Swimwear fabrics are generally polyester or nylon fabrics, opaque. Water will not stick to the skin, Permeability is not very good, not sweat absorption. Wearing a bathing suit while working out looks ok, but actually it's not scientific.
Fitness wear is generally knitted cotton fabrics, good air permeability, soft and comfortable, suitable for some basic sports, sweat absorption and other characteristics. Never go swimming in a gym suit. Gym clothes are usually tightly wrapped around the body at the touch of water, and have a little transparency, so that your body without a glance. If you don't mind being too sexy, you can wear a gym suit.