I build muscle easily in my arms. Because of that, I cannot go heavy with weight training. I've been doing Horizontal Conditioning workouts for the past 6 months and my arms now are very defined and compact. I've never had results like this lifting weights even with high reps and light weights. All of our bodies are different so you need to do whats best for you. If you are unhappy with your arm development, i suggest cutting back on your frequency of arm training and/or amount of weight lifted.