Strenuous: adjective :vigorously active : energetic.
From ” Metamorphosis” by Franz Kafka, “what a strenuous career it is that I’ve chosen! Travelling day in and day out. Doing business like this takes much more effort than doing your own business at home.”
Now i understand that Gregor Samsas career requires him to be moving around alot. Also, it requires him to be exceptionally active.