A key element in becoming a faster runner is to shorten the stance phase of gait without harming stride length. In other words, the idea is to produce the same propulsive force as usual during contact with the ground - but to make that contact shorter in duration (of course, an even-better scenario is to produce more force during contact with the ground, while making the contact more brief). Making ground contact more abridged automatically increases stride rate, one of the two factors which determines speed. Remember that running velocity = stride rate X stride length. Decreased ground contact time means higher stride rate, which means greater speed (as long as the shorter contact time doesn't reduce stride length).
It is the nervous system which regulates the length of the stance phase of gait, and thus it is the nervous system which must be taught to truncate the stance period while sustaining force production. One of the best lessons the nervous system can receive in order to shorten stance comes in the form of a drill called Shane's In-Place Accelerations (SIPAS). With SIPAS, stride rate can increase from the routine of 170-180 steps per minute to > 220 steps per minute, and thus the nervous system is learning to create a quicker reaction between the feet and ground.
SIPAS are straightforward to carry out. A runner should simply stand in running-ready position, with a slight forward lean of the body from the heels, the body linear, the shoulders back and down, the arms relaxed and held at the sides, the head relaxed and poised on the neck, and the ankles, knees, and hips just slightly flexed. Then, the athlete begins running in place, using a midfoot-strike pattern (please see photo above). For the first ~ 12 steps, the stepping rate is moderate, but the runner then begins to increase stepping rate rapidly until the maximal rate of stepping is reached. This max rate is sustained for a minimum of 30 seconds.
A very natural tendency is for runners to tighten up their upper bodies and look at their feet as they conduct SIPAS; this should be avoided. The upper body should stay relaxed at all times, and a runner should look straight ahead while carrying out this drill, as he/she would do during normal fast running.
For the first encounter with SIPAS, a runner can complete 3 X 30 seconds of continuous quick-stepping, with short, walking-around recoveries in between. This can progress to 7 X 30 seconds over time. A good tip for runners is that when they complete SIPAS they can think of playing a steady very quick drum solo on the ground with their feet, moving their "sticks" as quickly as possible. The use of a metronome can help some runners boost their stepping rate over 220 during this drill.
No added resistance of any kind should be utilized during this drill, as extra weight would slow things down. The idea, after all, is to enhance the ability of the nervous system to get the feet on and off the ground very quickly. SIPAS should be used during the fourth, explosive phase of training, along with the other nine exercises in this series. However, they can actually be utilized at any time of the year as a speed-enhancing drill. Although they are intense, and they will spike blood lactate, it is important to remember that the lactate (or lactic acid) will not cause burning, sorenenss, fatigue, or any other negative traditionally impugned to the chemical.