I've been doing a lot of Rouvy riding for the last 2 years. Rouvy uses 7 zones so I've been doing mostly zone 3. As I review my rides, I find that my watts are increasing for the same heart rate. Most of my rides are 2 hours ( 3 to 4 times a week). I sometimes finish out the last 30 minutes in zone 5/6. No structured workouts. But I can definitely see myself getting stronger over time.