Flexibility is often a big buzz word when it comes to training. Athletes want to be flexible and train in a way that allows that to happen.
How much flexibility does an athlete actually need though?
The short answer is whatever they need to get in the necessary positions for their sport. If they can get into all movements then they do not need to spend a lot of time trying to improve flexibility.
There is no recommendation for how much flexibility someone needs.
The difference is that we need to look at if flexibility is what an athlete needs. Flexibility is the range of motion of a given muscle. Joint range of motion is influenced by a lot of different factors, though. Most times, the length of the muscle is not an issue.
When looking at limited range of motion the big thing we have to consider is active vs. passive. If you lie on your back and raise one leg up straight, that is an active hamstring screen. Assume the same position but have a partner help you stretch and that is passive.
Not all active limitations are flexibility related. They are often strength related. The missing part of most range of motion training is mobility. Mobility requires that we actually move through good range of motion.
The key to mobility is movement. Sports are movement. If athletes cannot move then it needs to be addressed.
In the leg raise example above, an athlete that can passively get perpendicular to the ground has the range of motion. If they cannot do it actively, then no flexibility training is needed.
When sprinting the lead hip needs to flex, the trail hips has to extend, and the ankle has to dorsiflex towards the shin.
If an athlete cannot get into these positions we have to look and see why. If they can passively get there (most can) then they need to work on more control. Control can be developed through technique, strength, and stability.
Hip extension might be the perfect example. Fast athletes extend their trail hip, straightening the leg out and providing a push. This is influenced by glute strength, one of the underdeveloped muscles of the body, because most do not have issues getting their passively.
Improve glute strength while working on technique and then you will start to sprint faster. Exercises like deadlifts, hip thrusts, etc. become really important for building that strength in hip extension.
Injury risk is often a defense of training flexibility. Injuries are more likely to occur from a lack of strength. Weak muscles cannot absorb a lot of force and the demand of sport. Training for strength will be better for reducing this injury risk.
For that reason athletes should always be looking to improve their mobility. Mobility works hand in hand with strength, motor control, and stability. If all you do is stretch then you may need to take a look at your strategy.