This is the 4851st most frequent Russian word.
интенсивно
Intensely.
The adverb 'интенсивно' describes the manner in which the studying activity was performed, indicating focused and concentrated effort.
Он интенсивно изучал новую тему.
He studied the new topic intensively.
Here 'интенсивно' modifies the verb 'проходили', emphasizing the dynamic or rigorous nature of how the lessons were carried out.
Уроки проходили очень интенсивно.
The lessons were conducted very intensively.
In this context, 'интенсивно' highlights the high level of effort and energy applied to the activity in the gym.