High intensity weight training involves a very low volume of work approach to lifting weights but with a highly intense level of effort throughout the workout. Using high intensity correctly will result in muscular growth like you have never experienced. Bodybuilding and strength building have nothing to do with endurance, and training with a low intensity, high volume approach will do next to nothing to stress the body into making an adaptive response to it i.e. muscular growth.
If you question this because it’s not what you have been told, just look at who is more muscular: a sprinter or a marathon runner. With high intensity we hit the muscle in every way possible in the shortest time possible. By taking a set to positive muscular failure you are ensuring that the body is stressed enough to cause the desired adaptive response within the body. No amount of less intense sets will or can provoke the same response.
There are two ways to really stimulate muscular growth: overloading and time under tension. With high intensity you take care of both these factors. A set performed with the correct tempo takes care of the time under tension. You are also using maximum overload for a certain number of repetitions in every workout. There are three levels of strength: positives are the weakest, followed by static, then negatives are the strongest. During a properly performed set you will use all three levels of strength as much you can taking one set to positive failure. You can occasionally work the different levels individually but this has to be used very sparingly so you don’t tax your central nervous system too much. So remember: train hard, be the best you can be and always dare yourself to dream!