Do skeletal muscles compete with each other for growth?

Within the resistance training literature, a within-subject training model is often used to compare two separate training interventions within the same individual. While this model has some advantages related to statistical power, potential concerns have been raised when investigating changes in muscle strength. Conversely, it is currently believed that muscle growth is driven by local mechanisms. Thus, a within-subject design could potentially still be used if the sole outcome variable is changes in muscle size. What remains less clear, however, is whether the magnitude of skeletal muscle growth with resistance training is negatively influenced by the amount of muscle recruited within a given training period (e.g., upper body exercise only vs. same upper body exercise plus lower body resistance exercises). We hypothesize that there might be a competition for resources on skeletal muscle growth when more muscles are activated within a given training session and/or period, which might be moderated by energy availability. Determining the extent to which muscle exercised during resistance training influences skeletal muscle growth may provide important methodological considerations for researchers and practitioners alike. From a practical sense, if the competition of resources exists, one may benefit from specializing a certain muscle group to train within a given training period while deemphasizing other muscle groups.