Scientists mine the rich seam of body wearable motion sensors

Body movement can be identified through clothing by passing a low voltage through a seam sewn from conductive yarn. Seam-based fitness trackers hold promise for tracking subtle movements (yoga, Pilates, rehabilitation, etc) -- something today's fitness watches struggle with. Stretching conductive seams reduces voltage, and the increase in resistance broadly indicates the level of stretch. Changes in voltage are recorded using a microcontroller.

source https://www.sciencedaily.com/releases/2021/06/210629120838.htm