Hello, I am not a professional by any means, but I have been working out for a few years. I am 5'5" and also have "thick" arms. Just to give you an idea, I have been doing 6 - 7 hrs. of med. to hard cardio a week (that includes light weights and arm movement throughout) along with 6 sets (3 tri's / 3 bi's) of 16 - 25 reps with weight ranging between 10 + 55 lbs. for 3 months now and am just starting to see slimmer, more defined arms. Keep in mind it all depends on how your body distributes fat, etc. as to how long it will take. All I know is that my tri's are much larger than my bi's and I have seen definition sooner in them than my biceps. You have to really try too. You can't just throw the weight around; think about the muscle and follow through to the end. You need positive and negative force to grow. The cardio will help you to become defined and the weights will help to build more muscle. If the weight becomes too easy, add more, but if you feel joint or pain of any kind stop immediately. Hope I helped a little!