Patterns of physical activity accumulation and their association with physical function

Abstract

This thesis investigates the relationship between patterns of physical activity (PA) accumulation and physical function, focusing on midlife populations. It begins with a systematic review of current evidence linking PA with physical function. The review finds that higher levels of PA, regardless of intensity, are generally associated with better physical function. However, significant gaps are identified, including a predominant focus on older adults and reliance on aggregate measures of PA that overlook how PA is accumulated. To address these gaps, novel metrics are employed to describe patterns of how upright and stepping events are accumulated. These include measures of the fragmentation, temporal distribution, and composition of upright, stepping, and sedentary events. These metrics aim to build on traditional aggregate measures of PA time or volume by adding new information about how a given level of activity is accumulated. The thesis then examines how patterns of PA accumulation vary by a range of sociodemographic factors in two population cohorts: the early midlife population of the 1970 British Cohort Study and the older population of The Maastricht Study. Significant variations in activity accumulation are observed based on age, sex, Body Mass Index, self-rated health, disability, occupational activity, and smoking status—variations that are ignored if only aggregate measures are reported. Next, the thesis examines cross-sectional relationships between patterns of PA accumulation and self-reported and objective measures of physical function. Associations between patterns of accumulation and physical function outcomes are observed in both early and later midlife populations, independent of the volume of physical activity. This thesis adds new knowledge by demonstrating that different people may accumulate the same volume of PA in very different patterns, and that these patterns are associated with physical function, independently of aggregate measures of PA volume. This suggests that future research investigating the relationship between PA and health should assess patterns of PA accumulation in addition to the amount of PA people undertake. Such measures are important not only in older adults but also in midlife, when declines in physical function start to occur. If these findings are confirmed in future longitudinal studies, the next revisions of public health guidelines, population surveillance, and intervention studies should reflect this new evidence to optimise health outcomes.