Physical Behavior Profiles Among Older Adults and Their Associations With Physical Capacity and Life-Space Mobility.

We identified data-driven multidimensional physical activity (PA) profiles using several novel accelerometer-derived metrics. Participants aged 75, 80, and 85 (n = 441) wore triaxial accelerometers for 3-7 days. PA profiles were formed with k-means cluster analysis based on PA minutes, intensity, fragmentation, sit-to-stand transitions, and gait bouts for men and women. Associations with physical capacity and life-space mobility were examined using age-adjusted general linear models. Three profiles emerged: "Exercisers" and "actives" accumulated relatively high PA minutes, with actives engaging in lighter intensity PA. "Inactives" had the highest activity fragmentation and lowest PA volume, intensity, and gait bouts. Inactives showed lower scores in physical capacity and life-space mobility compared with exercisers and actives. Exercisers and actives had similar physical capacity and life-space mobility, except female exercisers had higher walking speed in the 6-min walk test. Our findings demonstrate the importance of assessing PA as multidimensional behavior rather than focusing on a single metric.

The Impact of Multimorbidity Patterns on Changes in Physical Activity and Physical Capacity Among Older Adults Participating in a Year-Long Exercise Intervention.

This study investigated the impact of multimorbidity patterns on physical activity and capacity outcomes over the course of a year-long exercise intervention, and on physical activity 1 year later. Participants were 314 physically inactive community-dwelling men and women aged 70-85 years, with no contraindications for exercise at baseline. Physical activity was self-reported. Physical capacity measurements included five-time chair-stand time, 6-minute walking distance, and maximal isometric knee-extension strength. The intervention included supervised and home-based strength, balance, and walking exercises. Multimorbidity patterns comprised physician-diagnosed chronic disease conditions as a predictor cluster and body mass index as a measure of obesity. Multimorbidity patterns explained 0%-12% of baseline variance and 0%-3% of the change in outcomes. The magnitude and direction of the impact of unique conditions varied by outcome, time point, and sex. Multimorbid older adults with no contraindications for exercise may benefit from multimodal physical training.

Assessment of Ground Contact Time in the Field: Evaluation of Validity and Reliability.

ABSTRACT: Weber, JA, Hart, NH, Rantalainen, T, Connick, M, and Newton, RU. Assessment of ground contact time in the field: evaluation of validity and reliability. J Strength Cond Res 38(1): e34-e39, 2024-The capacity to measure the kinetic and kinematic components of running has been extensively investigated in laboratory settings. Many authors have produced work that is of high value to practitioners within sporting environments; however, the lack of field-based technology to assess features of running gait validly and reliably has prevented the application of these valuable works. This paper examines the validity and reliability of a practical field-based methodology for using commercial inertial measurement units (IMUs) to assess ground contact time (GCT). Validity was examined in the comparison of GCT measured from ground reaction force by a force plate and that determined by a lumbar mounted commercial IMU and analyzed using a commercially available system (SPEEDSIG). Reliability was assessed by a field-based examination of within and between-session variability in GCT measured using a commercially available system (SPEEDSIG). Significance was set at p ≤ 0.05. Results for validity (intraclass correlation [ICC] 0.83) and reliability (ICC 0.91) confirm that the described field-based methodology is qualified for use to determine GCT in a practical setting. The implications of this study are important as they offer sport practitioners (S&C coaches, rehab specialists, and physios) a scalable method to assess GCT in the field to develop greater understanding of their athletes and improve performance, injury prevention, and rehabilitation interventions. Furthermore, these results provide the foundation for further work that could provide greater detail describing individual running gait in the field.

Physical activity and cognitive function: moment-to-moment and day-to-day associations.

