Although a very good 40 yard dash time may be instrumental in a high school football player securing a college offer, or may elevate a college player's draft stock, inevitably; it comes down to who plays well, and who makes plays on the field. Having said that, the higher the level of football, the higher the premium on speed, quickness, and explosiveness. This impacts all non-kickers to varying degrees, but in this blog the focus is on wide receivers, running backs, defensive backs, and return men. In other words, the players most likely to need to be able to open up their stride and run at top speed for a significant distance on a football field.
My contention is that football players, especially those at the positions I specified, shouldn't just settle for speed training that focuses on getting the 40 time that will satisfy the coaches. Since, ultimately, the players will be judged by performance on the field, the player's aim should be to train to develop their speed totally, and utilize it to improve themselves as players. My belief is that some training like a 100/200 meter track sprinter is what is required to totally develop sprinting speed..
Training like a track sprinter means not only training to start and accelerate explosively, but also to be able to, like a 100 meter sprinter; be able to accelerate up to about 40-50 meters, and then be able to hold that top speed for another 30 meters or so before trying to minimize deceleration. If you've watched football for awhile, you've seen quick guys that may have good moves or whatever, and are able to break into the open, but because they are more quick than fast, inevitably they are going to get run down by somebody.
Check out parts of this NFL Films 10 Fastest Players of All-Time video, and note how they have command of the entire field, and are able to use their speed to take it to the house from anywhere on the field. Not on the list, Eric Dickerson and Barry Sanders exemplified that type of speed also. A key point, however; is these were all highly skilled players that were able to use their great speed effectively. We've all seen super fast guys in football that couldn't play, and basketball players that could jump out of the gym but had little skill. For high schoolers looking to play at the college level, check out this What Recruiters are Looking for link, and note how many attributes other than speed are seen as important to college coaches.
Ideally, the athlete will be able to train for and compete in track in the off season, reaping the benefits of; the conditioning and the development of sprint fundamentals. Then during the spring and summer the focus can be on football preparation, which, includes the conditioning that is to support success on the field for all four quarters, but should also support the type of running the player intends to demonstrate during the season, ie; 80+ yard runs for running backs, receivers, and return men. If not running track in the off season, I believe some 100/200 meter training can be judiciously sprinkled in and still yield some benefits. I do oppose, however, replacing traditional football preparation during the pre-season and during the season with this type of training.
As for preparing to run the 40 yard dash, for a track sprinter, there are some adjustments, but if the sprinter is fundamentally sound, the transition should not be too difficult. The 3 point starting stance is one obvious aspect that the track sprinter will need to get accustomed to, and since the 40 is such a short distance, the sprinter's; drive phase, transition to maximum velocity, and maintenance of that velocity are affected. After each gets out to a good start, note how the winners of these 100 meter dashes stay in a driving posture for awhile, and how they gradually but not slowly, achieve their final upright running posture and relaxed running style, which allows them to continue running fast throughout the whole race. In contrast, note how these 40 yard dash guys more quickly become upright, and shortly afterward they are driving for the finish line. Football players, obviously, can also gain a lot of benefits from sprinting very short distances, ie; 1 yard, 5, yards, 10 yards, etc..., as being able to maximize quickness, explosiveness, and acceleration from a given stance, while executing the necessary techniques and skills for the position, is obviously critical.
If an athlete who's main sport is football, joins a track team to develop their speed, then this must be communicated to the track coach. The objective is for the athlete to experience the body positions and skills that go along with training for the 100 and 200 meter dashes, and the conditioning needed to run the 400 meter dash is also a good thing. These skills and conditioning is what translates better to the football field. If in regards to the sport of track and field, if the athlete's speed is more conducive to running distances greater than 400 meters, then my opinion is that sprinting still should be part of the training. The man we acknowledge as the greatest wide receiver in history, Jerry Rice, had good but not great speed, but note how effectively he uses his speed.
Once again, it goes without saying that first and foremost, football players need to be prepared for all of the demands of their position, but obviously, some of these demands have to do with speed in various ways, and like it or not, coaches, easily fall in love with speed.