Physical activity can be defined as a bodily movement requiring energy expenditure via skeletal muscle contractions (The American College of Sports Medicine, 2000). Therefore, measuring physical activity is difficult within itself as it is not a quantifiable measurement. However, the importance of measuring physical activity is significant as it can predict the onset, or can be implemented diagnostically, for medical conditions e.g. cardiovascular disease, obesity, hypertension and many other health outcomes.
Measuring physical activity can be controversial with regards to accuracy and can be determined by several methods such as physical activity logs (PA Logs), pedometers, heart rate monitors, accelerometry, Borg’s rate of exertion, doubly labelled water (DLW), rate of perceived exertion (RPE) and seven day retrospective physical activity recall questionnaires (Leenders 2001). Each method characterise advantages and disadvantages which are later discussed.
It is useful to question the efficiency of the methods previously mentioned as it is of great interest to professionals such as exercise referral practitioners, athletes etc to measure physical activity and to be aware of which methods are most beneficial.
Three methods were selected and carried out in order to investigate their accuracy with respect to measuring physical activity (PA). The chosen methods were pedometers, PA Logs and heart rate monitors. The female participant female, (aged 20) then applied the three methods simultaneously for the duration of twelve hours fifty five minutes. In order to implement the methods the participant attached the heart rate monitor (chest strap) just below the chest but above the waist, and the receiving module (watch) on the left wrist (so that it was in closer proximity to the heart). The pedometers were then attached by the participant by clipping the small electronic device to the waistband of their trousers in order to be within close proximity of the hip. Once the twelve hours fifty five minutes had been completed, the participant was permitted removal of the equipment and to continue with their daily routines.
The data collected from the heart rate monitor and pedometer was then uploaded to a computer system called Polar Precision Performance so that the information could be analysed.
The methods chosen were selected for a number of reasons. Heart rate monitors are known to be widely used (Achten, 2003). Although O’Toole (1998) agrees with this consensus, it is also questioned due to little documentation about their use. This was a good basis to employ the use of heart rate monitors in this experiment as any implications that may have occurred could be experienced first hand. Not only was the contentiousness that surrounds the use of heart rate monitors the rationale for selecting this method but also the accessibility of the equipment and convenience for the participant (i.e. discreetly worn by participant, not too uncomfortable etc).
The Polar heart rate monitor put into practise, for each given QRS complex, transmitted an electronic signal from a chest strap which incorporated dry electrodes, to a receiving module (in this case a watch positioned on the left wrist of the participants) that presented the resultant heart rate (Joglar, 1999).
Leenders (2001) explains that pedometers are small electronic devices which can be discreetly located on the clothing near the hip of the participant. They operate via vertical accelerations of the hip causing the horizontal, spring-suspended lever arms to move up and down, thus making electrical contact and recording the step. Therefore, due to the simplicity of the procedure, ability to be discreetly carried out and convenience for the participant, pedometers were the second method to be adopted to measure PA.
Finally, PA Logs were employed due to their cheap, convenient and insightful characteristics. PA Logs, as previously mentioned, require the participants to record all ambulation throughout the duration of the experiment. According to Ferrari (2007) PA Logs are the most feasible and accurate method.
Unlike PA Logs, heart rate monitors and pedometers, doubly labelled water (DLW) is a more complex procedure involving administering isotopes via injections or orally to measure carbon dioxide production. Additionally DLW is more time consuming as measurements are required at regular intervals and are more expensive to administer (Schoeller, 2007).
Seven day retrospective physical activity recall questionnaires (or in this case, one day retrospective physical activity recall questionnaires) were not selected. Despite the PAR questionnaires illustrating a depth to the information given, (including personal perception) it was more time efficient for the participants as well as the researcher to adopt the three methods that were decided upon. In contrast, the Borg’s scale of perceived exertion was eliminated from the study as it is too vague a measurement. Despite pedometers also producing potentially vague data, it was decided to question the efficiency of pedometers as it is a quantifiable measurement and classes as raw data where as this is not applicable to RPE.
Accelerometry is a method that was decided against due to the complex structure of the procedure. It is used to measure physical activity with regards to acceleration and can provide an insight of energy expenditure. There are two types of accelerometers, triaxial (Tritrac-R3D) and uniaxial (Computer Science Applications [CSA] model 7164), measuring accelerations in three planes, anterior-posterior (x), medio-lateral (y) and vertical (z) or soley one direction (vertical, z) respectively (Leenders, 2000).
Triaxial accelerometers function via summarising the x, y and z acceleration as a vector magnitude (Vmag) and is calculated as the square-root of the sum of the x, y and z accelerations (squared). Once Vmag has been calculated, physical activity related energy expenditure (PAEE) can then be calculated via the manufacturer’s proprietary equations by taking the participant’s body mass into account. Basal metabolic rate (BMR) then needs to be summed in order to work out total daily energy expenditure (TDEE). BMR takes the participants age, height, weight and gender into account by using an equation.