At the moment VR fitness is found in the more active room-scale experiences. Beat games that have you swinging your arms around, adventure games where you’re swinging swords or shooting bows, and multiplayer games with twitch movements and dodging attacks.
To get the most out of VR fitness a user has to take the practice into their own hands, utilizing the fidelity of room-scale controls to engage in their own form of movements.
I use multiplayer VR games as a way to distract my mind from the monotony of a workout, spending the time between rounds of play engaged in body weight exercises. i.e. Squats, push-ups, pull ups, crunches, etc.
The engaging nature of VR games makes it rather easy to spend a sweat filled hour engaged in moderate intensity HIIT style workouts. (Though my Vive is located privately in my home)
I don’t see mobile VR tackling fitness until proper head tracking a la room-scale becomes standard on mobile headsets.