Ok, so I'm usually not one to contradict the efforts of people trying to create things that will make the life of hijabis easier. In fact I really liked the idea of the Islamic swimsuits but when I saw the jilbab meant for doing sports in, I did chuckle to myself.
Have you ever tried running in a full length dress? The excessive material is so unpractical not to mention dangerous. I could hardly use a running machine let alone an exercise bike wearing one of these:
I know that the material is specially made for sports and I respect the fact that some women don't feel comfortable unless wearing the jilbab but practicality and safety in sports is important.
I think these sport suits I found on Primo Moda, an online hijab store, are a far more practical alternatives to the jibab while still maintaining an appropriate level of modesty:
If you do not like the idea of wearing these then you could join a ladies only gym which are avaliable in some places.
P.S. This is simply my opinion and I do not intend to offend anyone who wears the sports jilbab.