[CM213]

I think nbe can be affected by the gym and weight training to an extent. Even lean fit women usually have smaller breast, due to the lower body fat they carry (usually, I am stereotyping), women who have some low body fat also have few periods as well, which also plays a role in their development. So as a cis man taking herbal supplements to increase estrogen and trying to stop or lower testosterone without using surgical means or prescription medication, physical activity could stunt the affects of nbe and it's potential again to an extent.

I imagine being on HRT however is a different story. I'm sure the gym or physical activity could not stop the affects of feminizing and breast growth. But again it's all on our genetics as well. Everyone's mileage varies.