The moderate rep range has shown great results paired with the average lifting tempo due to the amount of time under tension for a working muscle group. (muscletech.com)
As reps are done, blood flow to the muscles under tension increases, bringing those areas oxygen and increasing heat. (gymjunkies.com)
The standard 8 - 12 reps usually aren't enough keep the traps under tension long enough, so move into the 12 - 15, or even 15 - 20, rep range. (bodybuilding.com)