According to the Mayo Clinic Human Growth Hormone (HGH) can:
Decrease body fat
Increase exercise capacity
Increase bone density
Increase muscle mass
HGH levels are higher when we are young and growing and decrease with age. Raising HGH naturally is a good thing for most people. How to do that? One study, The time course of the human growth hormone response to a 6 s and a 30 s cycle ergometer sprint looked at the different responses to sprinting six seconds versus 30 seconds on a stationary bike. They found that:
Metabolic responses were greater after the 30 s sprint than after the 6 s sprint. The highest measured mean serum hGH concentrations after the 30 s sprint were more than 450% greater than after the 6 s sprint.