BACKGROUND: The beneficial effect of acute physical exercise on cognitive performance has been studied in laboratory settings and in long-term longitudinal studies. Less is known about these associations in everyday environment and on a momentary timeframe. This study investigated momentary and daily associations between physical activity and cognitive functioning in the context of everyday life. METHODS: Middle-aged adults (n = 291, aged 40-70) were asked to wear accelerometers and complete ecological momentary assessments for eight consecutive days. Processing speed and visual memory were assessed three times per day and self-rated evaluations of daily cognition (memory, thinking, and sharpness of mind) were collected each night. The number of minutes spent above the active threshold (active time) and the maximum vector magnitude counts (the highest intensity obtained) before each cognitive test and at a daily level were used as predictors of momentary cognitive performance and nightly subjective cognition. Analyses were done with multilevel linear models. The models were adjusted for temporal and contextual factors, age, sex, education, and race/ethnicity. RESULTS: When participants had a more active time or higher intensity than their average level within the 20 or 60 minutes prior to the cognitive test, they performed better on the processing speed task. On days when participants had more active time than their average day, they rated their memory in the evening better. Physical activity was not associated with visual memory or self-rated thinking and sharpness of mind. CONCLUSIONS: This study provides novel evidence that outside of laboratory settings, even small increases in physical activity boost daily processing speed abilities and self-rated memory. The finding of temporary beneficial effects is consistent with long-term longitudinal research on the cognitive benefits of physical activity.

Bone-specific physical activity questionnaire-derived skeletal loading score predicts bone geometry, density, and strength indices: a cross-sectional study.

INTRODUCTION: The bone-specific physical activity questionnaire (BPAQ) provides a bone-relevant index of physical activity participation according to the mechanical loads experienced across the life span. MATERIALS AND METHODS: We aimed to examine relationships between historical bone-relevant physical activity and pQCT-derived parameters of bone strength. We recruited 532 healthy volunteers (277 males, 255 females) across a broad age range (4-97 years). Peripheral quantitative computed tomography (XCT-3000, Stratec, Germany) was used to examine volumetric bone density, area, and strength indices of the non-dominant tibia and radius. Exercise loading history from birth was determined using the past BPAQ (pBPAQ) score. Pearson correlation analysis was used to examine relationships between pBPAQ scores and pQCT parameters. RESULTS: Independent of sex, pBPAQ scores were associated with total density at the 38% and 66% tibial sites and the 66% radial site (r = 0.145-0.261, p ˂ 0.05), total area at the 38% tibial site and 4% and 66% radial sites (r = 0.129-0.156, p ˂ 0.05), and strength indices at all measured sites (r = 0.123-0.234, p < 0.05). CONCLUSION: We conclude that, independent of sex, historical bone-relevant physical activity is associated with pQCT-derived indices of bone strength, indicating that pBPAQ captures the characteristics of bone loading history that are likely to be relevant adaptive stimuli. A larger sample is required to examine the influence of age on this relationship.

Metabolic health, menopause, and physical activity-a 4-year follow-up study.

BACKGROUND: In women, metabolic health deteriorates after menopause, and the role of physical activity (PA) in mitigating the change is not completely understood. This study investigates the changes in indicators of metabolic health around menopause and evaluates whether PA modulates these changes. METHODS: Longitudinal data of 298 women aged 48-55 years at baseline participating in the ERMA and EsmiRs studies was used. Mean follow-up time was 3.8 (SD 0.1) years. Studied indicators of metabolic health were total and android fat mass, waist circumference, waist-to-hip ratio (WHR), systolic (SBP) and diastolic (DBP) blood pressure, blood glucose, triglycerides, serum total cholesterol, and high- (HDL-C) and low-density (LDL-C) lipoprotein cholesterol. PA was assessed by accelerometers and questionnaires. The participants were categorized into three menopausal groups: PRE-PRE (pre- or perimenopausal at both timepoints, n = 56), PRE-POST (pre- or perimenopausal at baseline, postmenopausal at follow-up, n = 149), and POST-POST (postmenopausal at both timepoints, n = 93). Analyses were carried out using linear and Poisson mixed-effect models. RESULTS: At baseline, PA associated directly with HDL-C and inversely with LDL-C and all body adiposity variables. An increase was observed in total (B = 1.72, 95% CI [0.16, 3.28]) and android fat mass (0.26, [0.06, 0.46]), SBP (9.37, [3.34, 15.39]), and in all blood-based biomarkers in the PRE-POST group during the follow-up. The increase tended to be smaller in the PRE-PRE and POST-POST groups compared to the PRE-POST group, except for SBP. The change in PA associated inversely with the change in SBP (-2.40, [-4.34, -0.46]) and directly with the change in WHR (0.72, [0.05, 1.38]). CONCLUSIONS: In middle-aged women, menopause may accelerate the changes in multiple indicators of metabolic health. PA associates with healthier blood lipid profile and body composition in middle-aged women but does not seem to modulate the changes in most of the studied metabolic health indicators during the menopausal transition.

