אסור, ואין להקל. וראה כאן: https://asktherav.com/is-it-okay-to-go-to-a-gym-that-is-mixed-if-the-crowd-there-are-dressed-like-regular-on-the-street/ https://asktherav.com/%F0%9F%9B%91-health-alert-%E2%9A%A0%EF%B8%8F-by-rabbi-yosef-braun/
האם מותר ללכת לחדר כושר מעורב? במקום שאין חדר כושר נפרד – האם אפשר להקל בזה?
אסור, ואין להקל. וראה כאן: https://asktherav.com/is-it-okay-to-go-to-a-gym-that-is-mixed-if-the-crowd-there-are-dressed-like-regular-on-the-street/ https://asktherav.com/%F0%9F%9B%91-health-alert-%E2%9A%A0%EF%B8%8F-by-rabbi-yosef-braun/
No. See: Halacha2go.com article #531: Mixed Swimming Exercise or Skating See also here: https://asktherav.com/there-is-an-exercise-class-with-only-female-participants-however-the-instructor-is-male-is-it-okay-to-join-the-class/ #3034
This may not be done. Reasoning: Certainly, if the instructor was Jewish there would be a problem of Lifnei Iver. This is true, even if the woman was…