If only the muscles and not the nerves going to the muscles are developed, the end result, in many cases, is a bodybuilder who appears stiff when he walks. Most barbell or dumbbell movements are fairly limited in movement and application. Nerves send electrical impulses to the muscles. Any experienced body-builder knows that cardiovascular exercise is a necessity in order to gain muscular size, improve circulation, and prevent injury. Most bodybuilders use treadmills in the gym for this purpose.
Treadmills are boring.
In some cases, you get shin splints. An open track isn't much better. Experiences I had had and things I had heard began to come back to me. Joe Louis had taken tap dancing. Walter Payton had taken ballet.