Measures
Sedentary Behavior
Accelerometer Data Processing
An activPAL accelerometer (Physical Activity Technologies, Glasgow, Scotland) was attached on the midline of participants’ right anterior thigh for seven consecutive days to objectively measure ST. The activPAL is an accelerometer that is known as gold standard for objectively measuring ST since it can distinguish between sitting/lying and standing (Hart et al., 2011). Data were summarized in epochs of 15 seconds and were downloaded and processed using manufacturer proprietary software (activPAL 173 Professional v8.11.6.70). A day was considered invalid if there was limited postural variation (i.e., ≥ 95% of wear time in one activity) or fewer than 10 hours of valid waking wear time (Morris et al., 2019; Winkler et al., 2016). Only participants with four days of valid activPAL data were included in the analysis (Heesch et al., 2018). The ‘Processing PAL’ (Winkler et al., 2016) application was used to manually double-check the algorithms to exclude sleep for the analysis. Therefore, participants were asked to report the times they went to bed and when they got up in the morning in their sleep diary. If there was an incongruence between self-reported and algorithm-derived sleep time, adaptations were made using the ‘Processing PAL’ application based on the self-reported data (Winkler et al., 2016). Likewise, the created Heatmaps from the ‘Processing PAL’ application were used to manually check the algorithm for potentially misclassified invalid days, since the algorithm seems to be less reliable in older adult populations (Winkler et al., 2016).
Total Sedentary Time and Sedentary Accumulation Patterns: Total ST (minutes/day) was extracted from the accelerometer data to maximize comparability with other studies. For identifying SB patterns many measures exist, but consensus about the best indicators is still lacking (Boerema et al., 2020). Alpha (unitless) is one of the most robust measures and is very sensitive to change (Sebastien F. M. Chastin et al., 2015). Alpha is defined as “the cumulative distribution of bout lengths” and represents the frequency distribution of SB bout duration, which follows the power-law probability distribution (Chastin & Granat, 2010; Sebastien F. M. Chastin et al., 2015). Therefore it acts as a measure that captures the diversity of bout lengths during a day (Boerema et al., 2020). Lower values indicate a SB accumulation pattern with more prolonged bouts, whereas higher values represent a more fragmented SB pattern. One disadvantage of using alpha, is that it can be difficult to interpret. Therefore, a second sedentary accumulation pattern measure, usual bout duration (UBD), was calculated. UBD is the median value of the cumulative sedentary bout duration distribution, and is a universal measure to report bout lengths in relation to total ST (Boerema et al., 2020). All three measures: total ST, alpha and UBD, were calculated using Python. The script can be found at OSF [blinded for peer review].
Physical Functioning
During the first home visit, the Short Physical Performance Battery (SPPB) was performed by trained researchers. This test battery consists of three physical performance tests (balance, walking, sit-to-stand) and is a well-established tool to evaluate functional capability (Guralnik et al., 1994). For each test a subscore ranging from 0 to 4 was created. A summary score for physical functioning was obtained by summing the three subscores, resulting in a score ranging from 0 to 12, with higher scores indicating better physical functioning. A detailed summary of the scoring system can be found elsewhere (De Fátima Ribeiro Silva et al., 2021).
Cognitive Functioning
The Cambridge Neuropsychological Test Automated Battery (CANTAB) was performed during the second home visit. This battery focuses on three cognitive domains: (1) working memory and planning, (2) attention and (3) visuospatial memory.
The CANTAB is the most widely published battery for cognitive function, is largely independent of verbal instruction and is a relatively cheap and accessible method to assess cognitive functioning compared to face-to-face assessments (Lenehan et al., 2016; Smith et al., 2013). The CANTAB was performed using an iPad. To make sure participants were familiar with the device and understood all instructions, a familiarization exercise was performed first (motor screening task, MOT). After that, a subset of five tests was performed: reaction time (RTI, attention and psychomotor speed), paired associates learning (PAL, memory), spatial working memory (SWM, executive functions), delayed matching to sampling (DMS, memory) and rapid visual information processing (RVP, attention and psychomotor speed).
First, Z-scores for all outcomes (e.g. reaction time, error percentage) were calculated (one for RTI, two for PAL, SWM and DMS, one for RVP; n = 8). Second, negatively scored outcomes were reversed so that all were positive scores with a higher score indicating better cognitive functioning. Third, for the cognitive tests with multiple outcomes, composite scores were calculated by averaging the Z-scores of all respective outcomes. To calculate overall cognitive functioning of the participants, an average score of all composite scores was calculated (Gheysen et al., 2019).
