A new research examined different types of warm-up protocols and their effects on 800m running performance.
Key factor to improve 800m training is to use a protocol that contains sustained high-intensity exercise prior to the run.
One of the interesting side notes of this paper is a significantly higher vo2 peak in athletes who followed that protocol, perhaps due to increased blood lactate concentrations after the warm-up and prior to the 800 meter race.

Read the full paper here