In my ongoing quest to learn about GH I ran across the following study:

http://www.ncbi.nlm.nih.gov/pubmed/20801067

Essentially the study took two groups (the third was a control group) and had them either perform a short term, high intensity workout or a longer, constant load workout. Afterwords, each group had their blood drawn at set time intervals to study their hGH, IGF-1, IGFBP-3 and cortisol serum levels. The find? They found that the short term, high-intensity workouts may in fact increase hGH and cortisol secretion but not IGF levels. Thought it was pretty interesting.