This study shows long term GH administration increases muscle strength but muscular endurance is lower than controls. Keep in mind that both groups are sedentary people and that GH is also released in response to resistance training. So, supplementing with GH is similar to treating the group as resistance trained individuals in at least one respect. When we train low rep/high weight, we're attempting to induce fiber type switching from slow twitch (endurance) to bigger, fast twitch (anaerobic, explosive) muscle fibers. AAS aids in doing so as well. Based on the conclusion of this study, it seems GH may work by a similar action (at least one of its many actions).

J Clin Endocrinol Metab. 2003 May;88(5):2061-9. Related Articles, Links

Five years of growth hormone replacement therapy in adults: age- and gender-related changes in isometric and isokinetic muscle strength.

Svensson J, Stibrant Sunnerhagen K, Johannsson G.

Research Centre for Endocrinology and Metabolism, Sahlgrenska University Hospital, SE-413 45 Goteborg, Sweden.

GH replacement therapy in adults with adult-onset GH deficiency (GHD) has been shown to increase isometric and isokinetic muscle strength in a few trials with limited numbers of patients. In this single center, prospective, open-label study, the effects of 5-yr GH replacement therapy on muscle function were determined in 109 consecutive adults (61 men and 48 women) with adult-onset GHD. The mean initial GH dose was 0.88 mg/d. The dose was gradually lowered, and after 5 yr the mean dose was 0.46 mg/d. The mean IGF-I SD score increased from -1.54 at baseline to 1.53 at study end. A sustained increase in lean body mass and decrease in body fat was observed. The GH treatment induced persistent increases in isometric knee flexor strength, concentric knee flexor strength at an angular velocity of 60 degrees/sec, and right-hand peak grip strength. After correction for age and gender using observed/predicted value ratios, a sustained increase was also observed in isometric (60 degrees) and concentric (180 degrees/sec) knee extensor strength, average right-hand grip strength for 10 sec, and left-hand grip strength. At study end, knee flexor and extensor strength was 96-104% of predicted and hand grip strength was 84-90% of predicted values. The local muscle endurance was transiently decreased after correction for age and gender. No gender difference was found in the treatment responses in muscle strength. However, muscle strength (also after correction for age and gender) was lower in women than men throughout the study period. In conclusion, GH replacement therapy in adults with adult-onset GHD normalized isometric and isokinetic knee flexor and extensor strength. Hand grip strength increased but was not fully normalized.