Muscle Strength and Power, Maximum Oxygen Consumption, and Body Composition in Middle-Aged Short-stature Adults with Childhood-onset Growth Harmone Deficiency

Abstract

Growth hormone (GH) replacement in adult GH-deficient (GHD) patients is reported to have a long-term beneficial effect on muscle mass and function, these effects being greater in young males and in adult-onset compared with those with childhood-onset GHD. To date, more discordant data are reported on the degree of muscle impairment in untreated GHD patients, due to the large heterogeneity of this syndrome. Muscle maximum total isotonic strength (ST), lower limb maximum power output (W), maximum aerobic capacity (VO(2)max) and body composition (by tetrapolar bio-impedentiometry) were evaluated in seven short-stature adults with childhood-onset GHD and in seven age-matched normal-stature controls with comparable lifestyle and daily physical activity. Significant differences were found in body composition between control subjects and GHD patients, who presented higher adiposity (mean BMI+/-SD: GHD, 27.8+/-5.8 kg/m(2); controls, 22.1+/-0.8 kg/m(2); p=0.047), larger fat mass (GHD, 21.8+/-10.7 kg; controls, 8.8+/-3.5 kg; p=0.008), and lower fat-free mass (GHD, 65.8+/-11.4 %; controls, 87.0+/-6.5 %; p=0.002). In absolute terms, GHD patients attained significantly lower values in ST (GHD, 2479+/-493 N; controls, 4578+/-1476 N; p=0.008), W (GHD, 1092+/-452 W; controls, 1910+/-781 W; p=0.035) and VO(2)max (GHD, 1.68+/-0.40 l/min; controls, 2.67+/-0.84 l/min; p=0.035) than those attained by controls. The differences were still evident when the results were normalized by unit body mass, whereas they disappeared when the parameters were expressed per unit fat-free mass, suggesting for these patients the presence of an intrinsic muscle function in the same range as that of control subjects. Middle-aged and short-stature adults with childhood-onset GHD, who received discontinuous pit-GH substitution therapy only during childhood and have uncorrected long-lasting GHD, still retain a normal intrinsic muscle capability in attaining isotonic strength, generating anaerobic power as well as accomplishing oxidative processes. Nonetheless, it is not known which age-dependent evolution in motor dysfunction could be expected in this subgroup of GHD patients, when ageing processes add up to hormonal deficiencies.