One reason why you may not be getting faster is that you don’t know how to use your arms while you are sprinting. Yes, your arms! People look at us like we are crazy, but that is the first thing we teach when we are correcting an athlete's sprint mechanics. Fixing mechanical issues with the arms almost always fixes some problems that the athlete may be having in their lower body.
The perfect arm swing leads the legs by milliseconds during the sprint. That means that your legs will never be able to outrun a slow, inefficient arm swing. Also, almost all of the movement from the arm swing should come from the shoulder joint, not the elbow. Here is how to set up the perfect arm swing.
To start, your hands should be wide open with the fingers extended. Then, with your forearms parallel with the floor and elbows at approximately 90 degrees, keep your hands wide open, palms facing each other, and cock your wrist down so that your fingers point down 45 degrees. Then from there, swing your arm forward only trough the shoulder joint until your hand reaches chin height and your wrist is approximately 15 inches in front of your chin. This may be different for athletes with different limb lengths. The point here is your hand should be out and away from the body. Then, start swinging down, keeping your hand spread open, pass your pocket with your hand, and then continue to drive your elbow back behind the body until your hand is behind your butt by at least a good 12 inches with a bent elbow. If your hand is behind your butt by 12 inches but your elbow is straight, you have made a mistake. Keep your elbow bent. You should feel a good stretch in the front of your shoulder at this point. Then repeat the steps in reverse.
The last part of having perfect arm swing is it must be VIOLENT! Sprinting is the most explosive movement you can do and the arm swing needs to be the same way. If you aren't already used to having a violent arm swing, you may feel awkward at first, but trust me, you look awkward when you don’t use a violent arm swing.