You can only build muscle tissue if you can generate stronger muscular contractions, so this calls on finding ways to increase exercise intensity. This should not be confused with exercise duration as maximum training intensity will actually shorten the time needed to achieve maximal muscular growth.
When you reach the point of muscular failure it is impossible to manage one more complete repetition of any exercise, at least not without losing form or correct technique. There is, however, one way in which you can increase the intensity even further and that is by completing one or more forced repetitions with the help of an experienced training partner.
The best way to achieve this is by keeping the same weights on the bar and have your training partner do no more than is necessary to allow you to complete up the three extra repetitions with good lifting form.
Beginning bodybuilders should avoid forced reps until they have learned good lifting techniques and have prepared their muscles for the stresses involved in this particular approach. Intermediate lifters should consider adding forced reps to one exercise in the pre-exhaust sequence. Advanced bodybuilders can utilize forced reps based on their own needs and judgement.