Using Activity Monitors to Measure Physical Activity in Free-Living Conditions

Abstract

Physical activity is a broad term used to define “any bodily movement produced by skeletal muscles that results in energy expenditure.”1 A physically active lifestyle is associated with a decreased risk for a variety of chronic diseases and health conditions such as cardiovascular disease,2–5 hypertension,6–8 diabetes mellitus,9–12 certain cancers,13–15 depression,16–18 obesity,19, 20 cerebrovascular disease, and premature death.21 The Surgeon General recommends 30 minutes for adults or 60 minutes for children of moderate-intensity activity on most, if not all, days of the week to be physically active and achieve a health benefit.21 The Surgeon General’s recommendation is comparable to expending approximately 150 kcal of energy per day21 for an otherwise healthy individual whose principal mode of activity is walking. Two studies in Japan22, 23 and the popular press have promoted a pedometer-based target of 10,000 steps per day as a way for adults to meet the national physical activity guidelines. Research is ongoing, however, to determine whether this guideline is appropriate for all populations.24–26 According to the Centers for Disease Control and Prevention, more than 25% of US adults do not engage in any leisure-time physical activity, and 60% do not achieve the Surgeon General’s physical activity recommendations.21, 27, 28 Women,29, 30 older adults,31–36 racial and ethnic minority populations, and people with physical disabilities27 are most likely to be inactive.37 The US Department of Health and Human Services has set a national health objective for 2010 to reduce the prevalence of no leisure time activity from more than 25% to 20% of US adults.37 The assessment of physical activity is essential to: (1) determine …