Impact of Growth Hormone on Skeletal Muscle Strength, Power, Endurance, and 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. Objective To investigate the impact of GH on skeletal muscle in boys with significant short stature (SS) compared with age-matched, normally growing controls. Methods This was an open-label comparator at an outpatient endocrine clinic. Participants were 45 prepubertal boys, SS, n = 30 (isolated GH deficiency or idiopathic SS) (mean [SE] age: 8.9 ± 0.3 years; height SDS: −2.3 ± 0.1); controls, n = 15 (8.8 ± 0.4 years; HT SDS: −0.3 ± 0.2). Anthropometry, fat-free mass, resting energy expenditure (REE) and muscle testing was performed at baseline, and 6 and 12 months after daily GH (SS group) or observation (controls). The main outcome measures were skeletal muscle strength (isometric dynamometry (flexion/extension) upper and lower extremities) (principal), power (vertical jump), endurance (modified pushups), 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 ≤ .027) and lower body (P ≤ .007) vs controls, similar lower body muscle power and agility, but lower endurance (P = .048). Baseline differences were significantly less after GH treatment, with values in children 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. Conclusion Boys with significant SS have quantifiable deficits in upper and lower body skeletal muscle strength, and lower physical endurance than normally statured controls. GH treatment for 12 months can improve these metrics in prepubertal boys with SS.