[질문] i was exercising 틀린문장인가요exercise쓸때는 do를 가치써야한다는데

I was exercising는 괜찮은문장예요.do와 exercise를 같이쓰면,I did exercise.로 난(정말)운동해었다.로쓰면되죠.exercise에는명사도있지만,동사도있어서괜찮음