The pump is something that forces us to visit the gym again and again. Every athlete adores that feeling during and after intense weight training when the surplus of blood rapidly fills your muscles.
That cellular swelling, or more commonly “the pump” undoubtedly creates an unforgettable feeling providing a considerable, albeit temporary, increase in size of the muscle being trained, what in its turn gives a sense of accomplishment that strokes everyone's ego.
The actual data about this phenomenon shows that the pump is more than just a short-term increase in muscle size. According to several studies, the pump actually stimulates long-term adaptations within the muscle, promoting substantial gains in size and strength.
As Muscular Development reports, the muscle pump occurs when the veins that are taking blood away from the working muscles are occluded by the contracting muscle tissue, while the arteries that bring blood to the muscle remain unobstructed.
This creates a greater influx of blood into the area that causes blood to pool in the obstructed veins. This pooled, venous blood flows into capillaries connected to these veins, where it then leaks out of the thin-walled capillary and into the muscle cell, causing it to swell or “pump up.”
The capacity of this lifting style to induce venous occlusion was shown in a study by Tanimoto, where they demonstrated that low-intensity knee extensions with no resting phase induced venous occlusion— which decreased muscle oxygen levels more effectively than a second group performing higher-intensity knee extensions with a one-second rest period.
Furthermore, another study by Burd showed that a pump-inducing approach also increases muscle protein synthesis.
In general, very high-repetition sets combined with short rest periods produce quite a pump. Pushing the muscle like this will cause a tremendous demand for energy, driving lactic acid production and creating a fantastic blood flow to a muscle group trained.