Strength and its relationship to changes in fat-free mass, total body potassium, total body water and IGF-1 in adults with growth hormone deficiency: effect of treatment with growth hormone

Abstract

The present investigation examined changes in strength in growth hormone deficient (GHD) adults following treatment with recombinant human growth hormone (rhGH), and assessed their relationship to changes in fat-free mass (FFM), total body potassium (TBK), total body water (TBW), the concentration of TBK and TBW perkg FFM, and insulin like growth factor-1 (IGF-1). The investigation was double-blind and placebo-controlled for a period of 6 months; this was followed by a period of open treatment for a further 6 months. Patients were assigned randomly to experimental (E) and control (C) groups. In the first 6 months group E received rhGH and group C placebo; in the second 6 months both groups received rhGH. Serial data were analysed for 23 males (11 group E, 12 group C) and 20 females (10 group E, 10 group C). Body composition was assessed by dual energy X-ray absorptiometry, TBK and TBW. Muscle strength was recorded for arm flexion, leg extension and hand grip. Significant increases in FFM occured in the first 6 months in group E (2.3kg males, 1.4kg females) and in the second 6 months in group C (2.4kg males, 1.4kg females). There was a modest increase in absolute strength with time, although only three increments were significant (knee extension in group E males and arm flexion in groups E and C females), all of which occurred during the 6-12 month period. Allometric scaling did not improve the identification of significant increments of strength. The mean concentrations of TBK (males 57.0-58.6, females 51.4-53.9mmol) and TBW (males 0.65-0.69, females 0.65-0.68 l) perkg FFM, were significantly smaller at all stages of the trial than the reference values, suggesting that treatment had not fully normalized these variables. Likewise, the relationship between most of the increments of regional and total strength, and the corresponding increments of FFM, were generally poor and not significant. It was concluded that the reduced concentrations of TBK and TBW perkg FFM, which may be the effect of an inappropriate dose regime or mode of delivery, may, in part, contribute to the anomaly between increases in strength and FFM.