Intensity is far, far more important than volume. The issue of volume, is a negative! As long as you tax all levels of strength you will allow for full muscular adaption. This can explain why powerlifters are very STRONG in the lifting portion of a movement but don't have the muscle size to match these amazing feats, because they're goal is to move weight through the concentric portion of the movement and don't tax the muscles ability to hold or lower a weight. I have put on 40 plus pounds of lean muscle naturally in the space of two and a half years training once every seven days and believe me and my training partner will never go back to the notion that more is better. The keys to growth in my eyes are proper form, intensity of effort and correct application of these two taken to failure using the minimum amount of repetitions to maintain a safe, injury free body, so obviously the less reps you do, the heavier the weight, the higher the risk of injury on the working muscles. I try to combat this by finding a happy medium and fail with slightly higher reps and lower weight but still extremely low reps. You can't expect to keep failing or working to just prior to failure or anywhere inbetween for that matter with the exact same weight and limited intensity forever and expect a muscle a need or even want to grow. YES there is an upper limit you will get to and that is because there is only so big and strong a muscle can become as determined by your individual potential, the cross-sectional size of a muscle across a joint, i.e.the length of tendons e.t.c.
