"Ontario gyms are changing the way they operate to accommodate post-lockdown fitness - The Globe and Mail" https://www.theglobeandmail.com/amp/canada/article-ontario-gyms-are-changing-the-way-they-operate-to-accommodate-post/

So gyms are re-opening here, and you don't have to wear a mask during exercise. But you do otherwise.

During exercise, your metabolism - and thus the amount of air you breathe - increases by a factor of approximately 10x.

But I'm sure that 10% of the time you're wearing a mask will totally help! 😂