Affecting it upwards, you mean. The goal of body builders wasn't exactly to become skinnier last time I checked.

Bodybuilders generally aim to build muscular mass through a cycle of high-intensity workouts under high-calorie conditions alternating with near-fasting (along with some even sketchier practices), but that doesn't say much about weight training in general; modern bodybuilding is incredibly specialized and has little to do with any kind of athletics.

By varying diet and the conditions of training, it's possible to use weights to increase endurance, build muscle mass, burn fat, or build strength, and while these all overlap to a certain degree they're not really all that strongly linked. An exclusive focus on one will tend to improve that one much faster than the others.