Measurement of physical activity in obese persons: how and why? A review

Abstract

[Purpose] Overweight and obesity are major risk factors for poor health, especially in children. Reduced physical activity, prompted by a sedentary lifestyle, is a major contributor. Hence, it is important to assess physical activity using standardized methods in public health to identify the risks associated with obesity. There have been no recent reports comparing such modalities for use by clinicians and researchers. In this article, some of these methods for use in the assessment of physical activity are reviewed, and their advantages and disadvantages are described. [Subjects and Methods] Electronic databases including PubMed, Medline, and Google Scholar were searched for literature, using key words Obesity, Physical activity, and Physical Behavior Monitoring. [Results] With advances in technology, various novel methods have been developed to assess physical behavior, but conventional methods are still relevant and easy to administer. [Conclusion] There are various measurement options available. Researchers may choose devices providing more accurate measurements, while clinicians may prefer portability and affordability for patients.

INTRODUCTION

Actions performed by individuals in their daily lives, such as sleeping, walking, exercising, and watching television, are described as physical behavior. Monitoring of such behavior has helped researchers to broaden their perspective about prevention and rehabilitation of patients with various diseases and disorders^{1, 2)}. With advances in technology, various novel methods have been developed to assess physical behavior, but conventional methods are still relevant and easy to administer^3,4,5).

Overweight is a major risk factor for poor health in children⁶⁾, and various studies have reported a significant rise in the incidence and prevalence of obesity in overweight children^7,8,9,10). Overweight children are likely to become overweight adults, with associated cardiovascular and metabolic diseases^11,12,13). Change in physical behavior as a component of lifestyle modification in treatment of obesity has been widely recommended¹⁴⁾, but its role as a risk factor in the development of obesity has not been well documented. Lack of physical activity may be a cause of overweight, and may be associated with a sedentary lifestyle, including increased duration of TV watching and internet use¹⁵⁾. Time spent while using such media comprises sedentary activity, and is negatively correlated with physical activity scores and positively correlated with body composition indices, which lead to overweight¹⁶⁾. Sedentary behavior is an independent risk factor for development of overweight and associated risk factors that may differ with gender¹⁷⁾. Although it is a relative term, more time spent in sedentary activities does not necessarily mean less physical activity¹⁸⁾.

Besides genetics, diet, and hormonal levels, the level of physical activity is also a major determinant of normal growth, development, and maturation in children^{19, 20)}. Physical activity also lowers the genetic predisposition to increased body mass index (BMI) that in turn leads to obesity^{21, 22)}. Physical activity increases the resistance to physical stressors and protects against mental stress²³⁾. Hence it is important to assess physical activity using standardized measures in public health to identify the risk factors associated with obesity, especially in children^{1, 24)}. Assessment of physical activity can include intensity, frequency, duration, type, or mode²⁵⁾. Appropriate methods for assessment also depend on the setting (indoors or outdoors), and location and reason (leisure, work, etc.) for activity²⁶⁾.

Various subjective and objective methods have been used to measure daily physical activity^{27, 28)}. These include physiological methods such as oxygen consumption and heart rate, and behavioral tools such as questionnaires and interviews.^{27, 29,30,31)}. For better generalizability of data on physical activity, these measures should be reliable, valid, and easy to administer, to meet the needs of global cultural diversity^{4, 10)}. There have been no recent reports comparing such modalities for use by clinicians and researchers³²⁾. Hence, this article reviews some of the methods used to assess physical activity, and describes their advantages and disadvantages. The list of methods presented in this article is inclusive but not exhaustive, and there are no commercial relationships with manufacturers.

SUBJECTS AND METHODS

Databases including PubMed, Medline, and Google Scholar were searched for literature, using the key words Obesity, Physical activity, and Physical Behavior Monitoring. References in retrieved articles were also searched for cross references. The search was limited to articles in English.

RESULTS

After elimination of duplicate papers, relevant papers published in the last 20 years were studied. These included randomized clinical trials, cohort studies, and systematic reviews.

DISCUSSION

In this section, we evaluate physical activity monitoring methods based on type, accuracy, ease of administration, cost, availability, and quality, for use in daily living. The choice of method used to measure physical activity depends on the type, duration, and reason for the physical activity.

Self-reporting methods: These include subjective measures such as 24-hour recall through questionnaires, interviews, and activity diaries³³⁾. These are widely used to assess physical activity, but have advantages and disadvantages^{34, 35)}. Their affordability, adaptability, and ease of use allow them to obtain both qualitative and quantitative data about the level of physical activity for a larger population¹⁰⁾. However, there is a possibility of overestimation^{36, 37)}, with errors in reporting, validation of data, and repeatability of measurement^{38, 39)}. Although various questionnaires are available, their reliability and validity has not been reported^{35, 40)}. Two of the most popular self-reporting methods are the following:

1. The International Physical Activity Questionnaire (IPAQ) is a popular method of measuring physical activity patterns, and can be administered by telephone interview or self-reporting^{2, 35)}. It can measure the nature of physical activity with a minimum duration of 10 minutes at moderate and vigorous intensity levels³⁵⁾. Various studies have demonstrated its reliability and validity, mostly in developed countries⁴¹⁾. Literacy rate, cultural differences, and climate induce differences in the nature of physical activity in developing and developed countries⁴²⁾, that lead to the need for a more globally acceptable questionnaire.

