I can provide information regarding the dynamics of DD from a perspective that is generally recognized as the underlying cause. If the left ventricle walls of the heart are enlarged that almost always cause the walls to be rigid and unable to relax sufficiently to expand during the filling phase of the heart cycle. Also, the chamber size may be reduced as well. The result is less blood available to be pumped into circulation with each heartbeat.
An athlete's heart also increases the heart wall muscles as well, but that condition reverses when the exercise protocol is reduced. The difference with an athlete's hypercardiomyopathy from heart muscle disease is that the heart cells (myocytes) are lined up differently. The athelete's heart myocytes (cells) line up end to end and do not lose their ability to expand and contract, and muscle disease cells line up side by side.
The treatment for the enlarged heart walls can be medication the reduces the force of contractility and help increase the flexibility of the walls. If medication is not successful there is surgery that that can remove the excessive mass.
There can be heart muscle damage do to excessive drinking of alcohol, drugs, some medication, virus, bacteria, etc. I don't believe there is any reversal of thickened heart walls, but the condition can slowed or stopped with lifestyle change if that is the cause or any offending agent.
Wall dimensions are echo estimates, and your doctor did not seem concerned, so there may not be a heart issue. Your heavy workouts may be the cause. Is your heart rate at rest below 60 bpm? That would be a good indication of a strong healthy heart from your heavy workouts.
Thanks for sharing, and if you have any further questions or comments you are welcome to respond. take care.