Garmin introduced a standard (now open) that follow the entire pedal stroke and adds many parameters to that of a "normal" power meter.
Give "
Garmin Cycling Dynamics" a look.
Even the Garmin spec for pedal battery life change with the Cycling Dynamics (Ant+ high speed data) enabled.
If you'd like to get a look at a Fit file using Garmin Rally Pedals as captured using a Garmin Edge 830 contact me via PM.
EDIT: You're going to need 10 posts before you have access to the PM menus.
Barry