for physical disability and cardiovascular disease.