"vigorously maintained" is correct and usable in written English.
You can use it to describe something that is actively maintained with great effort. For example, "Robinson manages his garden with great care, vigorously maintaining the pristine condition of his plants."
Jones has vigorously maintained her innocence.
For more than three years, Mr. Milken vigorously maintained his innocence.
Was Ms. Zion's death due to cocaine, as the defense has vigorously maintained?
The 64-year-old Gupta, who remains free on appeal, has vigorously maintained his innocence.
Mr. Park and his co-counsel, Baruch Weiss, vigorously maintained their client's innocence and placed much blame on an inexperienced federal agent who they suggested was "seriously confused" and "gets it wrong a lot".
Even as critics argue that the threat of voter fraud is virtually nonexistent, Kobach has vigorously maintained that election criminals lurk around every polling booth, blaming state prosecutors for not pursuing the allegedly plentiful cases that his office refers to them.
Malek, his friends and supporters vigorously maintain, has atoned for his actions.
It is concluded that, despite the tendency on the part of the post-colonial leadership to vigorously maintain these policies, they were never designed with post-colonial development endeavours in mind.
Going forward, it is my strong belief that the United States has a solemn duty to vigorously maintain the classified nature of certain activities and information related to national security.
He continues to vigorously maintain that position sort of.
"Richie is shocked and bitterly disappointed to be facing charges, but vigorously maintains his innocence and intends to fight to clear his name, however financially straining that may be," Chalk said.
