Background: Physical activity is important in obesity, metabolic and cardiovascular diseases and cancer prevention. Several cell phone platforms integrate an accelerometer onto the motherboard. We wrote a software application to access the on board accelerometer from the iPhone (Apple Computer, Cupertino, CA) to measure and quantify physical activity. Here we tested the validity of the cell phone accelerometer to assess physical activity in a controlled laboratory setting.
Methods: 31 subjects wore the cell phone along with the validated Physical Activity Monitoring System (PAMS) with different body postures and during graded walking at 7 velocities. Energy expenditure was measured using indirect calorimetry. Data were also collected from 7346 users who downloaded the "Walk n’ Play" application from the internet.
Results: In all the 31 subjects, the cell phone accelerometer distinguished sedentary and walking activity reliably even with mph increments in walking and was accurate and precise compared to the PAMS, with an intra-class correlation coefficient (r2> 0.98). The cell phone accelerometer showed excellent sequential increases with increased in walking velocity and energy expenditure (r2>0.9). The data from the 7346 free-living people demonstrated that most daily activity detected with the cell phone accelerometer occurs in the low intensity.
Conclusions: An accelerometer embedded into a cell phone was shown to be accurate and reliable in measuring and quantifying physical activity in the laboratory setting. Before a comprehensive integrated physical activity promoting and weight loss platform can be deployed, free-living evaluation is necessary.