Yes, relaxation is key.
whats the least stressful and most stressful form of speedwork.
in reference to younger athletes, I love to use flys. You have to first understand that they come in understanding things at varying levels.
I usually put a cone down at 20m for girls and 25 for boys. However depending on the “track age”, ability, and conditioning I have 15m and 25m options also.
For the sake of example though. Most girls can accelerate out to 20m but depending on top speed, acceleration, and speed endurance, etc, can usually only hold top speed for 20m. Once I see that they have become accustomed to holding the top end with better relaxation, I will move the second cone (at 40m) to 50m and have them work on holding (w/ form and relaxation) the top end to that point.
This workout varies based upon the pre-existing factors stated above. but if you tell the kids (and monitor closely) to only accelerate to the first cone and “hold” whatever speed they achieve thru accel. until they hit the second cone, they get better at not trying to accelerate more. That is usually how younger athletes get hurt.
I know this sounds vague but the rule I adhere to is that the CNS must be recovered in terms of days and minutes recovery between reps.
Two, the workout should scaffold and be appropriate to ability. Trying to have a kid go from a w.o. of 20m accel=>20m fly to a 40m fly without developing acceleration out to 25m simultaneously can throw the body off.
My favorite workout are “flys” just because you can concentrate on various elements of true speed with adequate recovery w/o thinking about not throwing up.