Athletes must have a certain degree of flexibility in order to attain their speed potential. If an athlete is too stiff then they won’t be able to open their stride and will suffer from improper movement mechanics. This is one of the issues I see over and over again with young and old athletes. Most don’t take the time required to improve their dynamic flexibility (it’s not really that much time) and their mechanics suffer as a result.
In order to run at full speed the hip complex needs to be flexible. Most athletes don’t need to do a front or side split, but they should be quite flexible in the hips. Using both static stretching (post-workout) and dynamic stretching (pre-workout) athletes should focus on becoming flexible in the glutes, hamstrings, quads, and hips.
When running encourage your athletes to continue to raise their knees. They should be attempting (especially at first) to lift the knees higher and higher as they progress. This will both work on that flexibility and underscore the need for it.
This is often ignored by athletes but it is important to have a reasonably flexible shoulder complex. The upper body must remain relaxed while sprinting despite the powerful arm motions involved. If the shoulders and upper back are too tight then this relaxation cannot occur. Also, if the athlete is anything but a track runner, chances are they could stand to improve their shoulder, upper back, and lat flexibility
Is There Such a Thing as Too Flexible?
There are limits to how flexible an athlete needs to be, and that will vary depending on the sport. In order to achieve maximum velocity of limb movement (and thus run or move faster) there needs to be some sort of a stretch reflex where the tendons are loaded and then rebound. If the athlete’s ligaments and tendons have been stretched way beyond their normal length then some of this rebound is lost.
To be honest this happens extremely rarely. Off the top of my head some of the only times I’ve seen this are with martial artists. In many martial arts classes stretching and flexibility is highly emphasized, and at times to a fault. Some very flexible practitioners have found that as they continue to gain flexibility they lose “snap” on their kicks.
For most athletes flexibility is important. Work on the dynamic flexibility through warm-up drills before their training with some mild static stretching if necessary. After training, while they’re still warm, perform a more complete static stretch to really reduce that tightening reflex.