Accelerometer-based osteogenic indices, moderate-to-vigorous and vigorous physical activity, and bone traits in adolescents.

OBJECTIVES: We investigated the associations of accelerometry-derived osteogenic indices (OIs), moderate-to-vigorous (MVPA), and vigorous intensity physical activity (VPA) with peripheral quantitative computed tomography (pCQT) parameters in 99 adolescents aged 10-13 years. METHODS: Bone parameters were assessed at the distal (4%) and shaft (66%) of the tibia using pQCT. Accelerometers were worn on the right hip for 7 consecutive days. OIs were calculated based on acceleration peak histograms either using all of the peaks (OI) or peaks with acceleration ≥5.2 g (HOI). MVPA and VPA were defined using previously published cut-points. RESULTS: HOI was positively associated with total area (Partial correlation= 0.22, 95% CI=0.01 to 0.41), cortical area (CoA) (0.33, 95% CI=0.13 to 0.50), and stress strain index (SSI) (0.29, 95% CI=0.09 to 0.47) of tibial shaft and with total density at the distal tibia (0.23, 95% CI=0.02 to 0.42). OI was positively associated with CoA (0.31, 95% CI=0.11 to 0.49) and SSI (0.26, 95% CI=0.05 to 0.44) of tibial shaft. MVPA was positively associated with CoA (0.28, 95% CI=0.07 to 0.46) of the tibial shaft. CONCLUSIONS: OI and HOI were positively associated with pQCT parameters while MVPA and VPA demonstrated less consistent associations with them.

Effect of childhood developmental coordination disorder on adulthood physical activity; Arvo Ylppö longitudinal study.

Individuals at risk of Developmental Coordination Disorder (DCD) have low levels of physical activity in childhood due to impaired motor competence; however, physical activity levels in adulthood have not been established. This study sought to determine the impact of DCD risk on physical activity levels in adults using accelerometry measurement. Participants (n = 656) from the Arvo Ylppö Longitudinal Study cohort had their motor competence assessed at the age of five years, and their physical activity quantified via device assessment at the age of 25 years. Between group differences were assessed to differentiate physical activity measures for individuals based on DCD risk status, with general linear modeling performed to control for the effects of sex, body mass index (BMI), and maternal education. Participants at risk of DCD were found to have a lower total number of steps (d = 0.3, p = 0.022) than those not at risk. Statistical modeling indicated that DCD risk status increased time spent in sedentary light activity (ß = 0.1, 95% CI 0.02 to 0.3, p = 0.026) and decreased time spent in vigorous physical activity via interaction with BMI (ß = 0.04, 95% CI 0.001 to 0.1, p = 0.025). Sensitivity analysis found that visuomotor impairment did not significantly impact physical activity but did increase the role of DCD risk status in some models. This 20-year-longitudinal study indicated that DCD risk status continues to negatively impact on levels of physical activity into early adulthood.

Increased Joint Mobility Is Associated With Impaired Transversus Abdominis Contraction.

ABSTRACT: Mitchell, UH, Owen, PJ, Rantalainen, T, and Belavý, DL. Increased joint mobility is associated with impaired transversus abdominis contraction. J Strength Cond Res 36(9): 2472-2478, 2022-Increased joint mobility is a risk factor for joint injury, but muscle function may be able to compensate for it. Current evidence suggests reduced force production capacity in people with hypermobility. However, little is known about the lumbar spine. The purpose of this cross-sectional study was to assess whether there was a link between joint mobility and transverse abdominis and multifidus muscles contraction, muscles ascribed a core-stability role. Using a modified quantitative version of the Beighton scale (BOM score), we measured joint mobility of 30 middle-aged individuals without low back pain. These scores were correlated with magnetic resonance imaging-derived measures of transverse abdominis and multifidus muscle contraction during a spinal loading maneuver. The level of significance was set for p ≤ 0.05. The results showed greater joint mobility (a higher BOM score) correlated ( r = 0.468; p = 0.009) with reduced transversus abdominis (TrA) shortening during contraction (i.e., less muscle shortening in people with greater joint mobility). The trunk subdomain score exhibited a correlation of 0.354 with TrA length change, but this did not reach statistical significance ( p = 0.055). The subdomains of the BOM score did not correlate significantly with each other ( p ≥ 0.097). No association was seen between multifidus contraction and joint mobility. The results suggest that greater general joint mobility is associated with impaired contraction of the TrA muscle. This should be considered when coaching athletes or treating patients with (functional) spinal instability. The quantitative approach we developed to measure joint mobility could be used in the future studies of global flexibility.

