Cannot access Workout Exercises on Google Fitness API

Question

Using the tutorial (https://developers.google.com/fit/android/get-started), I was able to use the Fitness API to retrieve basic data such as steps. However, I have been unable to retrieve any DataSource related to DataType.TYPE_WORKOUT_EXERCISE.

Any ideas if workout exercises require any extra libraries or have any specific hardware requirements?

Here are my specs:

Handheld device: Nexus 5 on Android 5.1.1 using the latest Play Services 7.5.0
Wearable device: Moto 360 E939 on Android 5.0.2

edit

This is also the only documentation I can find regarding WorkoutExercises: https://developers.google.com/android/reference/com/google/android/gms/fitness/data/WorkoutExercises