We appreciate the thoughtful commentary by Chastin and colleagues regarding our recent article entitled “Nonlinear Analysis of Ambulatory Activity Patterns in Community-dwelling Older Adults.” (1) We fully agree with their observation that the application of nonlinear analytical tools to accelerometry data is an emerging area of research that shows potential for illuminating the complex nature of physical activity profiles. We also welcome the opportunity to discuss their concerns regarding (a) our application of detrended fluctuation analysis (DFA), entropy rate, and approximate entropy to natural activity data and (b) our narrow focus on stepping activity
