Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
strenuously [ˈstrɛnjuəslɪ] adv напряжённо
she strenuously denied the rumour она́ уси́ленно отрица́ла слу́хи
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.