The movement started in San Francisco, when Gary Wolf and Kevin Kelly founded the website in 2007. Now there are groups in more than 20 countries.
"Self-trackers report about their experiences at these meetings. It also gives companies the chance to present new products and get feedback from users," explains Florian Schumacher, who represents the network in Germany.
Kalwies, 30, from Hamburg, is a passionate data gatherer, following the motto: "What gets measured, gets improved."
Doing so lets him be more aware of details like weight, body fat, sleep times and blood sugar.
The new technology makes it easier to gather data and document it.
He measures his sleep with Zeo Sleep Manager.
"This tool measures the quality of sleep and shows how often and when sleep is interrupted and how long the deep sleep phase lasted," he explains.
It means using a headband with sensors and an iOS app.
Kalwies also uses a wi-fi scale with its own app to measure his weight and body fat. Data is automatically sent to a computer or smartphone. Another favourite app is the free program RunKeeper, which measures how quickly a person runs and how many calories are burnt in the process.
Self-trackers can use the online platform www.myvitali.com to assess the data they've gathered with technical aids like pulse trackers, blood pressure monitors, apps and blood sugar gauges.
Registration is free.
There is a difference between actual health apps and simple lifestyle programs. If an app actually helps recognise, prevent or monitor a disease, it can be regarded as a medical product in some countries, which means it has to be approved by authorities and get certified.
"Manufacturers can't decide for themselves how it's categorised," says Beatrix Reiss of Germany's Competence Centre for Telematics in Health Care.
Many prefer not to have their products labelled for medical use, as it gets them out of the certification process and lets them off the hook for eventual damages.
Of course, that can lead to the risk of using an app prone to providing false data. Users should be careful not to place too much blind trust in the makers of apps.
"Data is the currency of the social web," warns Reiss. "Users should be careful with handing over health data and check up on what the manufacturer does with it."
However, her group is generally positive about the self-tracking trend. One positive is the ability to use the data to help doctors make better diagnoses.
"The apps give people the option to learn more about themselves and to motivate themselves with play to reach a set goal,'' she said, noting that there also needs to be limits.
"The danger is that a self-tracker begins to only identify himself by the numbers."
- DPA
