Although sports clothing is widely worn outside the gym these days, if you are going to actually be working out in it, you need to make sure that what you buy is fit for the purpose you have in mind.
Because it has become fashionable, there is actually a lot of so called sports clothing that is nothing of the sort - to be useful for working out it should use materials and design that actually help you in your workouts. Even if it doesn't actually make you go faster, it should be comfortable and unobtrusive when you exercise.
At its best, sports clothing works with the athlete to help them perform better - a good example was the form fitting rugby shirts that England wore when they won the rugby World Cup in 2003.
These tight fitting jerseys were specifically designed to wick moisture away from the skin, keeping the players cool in Australia's heat, while at the same time being difficult to grab, making the players harder to tackle.
They were thus a perfect combination of the right materials and the right design for the job.
When choosing what to wear for you own workouts, you need to look for materials that breathe and move the sweat away from your skin, and decide whether tight fitting or loose fits the bill better.