A natural trainer can probably put on an additional 30-40 pounds of muscle. Muscle growth requires the proliferation and differentiation of satellite cells. When this stops, so does muscle growth. Muscles can also grow by increasing the number of cells (hyperplasia). This is greatly enhanced by using testosterone. It also happens in natural trainers depending on their age and training style. Bone structure and height play no role in muscle "growth". They only play a role in a muscle's appearance. There are other and more important factors involved - such as hormonal milieu, efficiency and levels of various enzymes pertaining to biochemistry (which also determines how your body handles nutrients), length of muscles and attachment of tendons etc etc. just to name a few. Nutrition (supplements) also plays a role. With HST the same muscularity can be reached in much less time. Under the right conditions, muscle mass can increase dramatically within a few weeks. Theoretically, with heavy drug use, a human could probably put on 20 pounds in 4 weeks. That same person could probably put on 50-60 pounds in 12 months. I have never personally seen anyone do this though. Reaching your potential while training natural is still going to take time...years. But you can knock off quite a bit of time with HST and good nutritional and supplementation practices. Please understand that when people ask me answer questions like, "how big can someone get", I have to be conservative to avoid undue criticism...I couldn't promise anyone 60 lbs of muscle...that’s quite a bit of extra muscle for a natural trainer. I don't really know how much I have "put on" because I began lifting at age 8. So, I don't know how big I would be without lifting. I did get down to 155 however after a severe illness. Since then I have gained about 60 pounds of LBM. To optimize HST a person should train twice per day. He/she should use 2 routines, and AM program and a PM program. Some exercises could be repeated but most should change from morning to evening. The normal progression of weight increments and reps to be followed. That is twice per day, 3 times per week. So still only train MWF but train twice on those days. I think I get a little more out of it when I do whole body twice. Although, I often split up upper and lower body when something cuts my workout short in the morning. Don't forget we're talking about volume too. The volume doesn't necessarily double. Just the frequency. There is the possibility that training once per day 6 days per week would be just as effective. But to be on the safe side, a rest day with massage is probably better to avoid injuries. On days off, you should receive a full body deep tissue sports massage. However, it isn't necessary to get to painful. The massage is simply a way to eliminate spasms, increase blood flow, increase protein uptake, and activate satellite cells. You shouldn't be "sore" after the massage. if it is done properly, your muscles will literally be pumped afterwards. A protein supplement should be taken before and after the massage. Calories should be high. Take bodyweight and multiply it by 18 or 20 depending on fat gain. This should give you about 500 to 1,000 above maintenance. Protein should be at least 0.8-1 gram per pound of bodyweight. Avoid saturated fat (within reason). Take a protein supplement before and after training. Use creatine as well. EFAs should be included (Fish oil and CLA). Also read the Eating for Size article. If you do these things you will grow very quickly. There are other things you can do but then you wouldn't be "natural" anymore. growth.