The other aspect to speed work is working with raised lactate levels in
the body. This is caused by running at a pace which doesn't allow the body
to use oxygen to release energy, which is fine, but it releases a waste product,
commonly known as lactic acid. If this build to a high level then it becomes
crippling to the body in terms of performance and you are forced to slow.
Long distance running is about controlling you pace so you are running
at just below the anaerobic threshold level (past which point lactic acid is produced), but
injections of pace, whether at the end of a race or a burst during it, mean
an athlete will need to go faster than this from time to time.
Training for this involves running faster than race pace, usually for
distances between 300 and 600m with recoveries that are often a bit longer than
you would have in other session - maybe 2-3 minutes.
A good session for this kind of training would be 8 x 400m with 2 minutes between each,
with the aim of running about 8-10 seconds a lap faster than your 10k pace.