In the lower repetitive area, mostly strength is built up and thus new strong muscle fibres are formed. It is particularly effective to train very heavy in a bulk. The faster you become stronger, the faster your muscles will grow. It must be paid particular attention to a good execution of the exercises in order not to hurt you. If your joints hurt, you should prefer to take a break for one week and train with light weight.⁣ In the range of 7-12 reps you are in hypertrophy training..... ~ Berceste