I am following a structured plan (just finished SSB LV 2), and I noticed that my RPE and HR are relatively lower indoors compared to outdoors for the same power output.
I use a favero assioma single-sided power meter pedal and calibrate it before every ride (indoors or outdoors). For a trainer, I have a tacx neo 1.
I notice that my heart rate outdoors for the same power output is a bit higher compared to inside. I recently did a 3 hour endurance ride and my heart rate was quite high for an endurance ride. I can say that I am getting fitter as my heart rate for the same power output is reducing when I am doing workouts on my trainer. I also recently did a sweetspot workout and I noticed my HR was relatively low throughout the workout, which is an indication that I am getting stronger. I checked the power graph of the 3-hour endurance ride and noticed that I was not keeping a very smooth pace. I live in a place with rolling terrain, so sometimes I am forced to ride the short climbs at tempo or above. The reason why my HR is lower when I am on the trainer is that my power graph is very smooth and ERG mode takes care of everything. When I ride outside, it is very spiky and erratic.
My question: how do I maintain a steady pace outside to last longer and avoid overcooking myself?