An inertial footpod is a device used to track running measurements such as speed, distance travelled, pace, etc., which would generally only be available on treadmills or with a GPS unit.
This device is usually small and attaches to a runner's foot. It uses one or more accelerometers and processes several times a second to compute speed.
One example is the foot pod employed by the Polar S625x running computer.
Stirling, Ross; Fyfe, Ken; Lachapelle, Gérard (2005). "Evaluation of a New Method of Heading Estimation for Pedestrian Dead Reckoning Using Shoe Mounted Sensors". Journal of Navigation. 58 (1): 31–45. Bibcode:2005JNav...58...31S. doi:10.1017/S0373463304003066. S2CID16086241.
Weyand, Peter G.; Kelly, Maureen; Blackadar, Thomas; Darley, Jesse C.; Oliver, Steven R.; Ohlenbusch, Norbert E.; Joffe, Sam W.; Hoyt, Reed W. (July 2001). "Ambulatory estimates of maximal aerobic power from foot-ground contact times and heart rates in running humans". Journal of Applied Physiology. 91 (1): 451–8. doi:10.1152/jappl.2001.91.1.451. PMID11408463.