Resumen de Role of sedentary and physical activity patterns on frailty syndrome
Background Frailty syndrome is a condition of increased vulnerability related to aging that leads to a number of adverse health outcomes, including disability, falls, hospitalization, and death. Due to the high pre-frailty and frailty prevalence and the world’s population aging, the prevention and reduction of this syndrome is one of the most crucial challenges facing public health authorities. Reducing the levels of sedentary behaviour and increasing physical activity have been recognized to be key strategies for achieving healthy aging. However, there is a lack of evidence regarding the relationship between sedentary behaviour and physical activity with frailty. Therefore, the general aim of this PhD thesis was to study the role that objectively measured sedentary and physical activity patterns specifically plays in frailty.
Methods The present PhD thesis is composed by 7 studies. The systematic review (study 1) was conducted and reported in accordance with the PRISMA statement using PubMed and Web of Science online databases. The participants of the observational studies were taken from the Toledo Study for Healthy Aging (TSHA). For studies 2 and 3, data were collected from wave 2 with a total subsample of 519 participants finally included. For studies 4 and 5, data were collected from wave 2 and 3 with a total subsample of 771 participants with a single assessment point between both waves. Longitudinal studies (studies 6 and 7) were based on both two data collection waves separated by 4-years with 186 subjects with complete data on all exposures and outcomes. Briefly, sedentary patterns and physical activity were measured by accelerometry. Frailty Trait Scale (FTS) was used to determine frailty levels. Age, sex, educational status, income, and marital status were self-reported by the participants and used as confounding variables in the statistical analyses. Moreover, other health-related outcomes such as body mass index, waist-to-hip ratio, number of drugs, functional fitness, comorbidity status, and cognitive function were assessed with standard procedures and also used as confounding variables. Significance levels were set at P<0.05 in all the analyses performed.
Results The systematic review (study 1) evidenced that objectively measured sedentary behaviour was adversely related to physical performance. However, the association between sedentary behaviour and frailty levels or mortality rates remained unclear and warranted further research. In the cross-sectional study 2, we found that sedentary time per day and the proportion of the day spent in sedentary bouts of 10 minutes or more were positively linked to frailty. In contrast, breaks in sedentary time were negatively associated with frailty levels. In the cross-sectional study 3, we observed that replacing sedentary time with moderate-to-vigorous physical activity is associated with positive theoretical effects on the frailty status. In addition, people with comorbidities may also benefit from substituting sedentary time with light physical activity. When participants were classified into four movement patterns derived from the physically active/inactive and low/high sedentary behaviour categories (study 4), it was found that those physically active older adults had better physical function and frailty profiles than those considered physically inactive, even in the presence of high sedentary time. Higher levels of light physical activity relative to sedentary time seemed to confer additional improvements in the frailty profile between those who meet the physical activity recommendations and also for those who do not. In the study 5, we found that moderate-to-vigorous physical activity was a moderator in the relationship between sedentary time and frailty in older adults, offsetting the detrimental effects of sedentary behaviour with 27 min/d of moderate-to-vigorous activity. In longitudinal studies 6 and 7, cross-lagged panel models revealed that the relationship between moderate-to-vigorous physical activity and sedentary behaviour with frailty was unidirectional: initial moderate-to-vigorous physical activity predicted future frailty and baseline frailty was a predictor of sedentary behaviour at follow-up. Conversely, a reciprocal inverse relationship between breaks in sedentary time and frailty was displayed in physically inactive participants, while in active individuals no associations were found.
Conclusions The relationship between objectively measured sedentary patterns and frailty in older adults was identified as a gap in the scientific literature through the systematic review (study 1). In cross-sectional studies, we found that both reducing sedentary time and introducing frequent short periods of activity within sedentary periods were associated with reduced frailty levels (study 2). In addition, we observed that replacing sedentary time with moderate-to-vigorous physical activity could have positive theoretical effects on frailty (study 3). Light physical activity could be proposed as a middle step strategy for those individuals with comorbidities (study 3), besides to confer additional improvements on frailty status in both those who meet and those who do not meet the recommendations of physical activity (study 4). We also observed that engaging in 27 min/day of moderate-to-vigorous physical activity could eliminate the potential negative effects of sedentary behaviour on frailty (study 5). Finally, based on longitudinal data we found that moderate-to-vigorous physical activity predicts future frailty (study 6), and therefore, whenever possible, efforts should be directed towards the promotion of moderate-to-vigorous physical activity in early stages. For those individuals who do not meet with physical activity recommendations, the relationship between breaks in sedentary time with frailty was negative in both directions (study 7), and consequently, breaking-up sedentary time more frequently could be a good strategy to attenuate the burden associated with frailty. Future evidence should move towards experimental studies in order to address the hypotheses derived from this PhD thesis.
