What metrics did companies like Fitbit primarily focus on when popularizing activity monitors around 2007 and 2008?

Steps taken, distance traveled, and basic sleep patterns.

The initial iteration of personal tracking devices that gained commercial momentum in the late 2000s, spearheaded by companies such as Fitbit, were fundamentally focused on external and straightforward metrics. These early consumer-grade activity monitors served primarily to log observable actions like the total count of steps taken, the overall distance traversed, and rudimentary assessments of sleep patterns. This established the practical form factor and demonstrated consumer appetite for continuous personal data collection before the technology was capable of analyzing subtle internal physiological or biochemical responses indicative of stress.