Let us open our minds further and examine what humans have adapted to while evolving over the millennia. Humans began as hunter-gatherers and there are still societies that function this way in the present day world. When examining this lifestyle, humans often had to walk for miles to find food, wait days for a successful hunt, and had to run to escape potential danger. The process of hunting for food had to involve miles of walking, intense bouts of running, jumping, pushing, pulling, and throwing. Then, there had to be days of repeated failed attempts for hunting game. Obviously, caloric consumption was not consistent from day to day. As a result, our bodies have evolved to handle various metabolic stresses.
Today, there still are those who have occupations which lead to an active lifestyle, but most have rather sedentary lives during the workday and must supplement their day with physical activity and the proper diet to maintain a healthy body weight. If we are not fortunate enough to have an occupation that keeps us extremely active, we need to supplement our day with an active session of exercise if we want to achieve a high leanbody mass. Why not mirror the hunter-gatherer lifestyle to achieve these goals? When looking closely at what they had to undertake on a daily basis, we can come up with the following.
Traveling long distance to find food = aerobic conditioning
Hunting expeditions which involved running, jumping, throwing, pushing, and pulling = anaerobic conditioning, strength training, and power training
Repeated failed hunting expeditions during a day = endurance training
I appreciate the application of biochemistry and human physiology to the maintenance of or creation of lean body mass, but a careful analysis of what gave rise to properly functioning human metabolism may take a simple and less confusing approach. We are hunter-gatherers by nature, so why not follow those necessary modes of exertion that have evolved and attempt to duplicate them in order to fulfill our lean body mass needs? To reach these goals it appears that our past suggests that we have evolved to handle strength training, high intensity interval training (endurance), and aerobic conditioning. Coincidentally, research has shown that a combination of these modes of training are ideal for creating an increased lean body mass. In addition, our ancestors did not have a consistent pattern of physical exertion and caloric intake. Therefore, our bodies are capable of adapting to changes in training for the better.
Even though there are many well researched methods for increasing muscle mass, reaching maximum oxygen intake, achieving unwanted fat loss, and elevating strength levels, being human and understanding how people have adapted to their surroundings provides a concrete foundation for understanding the methods of achieving a high leanbody mass.