Tracking your Physical Activity
by Tia Dewick in News
As a result of the increasing commercial availability of tracking devices, the number of the population measuring their physical activity levels is on the rise! There are 4 most common forms of tracking devices (pedometer, watch, accelerometer and ActiPal); however, when utilising these devices to measure your physical activity, be sure to consider some of the following strengths of limitations of these devices:
Pedometer
To this day, the pedometer is still the most commonly used tool to measure physical activity in large epidemiological studies. Despite the high popularity of this device, the human movement is only measured uni-axially. What implications does this have? Well, by moving from a sit to standing position (vertical movement), the force required to counteract gravity causes us to burn the most calories to keep our posture in an upright position. Therefore, this vertical axis is the default setting in pedometers. BUT, throughout the day do you only sit to stand? No, I thought so. As we produce movement vertically, front to back and side to side, the pedometer is missing all of this data and so may under-reports our total energy expenditure.
Fitbit/Apple Watch
The most popular used device within the public is of course the contemporary watch devices. Although the proposed benefit of watches detecting upper body movement which the pedometer, accelerometer and ActiPal all fail to measure, small movement of the wrist can be over-reported. For example do you have a busy desk job? Constantly typing away on the keyboard, picking up the phone, rummaging around for your stationary? Well, if you conduct these activities sitting down, the device is going to assume you are burning more calories than you are as the device assumes that you are standing. They have been shown to over-report by up to 45%! So, when basing your calorie intake on your watch calculated energy expenditure, be sure to consider this significant limitation.
Accelerometer
Next up is the accelerometer which is most commonly strapped around your waist like a belt to calculate your movement patterns through movement of the hip. However, this device fails to identify posture (i.e. your hip remains roughly in the same position when both sitting and standing) and so it may under-report your data if you spend a large portion of your day standing still as it may only detect you’re standing if you move about.
ActiPal
The final most popular measurement tool is the ActiPal. The ActiPal utilises a sticky tape-like material to attach itself to your thigh. Therefore, the ActiPal can detect these sit to stand differentiations in posture which could potentially improve its accuracy. Despite this supposed strength of the ActiPal, some postures still remain unclear (i.e. if you sit with your legs crossed or with your feet out straight in front of you). So, if you do not sit in a typically ‘normal’ seated position (i.e. feet and knees together in roughly a right angle position), perhaps your data may be over-reported as it may categorise these abnormal sitting postures as standing.
Accumulation of Physical Activity
Finally, if you think back to our prior physical activity blog which highlights the current physical activity recommendations, these current recommendations indicate that for movement to be categorised within our 150 minutes of moderate to vigorous intensity the exercise needs to be performed in at least ten minute bouts. Therefore, as these devices also detect light intensity exercise and small bouts of activity (as little of one minute depending on the device make and model), perhaps this criteria does not meet the required exercise domains for optimal health gains. Despite these limitations, the current physical activity guidelines are in review as research has found positive health benefits of both light activity and small accumulated bouts. Some time next year the new guidelines should be released so keep checking our blogs to see when they are released to keep up-to-date with self-monitoring your level of physical activity!