Dragon muscle growth in a fanfic might also be related to some special power source. Suppose there is a magical crystal in a hidden cave. When the dragon discovers and interacts with this crystal, it absorbs the energy from it, which then causes its muscles to grow exponentially. This growth not only changes its physical appearance but also gives it new abilities in combat and flight.
A dragon muscle growth fanfic could be about a dragon's journey of physical transformation. Maybe it starts with a young, small dragon and through various adventures, like facing tough battles or having to adapt to new environments, it begins to grow its muscles. For example, in a magical forest filled with strong magical beasts, the dragon has to constantly fight to survive, which makes its muscles develop over time.
Another aspect of a dragon muscle growth fanfic could be centered around a dragon's training. Just like a human athlete, the dragon might train under the guidance of an older, wiser dragon. They could practice flying at high speeds, lifting heavy objects, and doing other strength - building exercises. Over time, the dragon's muscles grow stronger and more defined, and it becomes a more powerful and respected creature in its dragon community.