2. The Global Physical Activity Questionnaire (GPAQ) was developed by the World Health Organization in 2002³⁾. It was based on the IPAQ and consists of 19 questions regarding physical activity under domains of work, transport, and discretionary activities⁴²⁾. Studies have indicated that GPAQ is a suitable, reliable, and widely accepted instrument for physical activity assessment in large populations across different cultures¹⁰⁾.

Immaturity, difficulty in recall, and variable patterns of activity in children²⁵⁾, and general decline in the elderly make self-reported physical activity assessment different in these groups⁴³⁾. Methods of self-reporting cannot provide accurate data in these cases⁴⁴⁾. The Children’s Physical Activity Questionnaire and the Youth Physical Activity Questionnaire were devised for younger age groups, but studies were unable to establish accurate estimates of the time spent in moderate and vigorous intensity physical activity and energy expenditure⁴⁵⁾. For the elderly, the Modified Baecke Questionnaire and the Yale Physical Activity Survey have been discussed in the literature, but individual cognitive levels and a wide range of activity patterns are expected to affect the data⁴⁶⁾.

Pedometry: Pedometers are motion sensors that are typically worn on the waist to count the number of steps during locomotion⁴⁷⁾. They are designed to capture vertical motion of the hip joint with movement⁴⁸⁾. Objectivity, small size, easy availability, and low cost make pedometers popular among physicians who prescribe them for patients for self-monitoring and providing feedback on daily physical activity^{49, 50)}. Unlike self-reporting methods, these give a better picture of physical activity by measuring footsteps³⁷⁾. However, they cannot capture activities that do not involve displacement, like lifting weights, isometric exercises, or activities that involve variable speed or upper body motion only, such as cycling or swimming⁴⁷⁾, and cannot measure temporal variables of movement, distance traveled, and intensity and duration of physical activity^{51, 52)}. Various popular smart phones are also equipped with this application.

Various studies that compare different available models on the market report wide variation in their measurements^{53, 54)}, which must be considered in research⁵⁵⁾. However, there are also studies that report these methods to be valid for physical activity measurement in comparison to accelerometers, observation, and self-reporting methods^{56, 57)}.

Accelerometry: Accelerometers are the most objective method for measurement of physical activity, especially in outdoor settings³³⁾. These devices use various technologies such as piezoelectric effects to measure acceleration along a movement axis⁵⁸⁾. Depending on the model, they can be worn on the wrist, waist, or foot; they have a comparatively lower cost and are easy to use⁵⁹⁾. Newer variants also have the capacity to measure acceleration in vertical, horizontal, and mediolateral planes^{60, 61)}. In addition to providing feedback, they can also measure temporal parameters and allow data transfer for further calculations and later use⁶²⁾. Sedentary activity is classified as <100 counts/min, while <1,952 counts/min, 1,952–5,724 counts/min, and >5,724 counts/min are regarded as light, moderate, and vigorous physical activities, respectively⁶³⁾. These values are different for a younger age group⁶⁴⁾. These devices must be worn continuously throughout the recoding period⁴²⁾.

Despite being widely used, accelerometers lack the capacity to measure physical activity that involves only upper body movements, such as the vertical motion component during cycling, and activity while carrying loads, and they underestimate recording while walking on inclined surfaces^{47, 65)}. Studies have shown differences in recording within and between models⁶⁶⁾, and in use in the pediatric age group⁶⁷⁾.

Heart Rate monitors: Heart rate is used in exercise prescriptions as it increases linearly with moderate to strenuous physical activity⁶⁸⁾. It can also be used to calculate energy expenditure⁶⁹⁾. Small size and low cost of monitors make these popular for measurement of habitual physical activity with or without displacement⁴⁷⁾. Commonly available heart rate monitors are attached to the chest with a strap or electrodes, and are not always feasible for use, as they are difficult to mount without assistance, and because electrode placement may leave irritation and marks on the skin⁷⁰⁾.

Although these devices are shown to have high reproducibility⁷¹⁾, there are reports that they are less accurate during low intensity physical activity and in cases where the heart rate is affected by factors other than activity, e.g., high temperature, humidity, or stress⁷²⁾. Absolute heart rate values and heart rate indices, including activity heart rate, are reportedly derived from actual readings to obtain more meaningful values and overcome such limitations⁷³⁾. Heart rate monitors have also been shown to interfere with other electronic devices.

Combination devices: Each of the methods mentioned above have their own advantages and disadvantages. To make the most out of the data recorded and recent advances in technology, two parameters can be combined to obtain a better outcome³³⁾. It was first reported in 1988 that the combination of heart rate and motion analysis can be more meaningful than the individual measurements⁷⁴⁾. Since then, various studies have found that such devices can improve accuracy of measurement during activities of daily living⁷⁵⁾. These may combine heart rate and movement sensors, movement and temperature sensors, or multiple sensors to record motion of different body segments²⁵⁾.

In a situation in which low physical activity takes place at high speed (e.g., riding in a car), use of an accelerometer along with heart rate measurement would provide a more meaningful estimate than either alone⁴⁷⁾. Multi-sensor devices can be complex at times, involving various circuits and wires, and are costlier than currently available devices, making them difficult to use in research involving a large number of subjects²⁵⁾. Although such devices can provide more accurate results, their feasibility, reliability, and validity should be verified before they are more widely used, especially in research²⁵⁾.

In conclusion, physical inactivity often leads to serious health hazards, especially in overweight people. The latest methods are required in research, clinical use, and daily life applications for physical behavior monitoring and tracking of changes in physical activity patterns in overweight and obese patients. There are various options available in the market. Researchers may choose devices providing more accurate measurements, while clinicians may prefer portability and affordability for patients.