Just to add to this comment, strength increased with cross-sectional muscle area. Neural adaptation is not entirely separate, but yes the stimuli for increasing each can be generally separated into the low or high rep schemes. For those doing any sort of strength training, as long as you progress in weight for the first 3-4 years gaining muscle mass is unavoidable and not a bad thing at all. Hypertrophy is a well studied area of sport science and as long as you maintain a healthy diet, building muscle is not a negative thing in the least. It even helps with longevity by counteracting the muscle loss associated with aging.