How often do you run, for how long and how far? Once you take a good look at your base mileage, you can work to increase the efficiency of these miles. Sprinting might be the quickest way to injury if your foundation isn't properly constructed. Let us know where you are at and we can go from there:8}

I agree with Toby that sprints could easily lead to injury if you do not have a good base. Injury prevention is key in this sport so when pushing hard during training, listen to your body. As far as speed goes.... running/adding in distance intervals 2 times a week would help. for example...run at  5K pace for 1 mile then slow it to an easy mile, go a little faster than 5k pace for mile three followed by another easy mile totaling 4 miles. or you can start out easy to warm up then finish all out!!  I love the challenge and push of this training run, try it out if it sounds like something you might be interested in & let us know how it goes.  Good luck

Happy running!