Mental Health-Related Quality of Life
Mental health-related quality of life (QoL) was derived from the RAND-36 questionnaire, assessed during the first home visit. First, scores for the following subscales for mental health were calculated: vitality, social functioning, emotional role functioning and mental health (Ware, 1994). Second, the sum of these scores was divided by 4, which resulted in the unweighted RAND-36 Mental Composite Summary (MCS). This RAND-36 MCS is a simple, validated way of interpreting the mental health aspect of the RAND-36 (Andersen et al., 2022).
Feelings of Social Isolation
The Patient-Reported Outcome Measurement Information System (PROMIS) short form for social isolation was assessed. Four items concerning feelings of social isolation were asked, with five answer possibilities ranging from ‘never’ to ‘always’. PROMIS item banks and validated short-forms are created to enable researchers to get insight into participants’ symptoms, functioning and health-related quality of life in an efficient, flexible and precise way (Cella et al., 2010). Scoring was done conform the PROMIS scoring system. A sum-score of all items was calculated to represent ‘feelings of social isolation’, which could only be calculated with complete data. From this raw sum-score, a T-score with mean of 50 and standard deviation of 10 was calculated using the score conversion table, which can be found here.
Socio-Demographic, BMI and co-morbidities
Following variables were obtained via a questionnaire during the first home visit: age (years); sex (male or female); weight (kg) and height (cm), of which BMI was calculated; marital status (single, in a relationship, cohabiting/married); living situation (home, service flat, nursing home); and education (no degree, primary education, vocational secondary education, technical secondary education, general secondary education, higher education and university; which was recoded into ‘no higher education’ or ‘higher education’). Also comorbidities (NSHAP Comorbidity Index, measuring burden of chronic diseases and conditions) were assessed by asking “has a medical doctor told you that you have (had) [condition]?” for a list of 15 conditions, with a range from 0 to 21; scoring details can be found in Vasilopoulos et al., 2014.
Statistical Methods
All analysis were executed using RStudio (R version 3.4.1), the script and anonymized data can be found at the OSF page [blinded for peer review]. Descriptive statistics were performed on socio-demographic data, BMI and comorbidities, SB measures and health outcomes.
Latent profile analysis (LPA), performed using the R package ‘tidyLPA’ (Rosenberg et al., 2018), was conducted to identify latent subgroups of older adults. LPA assumes that subjects can be subtyped with varying degrees of probabilities into subgroup categories that have different configural profiles (Collins & Lanza, 2009). This profile membership is considered as an unobserved categorical variable (cfr. latent) and is estimated based on the optimal fitted model. This is a person-centered approach, which focuses on identifying subpopulations of individuals who show various patterns of values for certain variables and outcomes (Muthen & Muthen, 2000). The following steps were executed for the LPA (Bauer J, 2021):
First, possible theoretically-based indicators for the LPA model were selected, being mean ST/day, alpha and UBD (SB accumulation patterns), global cognitive functioning (CANTAB), mental health-related quality-of-life (unweighted RAND-36 MCS), feelings of isolation (PROMIS) and physical functioning (SPPB), and inter-correlation analyses were performed. For the SB measures, UBD seemed to be more correlated to the other indicators compared to mean ST/day and alpha. Since they are all indicators for SB accumulation patterns, mean ST/day and alpha were removed from the model. Furthermore, to uncomplicate interpretation of the LPA results, all negatively scored indicators (i.e., PROMIS and USB) were scored positively. Second, different models with different numbers of latent classes were estimated and compared based on the following fit indices: Bayesian Information Criterium (BIC), sample-size adjusted BIC (SABIC) and Akaike Information Criterion (AIC) (lower values indicate a better model fit to the data), the Bootstrap Likelihood Ratio Test (BLRT) and entropy values (indicates the overall ability of a model to return well-separated profiles, higher value means better fit with one being perfect classification). Hereafter, the target solution was interpreted substantively. Therefore standardized scores were generated for the included variables, and the class-specific means, probability profiles across indicators and class sizes were consulted. After the LPA, one-way ANOVA or non-parametric Kruskal-Wallis analysis were performed to identify whether different profile groups significantly differed from each other in terms of SB and health outcomes.
One-way ANOVA and Chi² analysis were used to compare socio-demographic characteristics with memberships of different profile groups. When observations for certain subgroups were too small to perform a Chi-square (χ²) test, the Fisher’s exact test was performed. Following socio-demographic variables were used: age (continuous), sex (1 = male, 2 = female), education (1 = no higher education; 2 = higher education), living situation (dichotomous: 1 = living at home or service flat; 2 = nursing home), family situation (1 = living alone; 2 = living together with partner). P-values of 0.05 or less were considered statistically significant.