Tendon and skeletal muscle matrix gene expression and functional responses to immobilisation and rehabilitation in young males: Effect of growth hormone administration
Boeson 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.
Counteracting 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.
The 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 re-injury.
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
Reviewed by: Stephen Thomas & Jeff Driban