Growth Hormone (GH) Enhances Anaerobic Capacity

Impact on Physical Function and Quality of Life in Adults With GH Deficiency

Viral Chikani; Ross C. Cuneo; Ingrid Hickman; Ken K.Y. Ho*,†

Disclosures

Clin Endocrinol. 2016;85(4):660-668. 

In This Article

Abstract and Introduction

Abstract

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 VO2max (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 dual-energy 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.

Introduction

Adult onset growth hormone deficiency (GHD) is characterized by abnormal body composition and impaired physical function.[1,2] Fat mass is increased, and lean body mass (LBM) is reduced causing diminished muscle strength and physical fitness.[3] Muscle function depends on muscle size, muscle fibre composition and the availability of energy. This energy is derived from mainly two sources, the aerobic (oxygen-dependent) and the anaerobic (oxygen-independent) energy systems.[4]

Anaerobic energy comprises preformed adenosine triphosphate (ATP) in the form of phosphocreatine and ATP generated from breakdown of glucose in the absence of oxygen (anaerobic glycolysis). In contrast, aerobic energy is derived from oxidative phosphorylation of metabolic fuels such as carbohydrates and lipids. The anaerobic energy system underpins both the initiation of all physical activity and intensive activities of brief duration such as running for a bus and sprinting.[5] Thus, impairment of anaerobic capacity may lead to an increased perception of fatigue during the execution of daily activities, a symptom commonly experienced by adults with GHD.[6]

There is evidence that GH plays a role in the regulation of the anaerobic energy system. In adults with GH deficiency, Sjogren et al.[7] found that short-term GH replacement repressed genes regulating aerobic metabolic pathways in skeletal muscle, favouring anaerobic energy production. In recreational athletes, Meinhardt et al.[8] reported that GH treatment for 8 weeks improved sprint capacity without affecting muscle strength suggesting facilitation by energy metabolism rather by muscle anabolism. This study, however, was undertaken in GH-sufficient subjects treated with a supraphysiological dose of GH. We recently reported that anaerobic capacity is reduced in adults with GHD compared to age-, gender- and body mass index (BMI)-matched control subjects.[9] As the GHD group comprised subjects with organic hypopituitarism, subnormal anaerobic capacity may have arisen from suboptimal replacement of other pituitary hormone therapies such as thyroid or adrenal hormone or concurrent chronic suboptimal health rather than GHD alone. The aims of study were to investigate whether (i) physiological replacement of GH improves anaerobic capacity in adults with GHD and (ii) changes in anaerobic capacity during GH replacement are associated with changes in measures of physical function and QoL.

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