BioTrainer™ Activity Monitor - Advanced Information
Measuring Physical Activity; A Comparison of Available Methods:
Increasing evidence points to the need to know more about the health benefits of physical activity, and the effectiveness of activity interventions. A major limiting factor in studying and monitoring physical activity behaviors and the associated health benefits has been the lack of a reliable, valid, and standardized assessment tool (Melanson & Freedson, 1996).
Assessing physical activity is a complex and challenging issue. There are a number of methods to assess physical activity and each has some relative advantages and disadvantages (Tudor-Locke & Myers, 2001). Self-report instruments are the most commonly-used indicators of physical activity. Direct observation techniques have been commonly used to assess activity behavior. (McKenzie, et al, 2000, Elder, et al, 1998, Rowe, et al, 1997, Sallis and McKenzie, 1991).
The most effective tools for measuring physical exercise are various electronic motion-sensing devices that capture details about activity patterns during normal daily life (Welk, Corbin, Dale, 2000). These instruments overcome the limitations of self-report and direct-observation instruments and provide an objective indicator of physical activity. A formidable task for the use of these motion-sensing devices is to provide an uncomplicated method of direct assessment and achievement scoring and reward that is easy to understand and administer.
A number of different electronic devices are available including heart rate monitors, pedometers, and accelerometer-based activity monitors all of which have their own advantages and disadvantages.
The sections below will provide more detail on these devices and lead to a justification for the measurement approach selected for the BioTrainer activity monitor.
Heart Rate Monitors:
Heart rate monitors are popular in many physical exercise programs to teach cardiovascular fitness and to track activity. While heart rate monitors can deliver useful information during specific exercise workouts they are not useful for tracking physical activity patterns under the normal lifestyle activities of daily living and rate can be influenced by nervousness, dehydration, and stress (Welk, Corbin, & Dale, 2000b). They are prone to interference from other electrical equipment (and other monitors) and are inconvenient for participants to wear.
While heart rate monitors can provide a useful indicator during specific bouts of exercise, they are not useful for tracking activity patterns under normal activities of daily living (Welk, Corbin, & Dale, 2000b). Welk’s research also cited another major problem with heart rate monitors is that the more physically-active user may actually have a lower heart rate than their more sedentary counterparts, a variable which could be confounding to the user. Further, heart rate does not typically increase or decrease to a large degree with normal life-style activities, although it does with more strenuous activities. Thus the heart-rate monitor is not sensitive enough to record the more subtle changes in physical activity which is easily accomplished with accelerometers.
Pedometers:
For a number of years, the pedometer (also known as a stepometer or step-counter) has been used successfully to motivate and assess physical activity and increase walking behavior (Todor-Lock, C., 2002). Although pedometers are very cost effective, one of the main flaws in using pedometers however is that they do not record intensity or velocity of movement nor do they have memory storage, restricting their use to measures of total accumulated steps per day.
Limitations of Pedometers:
Despite the appeal and popularity of pedometers, they also have many mechanical and functional limitations. Most pedometers use a simple spring suspended lever arm (sensor) that moves up and down and makes contact with ambulation. An electrical circuit closes with each step and the accumulated step count is displayed digitally on a LCD screen.
The main problem however is that they do not measure the intensity (how hard), duration (how long), or frequency (how often) physical activity occurs (Beighle, Pangrazi, & Vincent, 2001).
In addition, pedometers generally underestimate the number of steps taken during higher intensity activities (Rowlands, Eston, & Ingledew, 1999) and show consistently more errors during slow walking (Bassett et al., 1996). Discrepancies among different models of pedometers can also limit their usefulness (Freedson & Miller, 2000).
Furthermore, pedometers display steps taken over a period of time and are not able to store or recall single-day values over a period of many days. Thus, daily written records must be kept if the pedometer is reset daily.
Pedometers are also not as accurate for people who do a fair amount of bending and/or who have excessive abdominal fat, as the pedometer may move away from the person’s body (Tudor-Locke & Myers, 2001b). Additionally, pedometers cannot distinguish between walking and running (Bassett, 2000) and cannot measure static movements, non-locomotor activities, upper-body exercises and cycling (Beighle, Pangrazi, & Vincent, 2001).
Activity Monitors:
Recent studies and technological advances have shown that frequency, duration, and intensity of physical activity can be objectively measured by wearable acceleration-based activity monitors, and these devices can accurately record body movements.
A variety of commercially-available activity monitors measure complex physical activity patterns, display and store the data, and some designs provide download for PC analysis. These devices are usually small and unobtrusive but differ from pedometers in that they can sample and store detailed information about intensity levels, movements, and physical activity patterns (Kohl et al., 2000).
