Impact of Growth Hormone on Skeletal Muscle Strength, Power, Endurance & Agility in Prepubertal Boys With Short Stature

Abstract Context Growth Hormone (GH) enhances muscle strength and aerobic capacity in adults with GH deficiency, but GH effects in skeletal muscle are less well characterized in youth. Objectives To investigate the impact of GH on skeletal muscle in boys with significant short stature (SS) compared to age-matched, normally growing controls. Design Open-label comparator Setting Outpatient endocrine clinic Participants 45 prepubertal boys, SS, N = 30 (isolated GH deficiency or idiopathic SS) (mean(SE) age: 8.9 ± 0.3yrs; Height SDS:-2.3 ± 0.1); controls, N = 15 (8.8 ± 0.4yrs; HT SDS: -0.3 ± 0.2). Intervention Anthropometry, fat-free-mass, resting energy expenditure (REE) and muscle testing was performed at baseline, 6 and 12-months after daily GH (SS group) or observation (controls). Main Outcomes Skeletal muscle strength (isometric dynamometry (flexion/extension) upper and lower extremities) (principal), power (vertical jump), endurance (modified push-ups), and agility (timed shuttle-runs); fat-free-mass accrual, and REE (secondary). Results At baseline, the SS group had lower muscle strength in upper body (p≤0.027) and lower body (p≤0.007) vs. controls; similar lower body muscle power and agility; but lower endurance (p = 0.048). Baseline differences were significantly less after GH treatment, values in SS kids approaching those of controls by 12-months. Adjusting for height SDS and fat-free-mass between groups decreases detected differences in upper extremity muscle strength and endurance, but lower extremity muscle strength differences persist. No differences in REE were detected. Conclusions Boys with significant SS have quantifiable deficits in upper and lower body skeletal muscle strength, and lower physical endurance compared to normally statured controls. GH treatment for 12-months can improve these metrics in prepubertal boys with SS.