I only recently started using the Workout app. I don’t think OS 4 is really set up for my lifestyle. My definition of exercise is cabinet making in the workshop for an afternoon, light construction at the wildlife hospital where I volunteer, doing a 10 days worth of shopping in a big box store, etc… I fudge those into other categories. The only formal thing I do is outdoor walking.
Let me know if this changes in WatchOS 5.