The purpose of speed endurance is to prolong the amount of time where a near maximal speed can be maintained.
Although the term is aimed at the long sprinters (200-400m), it also benefits the longer distances as well, in running events and other events like hockey.
The range for sprinters will usually be between 7 and 40 seconds where there is nearly complete recovery between each of the runs (especially if the runs are near 95% of maximum speed). A sample workout would be 2 x 300m or 325m with a full 15-20 minute recovery.
Running events up to 7 seconds utilizes the ATP/CP energy stores, and anything over 40 seconds is considered aerobic, or a mixture of anearobic & aerobic, depending of the intensity
Longer distance runners also benefits from Speed Endurance training. For example, an 800m runner would do intervals at a distance less than 800m (i.e. 400m repeats) at a speed of race pace or faster. Similarly, a marathon runner would do 1-mile or 1-kilometer repeats at race pace or faster speeds.
Keeping relaxed is key, as well as maintaining proper form throughout, especially the level of the hips being as high as possible. I like to imagine someone pulling and holding my hair up (like a bugs bunny cartoon) and enforcing the term “keep tall & relaxed”.
So, how can a guy who’s PB is 11.54 sec for the 100 meters run a world record in the 400m of 43.18?
In theory, it’s possible.
11.54 is about 10.54 if you take in account 1 sec for acceleration out of the blocks. This translates to an average speed of 9.48m/s, or about 42.18 sec for 400m. Add 1 sec for acceleration, and voila, you have 43.18!
So when a young lad shows up at the track with a PB of 11.3, I tell him, “Son, if you ran your 100m, kept going for 400m, and don’t slow down, you would break the world record!”
It’s not as simple as that, but it just shows you the importance of speed endurance. And a lot of other factors.