Impairment of anaerobic capacity in adults with growth hormone deficiency.

Abstract

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. The objective was to investigate whether anaerobic capacity is impaired in adults with GH deficiency (GHD) and to assess its functional significance. This was a cross-sectional study. The participants were 13 adults with GHD and 13 age-, gender- and body mass index-matched normal subjects. Anaerobic power (watts) was assessed by the 30-second Wingate test, and aerobic capacity was assessed by the VO2max (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. Mean anaerobic power (5.8 ± 0.4 vs 7.1 ± 0.3 W · kg LBM(-1); P < .05) and VO2max 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 (R(2) = 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). 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.