The Barbell Squat, just like any Squat works the lower body muscles which are vital to provide power into your step when running.
To set up for the Barbell Squat stand in front of the middle of your bar, facing away from it. From here grip the bar with your hands, it doesn't matter too much where they are as long as it is comfortable and each hand is an even distance from your body- you can use the markings on the bar to help this.
Take a few steps forwards so that the rack will not be in the way and begin your squat. You should go as deep as feels comfortable whilst keeping control of your back and not letting it bend. Push back up powerfully, squeezing your core and glutes at the top of the movement.
Throughout the movement ensure that your heels remain flat on the floor. If you do find them lifting off at the bottom of the movement add a few magazines or a plate to go under your heels so that they can remain firmly planted on the 'new' floor.