Altered prefrontal cortex responses in older adults with subjective memory complaints and dementia during dual-task gait: An fNIRS study.

People with cognitive impairments show deficits during physical performances such as gait, in particular during cognitively challenging conditions (i.e. dual-task gait [DTG]). However, it is unclear if people at risk of dementia, such as those with subjective memory complaints (SMC), also display gait and central deficits associated with DTG. In this study, we investigated the effects of single- and dual-task gait (STG and DTG), on left prefrontal cortex (PFC) activation in elderly people with subjective memory complaints (SMC) and Dementia. A total of 58 older adults (aged 65-94 years; 26 Healthy; 23 SMC; 9 Dementia) were recruited. Gait spatiotemporal characteristics (i.e. stride velocity and length) were assessed using an instrumented walkway during STG and DTG. Single-channel functional near-infrared spectroscopy over the left PFC was used to measure changes in oxyhaemoglobin (O2 Hb) during gait. Stride velocity and length during STG (all p < .05) and DTG (all p < .000) were significantly impaired in people with Dementia compared to Healthy and SMC individuals. No differences were observed between Healthy and SMC. For STG, a greater increase in O2 Hb (p < .05) was observed in those with Dementia compared to the Healthy and SMC, while no differences were observed between Healthy and SMC. A significant increase and decline in O2 Hb was observed during DTG in the SMC and Dementia groups, respectively, compared to Healthy. Our findings indicate an altered pattern of cerebral haemodynamic response of the left PFC in DTG in people with SMC and Dementia, which may suggest that central changes precede functional impairments in people with SMC.

Identifying and Assessing Inter-Muscular Fat at the Distal Diaphyseal Femur Measured by Peripheral Quantitative Computed Tomography (pQCT).

INTRODUCTION: Inter-/intramuscular fat can be assessed with peripheral Quantitative Computed Tomography (pQCT) and is of interest as an indicator of "muscle quality." Typical pQCT scan sites (forearm, lower leg) have a low amount of inter-/intramuscular fat, however distal diaphyseal femur scan sites with conspicuous inter-/intramuscular fat have been identified as potentially more prudent scan sites, even in healthy adolescents. However, current state of the art analysis methods require labor-intensive manual segmentation of the scan. The purpose of the present study was to evaluate the reliability of a novel open source automated enclosing convex polygon approach (source code https://github.com/tjrantal/pQCT, commit cec9bce) to quantify inter-/intramuscular fat from femoral pQCT scans in healthy adults. METHODOLOGY: The distal diaphyseal femur (25% of tibial length from the knee joint towards the hip) of 27 adults aged 18-50 yr were scanned twice, 1 wk apart, using pQCT. Subcutaneous fat, muscle, inter-/intramuscular fat, and marrow areas, and corresponding densities were evaluated using a method we have reported previously, as well as the novel enclosing convex polygon method. RESULTS: The session-to-session reliability of the assessments was fair to excellent using the previously reported method as indicated by intraclass correlation coefficient (ICC2,1) ranging from 0.45 to 1.00, while the novel method produced excellent reliability (ICC2,1 0.78-1.00). CONCLUSION: Distal diaphyseal femur appears to be a potentially informative and prudent scan site for inter-/intramuscular fat evaluation with pQCT.

Count- versus MAD-based accelerometry-assessed movement behaviors and associations with child adiposity and fitness.

