Thanks for writing to us
There are normally two below knee indentations due to the anatomy of the muscles and the knee joint . I assume that you are referring to the recently noticed prominence of the same which could be due to the workouts and nothing serious.
However if you have noticed visible swelling or fullness which can be indented with fingers on applying pressure then it is more likely to be the beginning of a muscle overuse injury
.Still I consider it less likely because you mention that there is no pain or limitation of movement involved.
What happens when we start exercising a particular part of our body is that the muscles undergo considerable stress
and if the technique is improper or the warm up/ stretching exercises are skipped then the muscles can get overuse damage resulting in swelling , pain etc.
I do hope that you have found something helpful and I will be glad to answer any further query.