According to Oxford Dictionaries, "strenuous" is an adjective that means requiring or using great exertion or physical effort. Strenuous is often used when describing activities that may be considered tiring or laborious, such as working out, riding a bike or working at a job that requires physical activity.
Any action that requires a certain level of movement or activity can be described as strenuous. This term derives from the Latin word "strenuus," which means brisk or vigorous. Additionally, a brisk walk in the park would be considered a strenuous activity. Some synonyms of strenuous are energetic, zealous, demanding, and grueling.