Estimations of time spent sedentary and in various physical activity intensities may vary according to data reduction methods applied. This study compared associations between children's accelerometer data and adiposity and fitness markers using open source (mean amplitude deviation, MAD) and proprietary (counts) data reduction methods. Complete-case accelerometer, adiposity (Body Mass Index z-score, waist circumference), and fitness (cardiorespiratory, musculoskeletal) data from 118 children (10.4 ± 0.6 years, 49% girls) were analyzed. Estimates of sedentary behavior, light-, moderate-, vigorous- (VPA), and moderate- to vigorous-intensity (MVPA) physical activity were calculated using count- and MAD-based data reduction methods. Linear regression models between time in movement behaviours and fitness and adiposity markers were conducted. Significant differences in estimates of time spent in all intensities were observed between MAD-based and count-based methods. Both methods produced evidence to suggest that sedentary behavior was detrimentally, and physical activity (any intensity) was beneficially, associated with waist circumference. MVPA and VPA were beneficially associated with fitness markers using both data reduction measures. Overall, findings suggest that estimates of sedentary time and physical activity were not comparable. However, the strength and direction of the associations obtained between the different data reduction methods and adiposity and fitness outcomes were fairly comparable, with both methods finding stronger associations for VPA compared to MVPA. This suggests that future studies may be able to pool data using different data reduction approaches when examining associations between activity and health risk factors, albeit with caution.

Development of a Parkinson's disease specific falls questionnaire.

BACKGROUND: Falls are a major health burden for older adults with Parkinson's disease (PD), but there is currently no reliable questionnaire to capture the circumstances and consequences of falls in older adults with PD. This study aimed to develop a PD-specific falls questionnaire and to evaluate its test-retest reliability in older adults with PD. METHODS: A novel PD-specific falls questionnaire (PDF-Q) was developed in two modes (online and paper-based version) and used to assess falls and near-falls events over the past 12-months. Questions were agreed upon by an expert group, with the domains based on previous falls-related questionnaires. The questions included the number and circumstances (activities, location and direction) of falls and near-falls, and consequences (injuries and medical treatment) of falls. The PDF-Q was distributed to 46 older adults with PD (online n = 30, paper n = 16), who completed the questionnaire twice, 4 weeks apart. Kappa (κ) statistics were used to establish test-retest reliability of the questionnaire items. RESULTS: Pooled results from both questionnaires for all participants were used to assess the overall test-retest reliability of the questionnaire. Questions assessing the number of falls (κ = 0.41) and the number of near-falls (κ = 0.51) in the previous 12-months demonstrated weak agreement, while questions on the location of falls (κ = 0.89) and near-falls (κ = 1.0) demonstrated strong to almost perfect agreement. Questions on the number of indoor (κ = 0.86) and outdoor (κ = 0.75) falls demonstrated moderate to strong agreement, though questions related to the number of indoor (κ = 0.47) and outdoor (κ = 0.56) near-falls demonstrated weak agreement. Moderate to strong agreement scores were observed for the most recent fall and near-fall in terms of the direction (indoor fall κ = 0.80; outdoor fall κ = 0.81; near-fall κ = 0.54), activity (indoor fall κ = 0.70; outdoor fall κ = 0.82; near-fall κ = 0.65) and cause (indoor fall κ = 0.75; outdoor fall κ = 0.62; near-fall κ = 0.56). CONCLUSIONS: The new PDF-Q developed in this study was found to be reliable for capturing the circumstances and consequences of recent falls and near-falls in older adults with PD.

Physical activity accumulation along the intensity spectrum differs between children and adults.

PURPOSE: Detailed exploration of physical activity accumulation with fine grading along the intensity spectrum has indicated the potential pragmatic utility of such an approach. However, it is currently unclear what sorts of accumulation patterns along particular intensity bands are found in the children and adult populations. Therefore, we conducted a comparison of activity accumulation in specific intensity bands between four distinct populations: children, adults with sedentary lifestyles, habitual joggers, habitual marathon runners. METHODS: Free-living waist-worn accelerometry records from 28 children aged 7 to 11, and 61 adults aged 25 to 35 were analysed. Activity intensity was evaluated in 5 s non-overlapping epochs as mean amplitude deviation (MAD) and normalised to acceleration intensities corresponding to walking at 3 metabolic equivalents of a task (METs). Adult data were normalised to 0.091 g MAD based on literature, and data from children to 0.170 g MAD based on laboratory experimentation. The normalised epoch values were divided into 100 intensity gradations. RESULTS: Children accumulated more activity in 0.74 to 1.58 normalised acceleration intensities (all p < 0.005) compared to adults. Adult joggers/runners accumulated more activity in normalised acceleration intensities from 7.1 to 11.1 compared to the other groups (p < 0.008). CONCLUSION: The primary bulk of children's free-living activities are of relatively low intensity not likely to provoke cardiometabolic improvement. These sorts of explorations could be used in informing intervention development aiming at optimising healthy development. Evidence is mounting to justify randomised controlled trials based on intervention targets identified based on exploring the intensity spectrum.

