english 問題

Strenuous exercise

"Strenuous" is an adjective.

"Exercise" is an uncountable noun so don't put an "s" or any article (a/an).
This phrase is often used in Biology textbook. :)

Examples

What we did not know, he said, was the effect of strenuous exercise combined with the wrong kind of stress.
Regular light exercise is safer and more effective than occasional bouts of strenuous exercise.
You may feel ready to embark on more strenuous exercise; but do talk to your doctor before you get carried away if you have a history of heart trouble or high blood pressure, or any other health problems such as bronchitis or emphysema.

Yes, strenuous exercise is the technical term used in sports and biological science textbooks.

I think 'vigorous exercise' is the closest in meaning.

Intense exercise 或 intense sports