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.