Use of walking modifications, perceived walking difficulty and changes in outdoor mobility among community-dwelling older people during COVID-19 restrictions.

BACKGROUND: Outdoor mobility enables participation in essential out-of-home activities in old age. AIM: To compare changes in different aspects of outdoor mobility during COVID-19 restrictions versus two years before according to self-reported walking. METHODS: Community-dwelling participants of AGNES study (2017-2018, initial age 75-85) responded to AGNES-COVID-19 postal survey in spring 2020 (N = 809). Life-space mobility, autonomy in participation outdoors, and self-reported physical activity were assessed at both time points and differences according to self-reported walking modifications and difficulty vs. intact walking at baseline were analyzed. RESULTS: Life-space mobility and autonomy in participation outdoors had declined (mean changes -11.4, SD 21.3; and 6.7, SD 5.3, respectively), whereas physical activity had increased (5.5 min/day, SD 25.1) at follow-up. Participants perceiving walking difficulty reported the poorest baseline outdoor mobility, a steeper decline in life-space mobility (p = 0.001), a smaller increase in physical activity (p < 0.001), and a smaller decline in autonomy in participation outdoors (p = 0.017) than those with intact walking. Those with walking modifications also reported lower baseline life-space mobility and physical activity, a steeper decline in life-space mobility and a smaller increase in physical activity those with intact walking (p < 0.001 for both). DISCUSSION: Participants reporting walking modifications remained the intermediate group in outdoor mobility over time, whereas those with walking difficulty showed the steepest decline in outdoor mobility and hence potential risk for accelerated further functional decline. CONCLUSION: Interventions should target older people perceiving walking difficulty, as they may be at the risk for becoming homebound when environmental facilitators for outdoor mobility are removed.

Associations of age, body size, and maturation with physical activity intensity in different laboratory tasks in children.

We investigated the associations of age, sex, body size, body composition, and maturity with measures of physical activity (PA) intensity in children. PA intensity was assessed using VO2 as % of VO2reserve or VO2 at ventilatory threshold (VT), muscle activity measured by textile electromyography, mean amplitude deviation (MAD) measured by accelerometry, and metabolic equivalent of task (MET) during laboratory activities.Age, stature, and muscle mass were inversely associated with VO2 as % of VO2reserve and % of VT, during walking or running on a treadmill for 4, 6, and 8 km/h (Spearman r = -0.645 to -0.358). Age was inversely associated with MAD during walking on treadmill for 4 km/h (r = -0.541) and positively associated with MAD during running on a treadmill for 8 km/h, playing hopscotch, and during self-paced running (r = 0.368 to 0.478). Fat mass was positively associated with VO2 as % of VO2reserve and VO2 as % of VO2 at VT and waist circumference was positively associated with VO2 as a % of VO2reserve and muscle activity during stair climbing (r = 0.416 to 0.519).Fixed accelerometry cut-offs used to define PA intensities should be adjusted for age, sex, body size, and body composition.

The skeletal maturity of Australian children aged 10-13 years in 2016.

Skeletal maturity can be used as a biological indicator of the tempo of growth in children and adolescents. We present a description of skeletal maturity from a cohort of white Australian children and describe variation in skeletal maturity based on child age. Participants (n = 71; age 10.5-13.9 years) were recruited from the 'Healthy, Active Preschool & Primary Years (HAPPY)' study. Left hand-wrist radiographs were used to determine skeletal maturity using the Tanner-Whitehouse III (TW3) RUS technique. In boys, the mean skeletal maturity offset (bone age - chronological age) was -0.12 ± 0.19 years and 57.9% had delayed skeletal maturity compared to chronological age. Among those with delayed skeletal maturity, the average delay was 0.99 years (range 0.02-2.54 years). In girls, skeletal age was advanced, on average, compared to chronological age by 0.32 ± 0.20 years. Among the 39.4% of girls with delayed skeletal maturity, the average delay was 0.48 years (range: 0.01-2.28). Four children in the sample exhibited a delay in skeletal maturity greater than 2 years. In the context of secular trends towards advanced skeletal maturity observed globally, delayed skeletal maturation in this white, economically privileged cohort are surprising and warrant further exploration.

