Initially I thought that my growing muscle mass must have come from my increased attendance in water aerobics classes. However, I realized that I had increased class attendance 2-3 years ago, but only noticed the increase in muscle mass about 6-9 months ago. What was I doing differently? Well, I started taking Advanced Amino Formula daily (in the past I took it only sporadically). That was it. I'm an ectomorph (thin and no muscles) and never, ever had any arm muscles. However, after taking this product, I developed some really nice biceps. I showed them off to my Dr. who was pretty impressed, especially for a 69 year old woman! I rarely believe testimonials, but I'm writing as this product does build muscle. Believe me...or not. Just give it a try...and be consistent in taking the product daily.