Fast, faster, fastest!

I joined my wife's running group this evening and chose to go with the fast element with the proviso that I might drop back. We set off at my '1km pace' so that didn't bode well for a 6km run! Anyway with a bit of effort I achieved some good times (including a sub-23 minute 5km) and suppose this is what's called a Tempo run. Whether skeletal muscle lactate is the barrier is debated in 'The Lore of Running' but it does make sense that it's not helpful to get stuck into a plodding pace rut.