Impairment of anaerobic capacity in adults with growth hormone deficiency

Abstract

Context: The anaerobic energy system underpins the initiation of all physical activities, including those of daily living. GH supplementation improves sprinting in recreational athletes, a performance measure dependent on the anaerobic energy system. The physiological and functional link between GH and the anaerobic energy system is unknown. Objective: The objective was to investigate whether anaerobic capacity is impaired in adults with GH deficiency (GHD) and to assess its functional significance. Design: This was a cross-sectional study. Participants: The participants were 13 adults with GHD and 13 age-, gender- and body mass indexmatched normal subjects. Main Outcome Measures: Anaerobic power (watts) was assessed by the 30-second Wingate test, and aerobic capacity was assessed by the VO2 max (L/min) test. The functional assessment comprised the stair-climb test, chair-stand test, and 7-day pedometry. Quality of life (QoL) was assessed by the QoL-AGHDA questionnaire. Lean body mass (LBM) was quantified by dual-energy x-ray absorptiometry. Results: Mean anaerobic power (5.8 ± 0.4 vs 7.1 ± 0.3 W · kg LBM-1; P < .05) and VO2 max were significantly lower in adults with GHD. The duration of the stair-climb test was longer (19.4 ± 0.7 vs 16.5 ± 0.7 s; P < .01) in adults with GHD and correlated negatively (R2 = 0.7; P < .0001) with mean anaerobic power. The mean number of chair-stand repetitions and daily step counts were lower, and the QoL-AGHDA score was higher in adults with GHD (P < .05). In a multiple regression analysis, age, gender, LBM, and GH status were significant predictors of mean anaerobic power. Mean anaerobic power significantly predicted stair-climb performance (P < .01) and QoL (P < .05). Conclusions: Anaerobic capacity is subnormal, and it independently predicts stair-climbing capacity and QoL in adults with GHD. We conclude that GH regulates anaerobic capacity, which determines QoL and selective aspects of physical function.