Growth hormone (GH) exhibits a great deal of molecular heterogeneity (there are over 100 isoforms in circulation) and we are only beginning to understand how exercise influences concentrations of GH isoforms. As the field of exercise endocrinology moves forward in the 21st century, greater recognition will be given to molecular heterogeneity that exists for many protein hormones within the paradigm of exercise and physical activity. Specifically, it is well established, but not well recognised, that GH exhibits a great deal of molecular heterogeneity, as over 100 molecular isoforms are thought to exist in the circulation. The importance of gaining a greater understanding of the exercise-mediated influences on GH molecular heterogeneity resides in the fact that the GH isoforms have diverse downstream metabolic and anabolic actions in target tissues.
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