Many guys in the gym, do endless set of high rep, high volume exercises and assume the pump that they feel is inciting growth. They are wrong. Muscle growth comes from chronologically heavier weights on a weekly basis, in a 6-8 rep range, which will in turn cause tiny microtears in the muscle fascia fiber. When this fiber regrows it is stronger and denser than before, and thus is bigger in size. "Pump" is caused by blood rushing into the muscle fascia and temporarily stretching out the muscle. If your muscle gains have been slow, re-evaluate and prioritize your time spent in the gym. If you are just chasing a pump, you arent growing.