Tendon and skeletal
muscle matrix gene expression and functional responses to immobilisation and
rehabilitation in young males: Effect of growth hormone administration

AP, Dideriksen K, Couppe C, Magnusson P, Schjerling P, Boeson M, Kjaer M, Langberg
H. J Physiol. 2013; 591(20).

Take Home Message: Human
growth hormone stimulates collagen expression in skeletal muscle and tendon and
abolishes the normal decline seen during inactivity and rehabilitation.

the loss of muscle and tendon during periods of immobilization and
rehabilitation is a challenge for medical personnel. The interaction of the
human growth hormone
(GH) and insulin growth factor 1(IGF-1; a protein involved in tissue
growth) helps regulate collagen tissue turnover within musculotendinous
junctions. Therefore, the authors investigated the effect of GH supplementation
on musculotendinous tissue during inactivity and rehabilitation. The authors
randomly selected one lower extremity to cast (from hip to ankle) for two weeks
among 20 healthy, physically untrained men (~23 years of age). The men then
completed a supervised unilateral rehabilitation program: 3 times a week for 6
weeks (18 sessions total). Participants performed unilateral (immobilized limb
only) knee extension and leg press. They increased sets and weight on a weekly
basis using a 5-repetition maximum test. Participants were randomly assigned to
receive subcutaneous injections of GH supplementation (10 participants; 33.3
ugkg-1day-1 to 50 ugkg-1day-1) or a
placebo (10 participants) for 8 weeks. Participants performed injections before
bedtime and the authors collected blood samples early the next morning to
measure hormone levels. The authors evaluated the immobilized limb at baseline
and then every two weeks for several outcomes: 1) Structural measurements (i.e.,
MRI of
medial quadriceps and patellar tendon cross-sectional area), 2) maximum
voluntary quadriceps contraction, 3) and patella tendon mechanical properties
(using strain gauge and ultrasound; tendon force/cross sectional area). The authors also
collected muscle biopsies from both limbs at baseline as well as 2 and 6 weeks
after rehabilitation. They used the muscle biopsies to measure the amount of
gene expression and collagen
fibrils. After the immobilization period both groups had decreased strength and
cross-sectional area, which was equally regained during their. Tendon fibril
diameter remained unchanged. There
was an initial decline in tendon stiffness (elasticity) after 2 weeks of
immobilization observed in the placebo group; however, it returned to baseline
level following rehabilitation. The GH supplementation group never encountered
a decline in tendon stiffness during immobilization, and following 6 weeks of
rehabilitation there was an increase in tendon stiffness. During
rehabilitation both groups had greater IGF-1 and collagen expression compared with
baseline; however, the rise was more pronounced in those that received the GH
injections. Additionally, IGF-1 gene expression increased during the
immobilization period only in the GH group.

researchers demonstrated that GH supplementation helps maintain levels of IGF-1
gene expression during inactivity and rehabilitation, which may abolish the
normal decline in tendon stiffness. It was interesting to note that there was
no change in muscle size, strength, or number of fibers, which suggests that
low levels of GH injections induce a collagen stabilizing effect during periods
of inactivity without effecting skeletal muscle contractile proteins. However,
baseline GH levels were not recorded so the gain could have been due to people
in that group having lower resting levels of GH and therefore they may have
benefited more from the supplement. This research suggests that young healthy
individuals may benefit from GH supplementation during periods of
immobilization and rehabilitation. Maintaining and increasing tendon stiffness
could accelerate full functional return to play quicker without the risk of

Questions for Discussion:
Would you give your athlete small doses of GH during periods of immobilization
and rehabilitation? Do you believe this would be safe in a different population
(e.g., females, adolescent)?

Written by: Jane McDevitt PhD
by: Stephen Thomas & Jeff Driban

Related Posts:

Boesen AP, Dideriksen K, Couppé C, Magnusson P, Schjerling P, Boesen M, Kjaer M, & Langberg H (2013). Tendon and skeletal muscle matrix gene expression and functional responses to immobilisation and rehabilitation in young males: Effect of growth hormone administration. The Journal of Physiology PMID: 24081158