Uni-axial accelerometers measure accelerations in a single plane, and can be attached to the trunk or limbs, whereas tri-axial accelerometers measure accelerations along three planes; vertical, anterior-posterior, and medio-lateral (Freedson and Miller, 2000). The principal function of accelerometers is that the sensor converts physical movements into electrical signals that are proportional to the muscular force producing motion (Melanson and Freedson, 1996).
They can also be used to estimate caloric burn and energy expenditure (Welk, et al.,2000). The monitors are small, easy to use, and well-suited to assessing physical activity in both children and adults.
These monitors come in many forms and are designed to perform a variety of functions but have been largely used for research applications and can be very expensive (up to $2,000) and out of the price range for the commercial consumer.
BioTrainer Activity Monitor
The BioTrainer activity monitor is a tri-axial accelerometer that very accurately computes and stores both your physical activity and the calories you burn, but is well within the price range for the commercial consumer.
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Literature Cited:
Bassett, D. R. (2000). Validity and reliability issues in objective monitoring of physical activity. Res. Q. Exerc. Sport 71(2): 30-36.
Bassett, D. R., Ainsworth, B.E., Leggett, S.R., Mathien, C.A., Main, J.A., Hunter, D.C., and Duncan, G.E. (1996). Accuracy of five electronic pedometers for measuring distance walked. Med. Sci. Sports Exerc. 28(8): 1071-1077.
Beighle, A., Pangrazi, R. P., & Vincent, S. D. (2001). Pedometers, physical activity, and accountability. JOPERD, 72 (9), 16–19.
Elder, J.P., Broyles, S.L., McKenzie, T.L., Sallis, J.F., Berry, C.C., Davis, T.B., Hoy, P.L., & Nader, P.R. (1998). Direct home observation of the prompting of physical activity in sedentary and active Mexican and Anglo-American Children. Journal od Developmental and Behavioral Pediatrics, 19, 26-30.
Freedson, P. S., and Miller, K. (2000). Objective monitoring of physical activity using motion sensors and heart rate. Res. Q. Exerc. Sport 71(2): 21-29.
Kohl, H. W., Fulton, J.E., and Casperen, C.J. (2000). Assessment of physical activity among children and adolescents: A review and synthesis. Prev. Med. 31: S54-S76.
Mckenzie, T.L., Marshall, S.J., Sallis, J.F., & Conway, T.L. (2000), Leisure-time physical activity in school enviroments: An observational study using SOPLAY. Preventive Medicine, 30, 70-77.
Melanson, E. L., Jr., & Freedson, P. S. (1996). Physical activity assessment: A review of methods. Critical Reviews in Food Science and Nutrition, 36, 385–396.
Rowe, P.J., Schuldheisz, J.M., & van der Mars, H. (1997). Measuring physical activity in physical education: Validation of the SOFIT direct observation Instrument for use with first to eighth grade students. Pediatric Exercise Science. 9(2), 136-149.
Rowlands, A. V., Eston, R. G., & Ingledew, D. K. (1999). Relationship between activity levels, aerobic fitness, and body fat in 8- to 10-yr-old children. Journal of Applied Physiology, 86 (4), 1428–1435.
Sallis, J.F., McKenzie, T.L., Elder, J.L., Galati, T., Berry, C.C., Zive, M., Nader, P.R. (1998). Sex and ethnic differences in children’s physical activity: Discrepancies between self-report and objective measures. Pediatric Exercise Science, 10, 277-284.
Tudor-Locke, C. (2002). Taking steps toward increased physical activity: using pedometers to measure and motivate. Presidents Council on Physical Fitness and Sports Research Digest, 3(17).
Tudor-Locke, C. E., & Myers, A. M. (2001b). Methodological considerations for researchers and practitioners using pedometers to measure physical (ambulatory) activity. Research Quarterly for Exercise and Sport, 72 (1), 1–12.
Welk, G.J., Blair, S.N., Wood, K.W., Jones. S., and Thompson, R.W. (2000a). A comparative evaluation of three accelerometry-based activity monitors. Medicine and Science in Sports and Exercise, 32(9), S489-S497.
Welk, G. J., and Corbin, C.B., and Dale, D. (2000b). “Measurement issues in the assessment of physical activity in children.” Res. Q. Exerc. Sport 71(2): 59-73.
Welk, G., Differding, J. A., Thompson, R. W., Blair, S. N., Dziura, J., & Hart, P. (2000c). The utility of the digi-walker step counter to assess daily physical activity patterns. Medicine and Science in Sport and Exercise, 32 (9), S481–S488.
Welk, G.J., Wood, K., Jones, S.L. & Barlow, C.E. (1999). The validity of three different accelerometers for the assessment of lifestyle physical activity. Medicine and Science in Sports and Exercise, 31, 5 (supplement), S142.