A Comparison of Subjective and Objective Measures of Physical Activity and Fitness in Identifying Associations with Cardiometabolic Risk Factors
Introduction
Population-based studies have typically relied on self-report measures of physical activity, given their low cost, feasibility, and ability to characterize physical activity by frequency, intensity, duration, and type (1). Despite their widespread use, self-reported activity measures may be subject to unreliable recall and bias, may miss most nonstructured activity, and result in large amounts of random error 1, 2, 3. These limitations may substantially attenuate observed associations with health outcomes, potentially leading to erroneous null findings, and make it difficult to characterize dose-response relationships where they exist.
Objective measures of physical activity such as pedometers are becoming more commonly used in large population studies 4, 5. These relatively low-cost instruments are able to capture lower intensity activities, such as walking and incidental activity, which are difficult to accurately quantify using survey methods (3). However, pedometers are unable to distinguish activity intensity which may be an important limitation where the relationship between physical activity and a health outcome is intensity dependent. Other motion sensors, such as accelerometers, have the ability to quantify activity intensity, but their higher cost has largely prohibited their use in population studies.
Rather than measure physical activity directly, some population-based studies have measured different facets of physical fitness, such as cardiorespiratory fitness. While the facets of physical fitness are known to be influenced by genetic factors, they can be objectively measured and are considered to be acceptable surrogate measures of fitness-related physical activity patterns in adults 6, 7, 8.
Despite the growing choice of measurement options, few studies have directly compared the usefulness of a range of both subjective and objective physical activity measures in quantifying associations with health outcomes. Such data are needed to make informed decisions in selecting the most appropriate measure of physical activity for a given health outcome. Toward this end, this study compared associations between physical activity and cardiovascular risk factors across a range of physical activity and fitness measures.
Section snippets
Study Sample
Data for these cross-sectional analyses were collected in the period 2004–2006 from Australian adults (aged 26–36 years) as part of the Childhood Determinants of Adult Health Study, a follow-up of the 1985 Australian Schools Health and Fitness Survey (N = 8,498; age 7–15 years). Details of the 1985 sampling strategies have been described elsewhere (9). At follow-up, 6,840 (80.5%) of the original participants were successfully traced and 5,170 (60.8%) were enrolled and provided data to the
Results
Summary measures of physical activity, fitness, and cardiometabolic health are described in Table 1. The interrelationship between the alternative measures of physical activity and fitness are presented by sex in Table 2. IPAQ total activity was more strongly associated with self-reported sitting time and pedometer steps than with other non-IPAQ measures of physical activity. In men, IPAQ work activity was more strongly associated with objectively measured pedometer steps and self-reported time
Discussion
Results from this study are useful in evaluating several important issues related to the measurement of physical activity in epidemiological studies. One key issue addressed was the comparative strength of associations using subjective versus objective measures of physical activity. Prior studies have consistently reported weaker associations between self-reported physical activity and cardiovascular health outcomes than those observed using objective measures of aerobic fitness (6). A common
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