An Inertial footpod is a device used to track running measurements such as speed

Speed

In kinematics, the speed of an object is the magnitude of its velocity ; it is thus a scalar quantity. The average speed of an object in an interval of time is the distance traveled by the object divided by the duration of the interval; the instantaneous speed is the limit of the average speed as...

, distance

Distance

Distance is a numerical description of how far apart objects are. In physics or everyday discussion, distance may refer to a physical length, or an estimation based on other criteria . In mathematics, a distance function or metric is a generalization of the concept of physical distance...

 travelled, pace

Pace

Pace may refer to:*Pace , the speed at which movement occurs*Pace , a unit of length*"Peace" in Italian, sometimes written on a rainbow flag...

, etc., which would generally only be available on treadmill

Treadmill

A treadmill is an exercise machine for running or walking while staying in one place. The word treadmill traditionally refers to a type of mill which was operated by a person or animal treading steps of a wheel to grind grain...

s or with a GPS unit.

This device is usually small and attaches to a runners foot. It uses one or more accelerometers and processes several times a second to compute speed.

One example is the footpod employed by the Polar S625x

Polar S625x

The Polar S625x is a portable multisports computer in the form of a watch, made and sold by the Finnish company Polar Electro. Its primary features are running pacing information and heart rate data.More specifically, its features include:-Features:...

running computer.