Day-to-Day Variability and Year-to-Year Reproducibility of Accelerometer-Measured Free-Living Sit-to-Stand Transitions Volume and Intensity among Community-Dwelling Older Adults.

(1) Background: The purpose of this study was to evaluate the day-to-day variability and year-to-year reproducibility of an accelerometer-based algorithm for sit-to-stand (STS) transitions in a free-living environment among community-dwelling older adults. (2) Methods: Free-living thigh-worn accelerometry was recorded for three to seven days in 86 (women n = 55) community-dwelling older adults, on two occasions separated by one year, to evaluate the long-term consistency of free-living behavior. (3) Results: Year-to-year intraclass correlation coefficients (ICC) for the number of STS transitions were 0.79 (95% confidence interval, 0.70-0.86, p < 0.001), for mean angular velocity-0.81 (95% ci, 0.72-0.87, p < 0.001), and maximal angular velocity-0.73 (95% ci, 0.61-0.82, p < 0.001), respectively. Day-to-day ICCs were 0.63-0.72 for number of STS transitions (95% ci, 0.49-0.81, p < 0.001) and for mean angular velocity-0.75-0.80 (95% ci, 0.64-0.87, p < 0.001). Minimum detectable change (MDC) was 20.1 transitions/day for volume, 9.7°/s for mean intensity, and 31.7°/s for maximal intensity. (4) Conclusions: The volume and intensity of STS transitions monitored by a thigh-worn accelerometer and a sit-to-stand transitions algorithm are reproducible from day to day and year to year. The accelerometer can be used to reliably study STS transitions in free-living environments, which could add value to identifying individuals at increased risk for functional disability.

Associations Between Accelerometer-Based Free-Living Walking and Self-Reported Walking Capability Among Community-Dwelling Older People.

The authors examined whether accelerometer-based free-living walking differs between those reporting walking modifications or perceiving walking difficulty versus those with no difficulty. Community-dwelling 75-, 80-, or 85-year-old people (N = 479) wore accelerometers continuously for 3-7 days, and reported whether they perceived no difficulties, used walking modifications, or perceived difficulties walking 2 km. Daily walking minutes, walking bouts, walking bout intensity and duration, and activity fragmentation were calculated from accelerometer recordings, and cut points for increased risk for perceiving walking difficulties were calculated using receiver operating characteristic analysis. The authors' analyses showed that accumulating ≤83.1 daily walking minutes and walking bouts duration ≤47.8 s increased the likelihood of reporting walking modifications and difficulties. Accumulating walking bouts ≤99.4 per day, having walking bouts ≤0.119 g intensity, and ≥0.257 active to sedentary transition probability fragmented activity pattern were associated only with perceiving walking difficulties. The findings suggest that older people's accelerometer-based free-living walking reflects their self-reported walking capability.

Biological basis of bone strength: anatomy, physiology and measurement.

Understanding how bones are innately designed, robustly developed and delicately maintained through intricate anatomical features and physiological processes across the lifespan is vital to inform our assessment of normal bone health, and essential to aid our interpretation of adverse clinical outcomes affecting bone through primary or secondary causes. Accordingly this review serves to introduce new researchers and clinicians engaging with bone and mineral metabolism, and provide a contemporary update for established researchers or clinicians. Specifically, we describe the mechanical and non-mechanical functions of the skeleton; its multidimensional and hierarchical anatomy (macroscopic, microscopic, organic, inorganic, woven and lamellar features); its cellular and hormonal physiology (deterministic and homeostatic processes that govern and regulate bone); and processes of mechanotransduction, modelling, remodelling and degradation that underpin bone adaptation or maladaptation. In addition, we also explore commonly used methods for measuring bone metabolic activity or material features (imaging or biochemical markers) together with their limitations.