Colloquially, flash pump is becoming extremely pumped when not properly warmed up. It can take substantially longer to recover from than a normal pump.

By not warming up properly, the climber has failed to prepare their body for maximal work and the hormonal changes that take place when warming up have not occurred. Hence, capillaries have not dilated and blood flow to the muscles is limited. This means that the muscles end up working very hard with a limited energy supply, as well as finding it even harder to deal with the byproducts of maximal work. They fatigue quickly and this fatigue tends to be harder to recover from due to the inappropriate environment the muscles were asked to work hard in.