Energy-only workout

Tap the activities field on top of the screen to show all available Activities. You can choose to save only your active energy burned:

Activities view

Add the start date, duration and active energy burned of your training and tap Record:

Energy-only workout

Your workout is saved in Workout Records and your iOS Health App in Health Data > Activity:

Workout in Health App

By default Workout Records will show your workouts for the past 7 days. To list previous records, tap show more:

Workout in Workout Records