There is no limit to exercising during the shari'ah that Allah has set, as long as it does not hurt itself in exercising, as long as it does not show aurat in exercise. Everything is done not because of the people, but because God told us such a thing.
Prophet sallallaahu 'alaihi wasallam said,
"A man can not see another man's nakedness and a woman should not see another woman's nakedness."
(HR Muslim No. 338)