I am a 17 year old boy, about 5'11 and 135 pounds. I am actually very muscular, and my body has a nice shape to it. I took weight training at school this semester, and my body fat was a low 4.9% in February. Today, we were tested again and my body fat went down even more to 4.3%, which is way below the recommended 8% for my age. Even though I have gained lots of muscle, my gym teacher told me it is very low and it should be up more, but as long as I work out I see it dropping even lower. Is this healthy or should I be getting this checked out? Is there a healthy way to get it higher?