Every run has a different purpose. The pace tells the body what that purpose
is, and the purpose runs the entire season.
Recovery pace
Easy runs between harder workouts, keeping the blood moving while the legs
rest.
Five minutes per kilometre and slower. Talk easily. The point is low stress and
high volume. Do not go faster because you feel good.
Long run pace
The long run teaches the body to burn fat and to run for hours. It is not
fast.
Only five to fifteen seconds faster than recovery pace. A long run and a
recovery run are the same pace on different days.
Threshold pace
The fastest pace you can hold as a conversation dies, usually around 4:15
per kilometre. The first workout where speed matters.
This is the pace of a 10k race, and training at threshold is how you move
that pace faster.
Interval pace
Short, hard repeats at the pace of a 5k race, recovered with easy jog, done
when the legs are fresh.
Three kilometres at 3:50, recovering with a kilometre at 6:00, repeated six
times. The body learns to tolerate lactic acid and the mind learns that it is
not fatal.
Race pace
The pace of the distance you are training for. Everything else is either
building to this or recovering from it.
For a marathon, about 4:30 per kilometre. For a 5k, 3:50. The week has one
workout at race pace, once the base is built.
The training week
One long run at long-run pace, one workout at threshold or interval pace, and
three or four days at recovery pace is the week that works for most of the
season.
Speed is specificity: the body does what you ask. Ask it to run fast in a
workout and it learns. Ask it to run fast in easy runs and it learns
that too, and then the workout is already hard before it starts.