Australasian Science: Australia's authority on science since 1938

Quantify Thyself

By Tim Olds

Fitness devices that track our daily activity are now common, but do they live up to the hype?

Were there a modern version of the Temple of Apollo at Delphi, we might find inscribed on the stones there the aphorism

“Quantify thyself”. The Quantified Self movement enjoins us to enlighten ourselves by wearing unobtrusive electronic sensors to track our movements, moods, diet and environment 24/7. Think FitBit, Fuelband, Shine, ActiHeart, Striiv, Zip, Actiwatch, Lumos, Vivofit, Jawbone, Polar, Digiwalker, SenseWear, Actical, GeneActiv, Actigraph, ActivPAL, Pulse … and now the iWatch.

The ideal of the Quantified Self works like this:

  1. strap on your activity tracker;
  2. download your data to the Cloud;
  3. the Cloud analyses and interprets it;
  4. analysed data are fed back to you or your health provider, who …
  5. … advises you on how to change your behaviour to optimise your health; then
  6. repeat.

Some devices claim to be able to measure the amount of exercise you do, how many steps you take, your posture, how well you sleep, how much time you spend sitting down and how many calories you burn. They generally cost between $50 and $250.

Almost all of these devices contain an accelerometer, which measures acceleration of the body part to which the device is connected, plus the acceleration of the whole body (and any vehicle it’s in). Nowadays, most devices use tri-axial accelerometry to measure movement up and down, left and right, back and forwards.

Some devices have other sensors as well. Some measure heart rate (or claim to, as heart rate measured at the wrist is not particularly reliable), near-body temperature and galvanic skin response as a measure of sweat. Some have gyroscopes or inclinometers to determine body position, as well as GPS devices embedded.

More sophisticated analysis uses pattern recognition algorithms to try and guess what the person is doing – are they using a computer or driving? We are currently working on systems that also employ metadata (such as the age and sex of the wearer) combined with use-of-time databases to improve our guesses about what people are doing.

So if you want to get one, which should you get? The most common research-level devices are the Actigraph, GeneActiv and ActivPAL, but they’re expensive and don’t provide any feedback. You need to be an expert to interpret the data. Among commercial devices, the FitBit is emerging as a reliable, valid device.

But let’s not get ahead of ourselves. Very few of the claims of the manufacturers of these devices have been validated. We still have a long way to go, and there are lots of hurdles.

One technical hurdle is battery life. The iWatch, for example, needs to be charged overnight, so it can’t quantify sleep.

Interpretation of data is never straightforward. There are many competing thresholds for physical activity, and they yield wildly discrepant estimates of how much time we have been exercising.

We often don’t even know if the person has just been very inactive or has not been wearing the device at all for hours on end. There are still no generally accepted algorithms for identifying sleep onset and waking, and there are debates about the best place to wear the monitor. Until recently, the hip was in favour, but a very large American survey has now switched to the wrist, which results in better compliance and more options for pattern recognition. Some devices are worn as armbands, or around the neck, or clipped to clothing.

Even with these limitations, there have been great strides in activity identification. We recently demonstrated that wrist-worn accelerometers can tell whether you are drinking a cup of tea or a glass of wine. (There are more frequent sips with tea, and not as wide an arc of arm movement; people tend not to put down their tea cup between sips.)

And as for sudden bursts of activity in the middle of the night, we can tell not only what you are doing and how long you kept it up, but also your preferred position.

All this raises ethical issues. After all, you wouldn’t want just anyone knowing whether you preferred wine or tea, would you?

Professor Tim Olds leads the Health and Use of Time Group at the Sansom Institute for Health Research, University of South Australia.