Training Load API for HealthKit?

Unless I’m being stupid - I cannot for the life of me find any documentation for implementing training load into my Apple Watch app. I’m thinking it’s not available. Basically I use the normal HealthKit APIs to start a workout on my Apple Watch using my app. It all works perfectly and after it saves the workout to the fitness app as if it was from Apple’s Workout app. Now the only thing missing is the ability to allow the user to edit and save their training load when their workout finishes (the little bars at the end of a workout where you can scroll from “Easy” to “All out”).

I guess Apple hasn’t make this API public - can anyone confirm or am I going crazy?