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The measuring instrument, activity intensity being measure, the population being measured, mobility limitations, individual behavior and health status -- these all are considerations when measuring the physical activity of persons with chronic and disabling conditions. What is known for sure are the benefits of physical activity. That's why measuring the type, intensity, frequency, and duration of physical activity is needed to determine how well an individual or program is progressing.
Knowing exactly what is being measured is the first step in measuring. For example, exercise, fitness, and physical activity are not the same but do influence each other. Each offers its own measuring criteria. Physical activity, for instance, can be measured by type, frequency, intensity, activity duration, long-term patterns of activity, or distance covered.
Understanding the population being measured for physical activity also is crucial to accurate measurement. For instance, people with disabilities, in general, have lower levels of activity, move differently, take multiple medications, may use assistive devices, may lack fine motor control, or may have thought processing difficulties as compared to the general population. And, attention has to be given to heart monitoring as an activity measurement in certain populations such as people with multiple sclerosis or spinal cord injury who have autonomic nervous system considerations that limit heart rate response to exercise.
Walking, often used to represent a person's overall activity level, has to be tailored for certain populations. For instance, some people with traumatic brain injuries may move slower, and standard pedometers don't work accurately for people of short stature or those who have shuffling gaits. Dependence on walking as a way to measure activity, too, suggests that people who use wheelchairs aren't active and discounts the movement of the upper body, which can be measured by wrist actigraphs.
In 1985, R.E. Laporte, H.J. Montoye, and C.J. Caspersen identified more than 30 ways to measure physical activity. They said there wasn't any method that could measure what it intended to measure, consistently give the same results under the same conditions, ensure accuracy, and be practical for everyone.
Examples of these measures include:
Doubly labeled water. This expensive measure requiring special equipment and trained personal calculates total energy use over one to two weeks. A person drinks a certain amount of water containing isotopes of hydrogen and oxygen that is lost over time because of CO2 production measured in urine tests.
Direct and indirect calorimetry. Used to measure the energy cost of activity over short periods, this measure looks at heat loss from the body (direct) that is measured in a self-contained chamber and expired gases (indirect) detected in face masks and portable gas analyzers.
Heart rate monitors. Best for moderate to vigorous activity, this measurement tool can have varying accuracy.
Pedometers. Inexpensive, these measuring tools that count how many steps are taken aren't sensitive to slow or abnormal giants.
Accelerometers. Becoming more affordable, these activity counts mounted on the waist, hip, back, or wrists are sensitive to low levels of activity and integrate frequency, intensity, and duration of movement.
Self-report. Individuals keep a record of their activities, which can be a burden. People also often credit themselves for more activity than they actually do.
Warms suggested using multiple methods of measurement to eliminate measurement error. It may be effective, for instance, to combine an accelerometer, a questionnaire, and an indicator of fitness such as a six-minute walks to examine the amount of activity, the regularity of activity, and the activity benefits.
"Selection of appropriate sensitive, valid, and reliable indicators of physical activity will not guarantee program effectiveness, but it will provide better indications of the actual physical activity dose required to enhance health and fitness in the PWD [person with a disability]." (p. 86S)
At the time of this study, Catherine Warms could be contacted at the Department of Biobehavioral Nursing and Health Systems, School of Nursing, University of Washington, Seattle, WA 98195, cwarms@u.washington.edu #2157
Warms, C. (2006). Physical activity measurement in persons with chronic and disabling conditions: Methods, Strategies, and Issues. Family Community Health 29(18), 78S-88S.
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