For most of us there is no real benefit from achieving a pump except for boosting your ego. Although, inability to achieve a pump is one symptom of overtraining . Fluid volume in the muscle and possibly blood volume decrease when glycogen stores are low. Intense cycling or swimming can also bring about a pump. The burning sensation during certain weight training exercises or high repetition training is caused by an accumulation of acid in the fatiguing muscle.
Anaerobic glycolysis utilizes carbohydrates and produces water and acid, or free hydrogen ions.
This acid does not clear sufficiently if blood flow is impeded. The vasculature within the muscle is temporarily occluded by the surrounding muscle when it is contracted intensely for a relatively prolonged duration. The excessive acid acts upon nerve receptors producing the localized burning sensation. Excessive acid accumulation also impedes muscular contraction. Acid interacts with calcium rendering it unavailable for muscular contraction.