Several recent posts have focused on intervals. Research has shown that a weekly speed workout will greatly improve your speed and endurance as well as help you become a more efficient runner. Basically, speedwork at its core is a period of intense running intermingled with slower recovery runs. Intervals are great and one of the best ways to increase speed and endurance, but they're not the only type of speedwork. Below are four types of speedwork sessions—Intervals or Repeats, Fartleks, Tempo Intervals, and Hillwork. The training plan you're using may call for just one of these types of speedwork or it may have you alternate between two or more. If you ever feel your speedwork is getting too routine and/or boring, then try swaping it out for a different type of speed workout to help refresh yourself mentally and physically.