46 is not too low for a physically fit young person who is very active. Remember lance armstrong who won the tour de france bicycle rate five (or more) times in a row? He was in superb physical condition and his pulse rate was 35. The better your physical condition the slower your pulse rate. There is a formula for computing a target pulse rate. It varies with age and general physical condition. Here is a link for target pulse by age: http://www.revolutionhealth.com/articles/target-heart-rate/calc004 remember this is only for information..only a doctor can evaluate your heart rate and condition.