Timmons et al. BMC Public Health 2012, 12:284 http://www.biomedcentral.com/1471-2458/12/284 S T U D Y P R O T O C O L Open Access The health outcomes and physical activity in preschoolers (HOPP) study: rationale and design Brian W Timmons1*, Nicole A Proudfoot1, Maureen J MacDonald2, Steven R Bray2 and John Cairney3 Abstract Background: The early years are the period of growth for which we know the least about the impact of physical activity. In contrast, we know that more than 90 % of school-aged Canadian children, for example, are not meeting physical activity recommendations. Such an activity crisis is a major contributor to recent trends in childhood obesity, to which preschoolers are not immune. The World Health Organization estimated that more than 42 million children under the age of 5 years were overweight world-wide in 2010. If an activity crisis exists during the preschool years, we should also be concerned about its broader impact on health. Unfortunately, the relationship between physical activity and health during the early years is poorly understood. The goal of the Health Outcomes and Physical activity in Preschoolers (HOPP) study is to describe how the prevalence and patterns of physical activity in preschoolers are associated with indices of health. Methods: The HOPP study is a prospective cohort study. We aim to recruit 400 3- to 5-year-old children (equal number of boys and girls) and test them once per year for 3 years. Each annual assessment involves 2 laboratory visits and 7 consecutive days of physical activity monitoring with protocols developed in our pilot work. At visit 1, we assess body composition, aerobic fitness, short-term muscle power, motor skills, and have the parents complete a series of questionnaires related to their child’s physical activity, health-related quality of life and general behaviour. Over 7 consecutive days each child wears an accelerometer on his/her waist to objectively monitor physical activity. The accelerometer is programmed to record movement every 3 s, which is needed to accurately capture the intensity of physical activity. At visit 2, we assess vascular structure and function using ultrasound. To assess the associations between physical activity and health outcomes, our primary analysis will involve mixed-effects models for longitudinal analyses. Discussion: The HOPP study addresses a significant gap in health research and our findings will hold the potential to shape public health policy for active living during the early years. Keywords: Early years, health-related fitness, body composition, cardiovascular, motor skills Background Even though early childhood is a critical period for the de- velopment of active living behaviours, it is the period of growth for which we know the least about the health im- pact of physical activity [1]. In contrast, the health benefits of physical activity for school-aged children are well estab- lished [2,3]. It may be that society has traditionally thought of the early years as a time when very young children are ‘active enough,’ so important questions regarding physical activity and health in this age group have gone unanswered. * Correspondence: timmonbw@mcmaster.ca 1Child Health & Exercise Medicine Program, Department of Pediatrics, McMaster University, 1280 Main Street West, Hamilton, ONL8S 4K1, Canada Full list of author information is available at the end of the article In Canada and around the world, preschoolers are not immune to trends in obesity. Canadian studies estimate the prevalence of obesity among 2- to 5-year-old children to be ~8% [4,5] and ~11% [6], depending on geographical loca- tion, and the World Health Organization estimated that in 2010 more than 42 million children under the age of 5 years were overweight worldwide [7]. One consequence of obesity during the early years may be an acceleration of what has previously been considered adult-onset disease. We know, for example, that signs of atherosclerosis are present in early childhood [8], and reduced vascular function has been identified as part of the atherosclerotic process. There is also evidence that risk of cardiovascular disease later in life can be attributed to health-related fitness levels during © 2012 Timmons et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.