biceps are fast twitch fibers which respond very well to androgens. And arnolds delts and neck and etcetc blow away any natty. Tons of juicers with sht delts too no absolutes...
you cannot tell the makeup of ones muscle fibers without doin a muscle biospsy on that specific muscle group - muscle type I, IIa, IIax are all genetically predetermined - you cannot say biceps are fast twitch or the chest is - chest is made up of diff muscle groups as is, pectoralis minor pectoralis major, etc
the determining factor in the type of muscle fiber is genetics - why so are sprinter some are runners
type of fiber determines how energy is produced without the presence of oxygen -(no o2) anaerobic exercise - gettin deisel