Just a quick post to show the workout metrics available for customisation in WatchOS 4 using the standard Workout app. This may change when a series 3 watch is attached, but I'll update accordingly if it does.
UPDATE: Apple Watch series 3 has a barometric altimeter which means it can record elevation. So in the screenshots below we have three changes for Outdoor Walk, Outdoor Run and Outdoor Cycle - they each get the option for "Elevation Gain"
Click to expand