• Metabolic Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland. Electronic address: charles.matthews2@nih.gov.
• Metabolic Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland; Kinesiology Department, California Polytechnic State University, San Luis Obispo, California.
• Metabolic Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland.
• Biostatistics Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland.
• Behavioral Research Program, Division of Cancer Control and Population Sciences, National Cancer Institute, Bethesda, Maryland.

INTRODUCTION: The goal of this study was to describe differences in time use and energy expenditure associated with exercise, prolonged TV viewing, and work days in a longitudinal study of older adults.

METHODS: Participants were 1,020 adults who completed previous-day recalls that provided a profile of the use of time in sedentary and physical activity. Time use and physical activity energy expenditure were predicted for each type of day (exercise, prolonged TV, work) using linear mixed models, adjusting for age, sex, season of the year, and day of the week. Data were collected in 2012-2013; analysis was completed in 2017.

RESULTS: Exercise days had less sedentary time (-0.37 hours/day) and light activity (-0.29 hours/day), and less household, work, and shopping activities, such that the increase in total physical activity energy expenditure on exercise days (2.83 MET-hours/day) was only about half that expended during exercise (5.98 MET-hours/day). Prolonged TV viewing days had more total sedentary time (0.86 hours/days) and less light (-0.45 hours/day) and moderate-vigorous intensity activity (-0.41 hours/day), and thus lower total physical activity energy expenditure (-2.43 MET-hours/day). Work days had less sleep (-0.91 hours/day) and more total sedentary time (1.32 hours/day).

CONCLUSIONS: Exercise days had more physical activity energy expenditure, but because of reductions in other activities, only about half of the energy expended during exercise was added to total daily physical activity energy expenditure. Prolonged TV viewing days had less physical activity energy expenditure and less moderate-vigorous activity. These findings provide new insights into possible compensation associated with exercise, and suggest a strong link between TV viewing and physical inactivity.