Growth hormone (GH) enhances anaerobic capacity: impact on physical function and quality of life in adults with GH deficiency

Context Anaerobic capacity is impaired in adults with GH deficiency (GHD), adversely affecting physical function and quality of life (QoL). Objective To investigate whether GH replacement improves anaerobic capacity, physical function and QoL in adults with GHD. Design One-month double-blind placebo-controlled crossover study of GH (0.5 mg/day), followed by a 6-month open phase. Patients A total of 18 adults with GHD. Measurements Anaerobic power (watts) was assessed by the 30-s Wingate test, and aerobic capacity by the VO(2)max (l/min) test. Physical functional was assessed by the stair climb test, chair stand test, 7-day pedometry and QoL by the AGHDA questionnaire. Lean body mass (LBM) was quantified by dualenergy X-ray absorptiometry. Results GH replacement normalized IGF-1 levels during both study phases. During the 1-month placebo-controlled study, improvement in stair climb and chair stand performance was observed during GH and placebo treatment; however, there were no significant GH effects observed in any outcome measure compared to placebo. Six months of GH treatment significantly increased anaerobic power (P < 0.05), chair stand repetitions (P < 0.0001), daily step count (P < 0.05) and QoL scores (P < 0.001) compared to baseline measurements. GH treatment did not significantly improve VO2max. Improvement in anaerobic power independently predicted an improvement in energy and vitality domain of QoL (P = 0.03). Conclusions GH replacement improves anaerobic capacity, physical function and QoL in a time-dependent manner in adults with GHD. Improvement in the anaerobic but not aerobic energy system is likely to underlie the improvement in QoL in patients with GHD during GH replacement.