Chronic disease risk factors, including a sedentary lifestyle, may be present even in young children, suggesting that early prevention programmes may be critical to reducing the rates of chronic disease. Accurate assessment of physical activity in children is necessary to identify current levels of activity and to assess the effectiveness of intervention programmes designed to increase physical activity. This article summarises the strengths and limitations of the methods used to evaluate physical activity in children and adolescents. MEDLINE searches and journal article citations were used to locate 59 articles that validated physical activity measurement methods in children and adolescents. Only those methods that were validated against a more stringent measure were included in the review. Based on the definition of physical activity as any bodily movement resulting in energy expenditure (EE), direct observation of the individual's movement should be used as the gold standard for physical activity research. The doubly labelled water technique and indirect calorimetry can also be considered criterion measures for physical activity research, because they measure EE, a physiologic consequence closely associated with physical activity. Devices such as heart rate monitors, pedometers and accelerometers have become increasingly popular as measurement tools for physical activity. These devices reduce the subjectivity inherent in survey methods and can be used with large groups of individuals. Heart rate monitoring is sufficiently valid to use in creating broad physical activity categories (e.g. highly active, somewhat active, sedentary) but lacks the specificity needed to estimate physical activity in individuals. Laboratory and field validations of pedometers and accelerometers yield relatively high correlations using oxygen consumption (r = 0.62 to 0.93) or direct observation (r = 0.80 to 0.97) as criterion measures, although, they may not be able to capture all physical activity. Physical activity has traditionally been measured with surveys and recall instruments. These techniques must be used cautiously in a paediatric population that has difficulty recalling such information. Still, some studies have reported 73.4% to 86.3% agreement between these instruments and direct observation. Future investigations of physical activity instruments should validate the novel instrument against a higher standard. Additional studies are needed to investigate the possibility of improving the accuracy of measurement by combining 2 or more techniques. The accurate measurement of physical activity is critical for determining current levels of physical activity, monitoring compliance with physical activity guidelines, understanding the dose-response relationship between physical activity and health and determining the effectiveness of intervention programmes designed to improve physical activity.

Physical Activity Assessment in Children and Adolescents

The present study describes the development of a triaxial accelerometer (TA) and a portable data processing unit for the assessment of daily physical activity. The TA is composed of three orthogonally mounted uniaxial piezoresistive accelerometers and can be used to register accelerations covering the amplitude and frequency ranges of human body acceleration. Interinstrument and test-retest experiments showed that the offset and the sensitivity of the TA were equal for each measurement direction and remained constant on two measurement days. Transverse sensitivity was significantly different for each measurement direction, but did not influence accelerometer output (<3% of the sensitivity along the main axis). The data unit enables the on-line processing of accelerometer output to a reliable estimator of physical activity over eight-day periods. Preliminary evaluation of the system in 13 male subjects during standardized activities in the laboratory demonstrated a significant relationship between accelerometer output and energy expenditure due to physical activity, the standard reference for physical activity (r=0.89). Shortcomings of the system are its low sensitivity to sedentary activities and the inability to register static exercise. The validity of the system for the assessment of normal daily physical activity and specific activities outside the laboratory should be studied in free-living subjects.

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A triaxial accelerometer and portable data processing unit for the assessment of daily physical activity

Characteristics of physical activity are indicative of one's mobility level, latent chronic diseases and aging process. Accelerometers have been widely accepted as useful and practical sensors for wearable devices to measure and assess physical activity. This paper reviews the development of wearable accelerometry-based motion detectors. The principle of accelerometry measurement, sensor properties and sensor placements are first introduced. Various research using accelerometry-based wearable motion detectors for physical activity monitoring and assessment, including posture and movement classification, estimation of energy expenditure, fall detection and balance control evaluation, are also reviewed. Finally this paper reviews and compares existing commercial products to provide a comprehensive outlook of current development status and possible emerging technologies.

A Review of Accelerometry-Based Wearable Motion Detectors for Physical Activity Monitoring

Eston, Roger G., Ann V. Rowlands, and David K. Ingledew.Validity of heart rate, pedometry, and accelerometry for predicting the energy cost of children’s activities.J. Appl. Physiol. 84(1): 362–371...

Validity of heart rate, pedometry, and accelerometry for predicting the energy cost of children’s activities

Researchers and practitioners require guidelines for using electronic pedometers to objectively quantify physical activity (specifically ambulatory activity) for research and surveillance as well as clinical and program applications. Methodological considerations include choice of metric and length of monitoring frame as well as different data recording and collection procedures. A systematic review of 32 empirical studies suggests we can expect 12,000–16,000 steps/day for 8–10-year-old children (lower for girls than boys); 7,000–13,000 steps/day for relatively healthy, younger adults (lower for women than men); 6,000–8,500 steps/day for healthy older adults; and 3,500–5,500 steps/day for individuals living with disabilities and chronic illnesses. These preliminary recommendations should be modified and refined, as evidence and experience using pedometers accumulates.

Methodological Considerations for Researchers and Practitioners Using Pedometers to Measure Physical (Ambulatory) Activity

The purpose of this study was a critical evaluation of pedometer and actometer for estimating daily physical activity.

The use of pedometer and actometer in studying daily physical activity in man. Part I: reliability of pedometer and actometer.

The validity of the pedometer and actometer for estimating the daily physical activity was evaluated by means of an observation study. The physical activity in a classroom of 11 pupils of a kindergarten was assessed by means of a pedometer, actometer and by observation. Besides this an activity questionnaire was completed by the infant-quide. On basis of the individual observation it is clear that the infant-guide can give valuable information about the activity of the children at school. The results of the pedometer attached to the waist and the actometers attached to the ankle were significantly correlated with the results of the observation method. The wrist actometer showed a smaller but still significant correlation with the other variables. Implications of this findings are discussed in regard toward the physical activity. The pedometer results point out that when the percentage of intense activity is high the pedometer tends to underestimate the level of activity. The actometer results indicate that such a motion recorder gives a reliable estimation of activity in children. The findings are discussed in terms of the practical applications of the actometer in the research of daily physical activity and the physical rehabilitation treatment of certain diseases.

The use of pedometer and actometer in studying daily physical activity in man. Part II: Validity of pedometer and actometer measuring the daily physical activity

This paper provides a brief description of a new 8-register heartbeat integrator for recording the heart rate over a long period (24-h or more) in order to assess daily physical activity in children and adults.

W. H. M. Saris

Papers

The use of pedometer and actometer in studying daily physical activity in man. Part I: reliability of pedometer and actometer.

The use of pedometer and actometer in studying daily physical activity in man. Part II: Validity of pedometer and actometer measuring the daily physical activity

A portable heart rate distribution recorder for studying daily physical activity.