Duration: April – July 2013


Activity measuring devices are cheap and easy to use. These devices among other things are made for counting steps. These activity trackers are made to give users insight into their daily activity pattern and help improve a healthy lifestyle.


The goal of the study is to evaluate the validity of counting steps for the “Fitbit Zip” and the iPhone app “Activity Sensor”.


Twenty participants (12 adult women and 8 adult men) walked 3 bouts of 2 minutes on a treadmill with the speed levels of 3,2 km/h, 4,8 km/h and 6,4 km/h. They were wearing the two measuring devices in their pant pockets. While doing this, their steps were counted manually as a gold standard.


The measured deviation for the Fitbit Zip at all speed levels was less than 2%, whereas the deviation from the gold standard for the iPhone app was measured up to 50% at the slowest speed. The correlations of the Fitbit Zip are excellent for slow and average speed and fair for the highest speed, for which there is also a statistically significant difference found. For the iPhone app the correlation is low for all speed levels, and for average speed there is also a statistically significant difference found.


This study is described in a thesis for the Bachelor in Physiotherapy at the Hanze University of Applied Sciences Groningen.