FIGURE 1.

The formulation of external vs internal variables for skeletal muscle hypertrophy. Although external variables (input) are indispensable to activate internal variables for skeletal muscle hypertrophy (output), the response of internal variables stimulated by external variables is the key determinant of skeletal muscle hypertrophy. The size of the color squares reflects the extent of the variables’ contribution to muscle hypertrophy. We are uncertain of the nature of the interaction between the variables and have shown them as multiplicative (•); however, we acknowledge that the function could be additive or more complex (i.e., an unknown function) relationship.