Tendon and skeletal muscle matrix gene expression and functional responses to immobilisation and rehabilitation in young males: effect of growth hormone administration.
Level 2 - randomized trial
Randomized controlled trial in humans
PubMed 24081158 · doi:10.1113/jphysiol.2013.261263
What was done
Young men aged 20–30 years (n = 20) were randomly assigned to daily recombinant human growth hormone (rhGH, 33–50 μg/kg/day) or placebo. All participants underwent 2 weeks of unilateral leg immobilisation followed by 6 weeks of resistance training rehabilitation. Quadriceps muscle and patellar tendon cross-sectional area (CSA), maximal voluntary contraction (MVC) strength, and tendon biomechanical stiffness were measured. Biopsies of muscle and tendon were analysed for mRNA expression of collagen (COL1A1/3A1), IGF-1 isoforms (IGF-1Ea/Ec), lysyl oxidase (LOX), matrix metalloproteinases (MMP-2 and MMP-9), decorin, and tenascin-C. Transmission electron microscopy was used to examine tendon fibril diameter distribution.
What was found
In skeletal muscle, CSA and MVC declined during immobilisation and recovered during rehabilitation to a similar extent in both groups. Muscle COL1A1/3A1 and IGF-1Ea/Ec expression increased during re-training in both groups, with a more pronounced increase in the GH group. In tendon, CSA was unchanged during immobilisation but increased by ~14% in both groups after 6 weeks of rehabilitation. Tendon stiffness declined after immobilisation in the placebo group only, and increased during rehabilitation only in the GH group. Tendon IGF-1Ea and COL1A1/3A1 mRNA increased during immobilisation in the GH group only, and LOX mRNA was higher in the GH group than in the placebo group. MMP-2 increased with immobilisation in both groups, while MMP-9, decorin, tenascin-C, and fibril diameter distributions showed no changes.
Why it matters
This study demonstrates that growth hormone protects tendon mechanical stiffness and upregulates connective tissue extracellular matrix gene expression during disuse and rehabilitation, but does not enhance muscle mass or strength recovery.
Limits
The study sample size is small (n = 20, approximately 10 per group) and limited to healthy young men, preventing generalisation to females, older populations, or clinical tendon injury cohorts. Exact effect sizes, variance, and safety outcomes for rhGH administration are not reported in the abstract.
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