There is a lot of controversy surrounding which kinds of exercise stimulate muscle growth and hypertrophy. With a large consensus reaching the conclusion that you will only get bigger if you use heavy-load training. Which usually involves less repetition and longer rest periods.
While this method does have a lot of analytical data surrounding it, the matter of the fact is that it is not the only avenue in which you can achieve muscle growth. The 'pump' is usually achieved when you exercise with lower weight at a higher rep count with fewer breaks in between. Eventually, you will start to feel the swelling in your muscles and the increased circulation which is a feeling, unlike any other. The 'pump' is perhaps most famously spoken of by Arnold Schwarzenegger during an interview in the 1977 documentary Pumping Iron:
The greatest feeling you can get in a gym, or the most satisfying feeling you can get in the gym is... The Pump... It's as satisfying to me as, uh, coming is, you know? As, ah, having sex with a woman and coming....You muscles get a really tight feeling, like your skin is going to explode any minute, and it's really tight - it's like somebody blowing air into it, into your muscle. It just blows up, and it feels really different. It feels fantastic.
Why is the pump important?
When you're feeling the 'pump', your muscles are essentially being filled with blood. Blood that is full of nutrients beneficial to those muscles that you are using. The process your muscles are going through while experiencing the pump actually involves them becoming larger because more blood is entering the muscles than leaving them. This allows for the muscles to have more opportunity to use the nutrients in the blood to further muscle development.
In addition to the nutrients that the blood is providing the 'pump' also as another interesting side effect. While the muscle itself is swelling, to some it may even feel like they're on the verge of exploding, this can actually be very beneficial to the development of more muscle mass. The body will believe it needs to generate more muscle tissue in order to fortify the 'walls' of the muscle as it becomes filled with blood, in turn creating more muscle tissue and more muscle mass.
The secret weapon: Drop Sets
As it turns out, using heavy-load training in conjunction with chasing that 'pump' might be the best way to achieve muscle hypertrophy in order to best facilitate muscle growth. According to a 2014 study published in Strength and Conditioning Journal, it was suggested that 'pump' training immediately following strength training with heavy-loads can optimize the potential for muscle hypertrophy. Meaning that drop sets, if done properly in conjunction with strength training can lead to more efficient muscle development.
The best way to do this, which is practised by a multitude of athletes is to perform your usual training of 5-10 rep max sets. Once you've finished the last set of your exercise, immediately drop the weight by about 30% and perform as many reps as you can until failure. You can repeat the process more times, but keep in mind that the more you train to failure the longer your muscle recovery can be.