You need to incorporate hard workouts into your training program if
you’re looking to extend the duration of your runs, and improve the
speed at which you compete. Hard runs are the key to your
adaptation as a faster, more efficient runner….they are the only
way you can achieve your goals on the road. As a runner you need to
experience physical stress with the understanding that when it
comes getting your miles in: The harder they come, the harder they
fall.