Posted by: PFB
One of the reasons volume training works is because you target a muscle, exposing it to an increasing number of repeated efforts (sets), the muscle adapts to this extraordinary stress by hypertrophying (enlarging) the targeted fibers.
As one trains for many sets with short rest periods, the fibers most often used will start to fail and the deeper, harder to reach fibers must then take over. Volume training reaches deeper into the muscle and works more muscle fibers causing them to enlarge is size.
This type of training enhances growth hormone production. More muscle size is also caused an increase in energy substances within the muscle (such as creatine and glycogen).
Also the high volume of sets gives you a huge pump, this increasing the number of capillaries within a muscle and the volume of muscle cell fluid (sarcoplasm) the muscle holds.
For more information go to Muscle Express The Fastest Way To Gain Muscle Mass