Background
Growth hormone is widely abused by athletes, frequently with androgenic steroids such as testosterone. However, effects on athletic performance are unclear.
Aim
To determine the effect of growth hormone alone, testosterone alone, or both combined, on body composition and measures of performance.
Methods
Participants: 96 recreationally trained athletes (63 men and 33 women) with a mean age of 27.9 years (SD, 5.7) recruited in Sydney.
Intervention: Men were randomly assigned to receive placebo, growth hormone (2 mg/d subcutaneously), testosterone (250 mg/wk intramuscularly), or combined treatments. Women were randomly assigned to receive either placebo or growth hormone (2 mg/d).
Measurements: Body composition variables (fat mass, lean body mass, extracellular water mass, and body cell mass) and physical performance variables (endurance [maximum oxygen consumption], strength [dead lift], power [jump height], and sprint capacity [Wingate value]).
Results
Body cell mass was correlated with all measures of performance at baseline. Growth hormone significantly reduced fat mass, increased lean body mass through an increase in extracellular water, and increased body cell mass in men when co-administered with testosterone.
Growth hormone significantly increased sprint capacity in men and women combined, by 0.71 kJ (95% CI, 0.1 to 1.3 kJ; relative increase, 3.9% [CI, 0.0% to 7.7%]).
When co-administered with testosterone in men, sprint capacity increased by 1.7 kJ (CI, 0.5 to 3.0 kJ; relative increase, 8.3% [CI, 3.0% to 13.6%]); other performance measures did not change significantly.
The increase in sprint capacity was not maintained 6 weeks after discontinuation of the drug. Side effects included swelling, joint and muscle pain and acne.
The authors speculate that the observed increase in the sprint capacity measure (Wingate value) might equate to a 0.4s increase over a 10s100m sprint but this is uncertain at this stage.
Limitations: Growth hormone dosage may have been lower than that used covertly by competitive athletes. The study was too small to draw conclusions about safety.
Conclusion
Growth hormone supplementation influenced body composition and increased sprint capacity when administered alone and in combination with testosterone. However other performance measures were not significantly changed.
