IMHO, it requires a balancing test, like a decision whether to go walking on the boardwalk in late spring, or to go to an amusement park in the summer. Although I think that under normal circumstances in my situation the answer would usually be not to do it, especially for a class.
It is probably a problem. Physical fitness classes often involve contact, and usually involve immodest clothes. It would probably be best to find a single-gender class (which is typically easier for women then men, since more non-Jewish women are also concerned with modesty than, relatively, non-Jewish men).
Perhaps there should be more of an effort for frum-sponsored single-gender health clubs.
If seminaries are to make women fat, and they go willingly, who is to say there is any market for a frum women’s gym? The person who is interested in both would have to be strange indeed. Also, why would a married woman need a gym? You are left with a very small target market.
There. Sem, weight, and shidduchim. I guess math jokes are just something I cannot do.
It is a shame the Kosher Gym is no more; I would feel very uncomfortable in a mixed setting while exercising, wearing shorts, etc. I also agree that mixed gyms are probably assur.
A Biologist, a Physicist and a Mathematician are sitting in a cafe. They see two people enter the condemned building across the street. A few minutes later, they see three people leave the building. The Biologist turns to his companions and explains, “They have reproduced.” The Physicist says, “The third must be an experimental error.” The Mathematician says, “If one more person enters that building, it will be empty again.”