The ATP schedule is, without a doubt, incredibly demanding and allows for little to no mistakes to be made.
Rafael Nadal, Novak Djokovic, Andy Murray and David Ferrer are among the top grinders in the game and are constantly running marathons and rapidly switching directions in lengthy, dramatic matches.
Roger Federer, similarly, plays a great deal of matches simply because he wins consistently, though he has never had a truly significant injury.
Nevertheless, some tournaments over the course of the calendar year ask for a lot from the competing players and in several cases the events take their toll on the top athletes.
Here are the most difficult, taxing tournaments in the world in order.