To be able to run 5k fast you have to improve your endurance as well as your speed. If you just work on being able to run really quickly then you may run the first mile of your race really quickly but as your muscles won’t be prepared for running long distances you will fatigue a lot more than other runners who have conditioned themselves with long runs.
Is 10k too far for a child to run?
I’m 13 and many people would say that that is too young to be running these sorts of distances (most 10k races won’t allow anybody under the age of 16 to compete) however there is no evidence which suggests that kids are any more likely to get injured than adults or have any growth problems caused by running long distances. I think that it can only be a problem if the child is being pushed into it by their parents.
I didn’t try and run very fast in the early stages of the run because I wanted to work on building my aerobic capacity (around 70% of all respiration during a 5k is aerobic), however in the last mile I ran a lot faster (I got up to a 3:30/km pace towards the end) in order to simulate a “sprint finish” at the end of the race.
+ 1:29.9 (the last 0.35km)
With the “sprint finish”, I think that it is much better to begin building up your speed gradually from around 4km (in a 5k race) than to sprint the last 400m because you will probably be able to run a faster time doing it this way. You are also probably less likely to feel sick at the end of the race.