Analysis and interpretation of accelerometry data in older adults: The LIFE study

Background. Accelerometry has become the gold standard for evaluating physical activity in the health sciences. An important feature of using this technology is the cutpoint for determining moderate to vigorous physical activity (MVPA) because this is a key component of exercise prescription. This article focused on evaluating what cutpoint is appropriate for use with older adults 70-89 years who are physically compromised. Methods. The analyses are based on data collected from the Lifestyle Interventions and Independence for Elders (LIFE) study. Accelerometry data were collected during a 40-minute, overground, walking exercise session in a subset of participants at four sites; we also used 1-week baseline and 6-month accelerometry data collected in the main trial. Results. There was extreme variability in median counts per minute (CPM) achieved during a controlled bout of exercise (n = 140; median = 1,220 CPM (25th, 75th percentile = 715, 1,930 CPM). An equation combining age, age2, and 400 m gait speed explained 61% of the variance in CPM achieved during this session. When applied to the LIFE accelerometry data (n = 1,448), the use of an individually tailored cutpoint based on this equation resulted in markedly different patterns of MVPA as compared with using standard fixed cutpoints. Conclusions. The findings of this study have important implications for the use and interpretations of accelerometry data and in the design/ delivery of physical activity interventions with older adults.