If you are someone who has a tight budget and also prefer to go out to breathe fresh air and clear the mind while practicing open-air sports, Parc de la Ciutadella is the best choice for you; are many people that come to this park for the day or at night to practice running, you can see them on your own or organized groups who prefer to be led by a coach.
You can also see people enjoying a walk with your bike or rollers, not in the same park as the floor is dirt and rollers and skates are not suited to this type of terrain, but if, just opposite, where begins a long walk to the Arc of Triomphe; meeting place for skaters and skateboarders city. Besides the Official School of Skating it is very close to here and when weather permits come to this space to teach their open-air classes.
For smaller budgets, municipal sports center are usually the best and most affordable option if you want to practice a particular sport and prefer to take refuge from the weather, in both, winter and summer. In this link you can find information about these centers and its sports: Barcelona municipal sports centers
And if you're a born athlete, who practices a specific sport and want to know where to find the sports association or federation of the sport in the city, you must go to Institut Barcelona Esports which is the agency responsible for managing the sport in the city . It is located on the Avenida del Estadio, 30 and through its web find all the information for any sport in Barcelona. Institut Barcelona Esports
And finally, to find out all sporting events in the city, here you are the link. You should decide if you have trained enough to participate in any of them: Barcelona Sports Agenda
Get out of your student flat in Barcelona and get in shape!